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Gas-phase tropospheric chemistry of biogenic volatile organic compounds: A review

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Abstract

Large quantities of non-methane organic compounds are emitted into the atmosphere from biogenic sources, mainly from vegetation. These organic compounds include isoprene, C10H16 monoterpenes, C15H24 sesquiterpenes, and a number of oxygenated compounds including methanol, hexene derivatives, 2-methyl-3-buten-2-ol, and 6-methyl-5-hepten-2-one. In the troposphere these organic compounds react with hydroxyl (OH) radicals, nitrate (NO3) radicals and ozone (O3), and play an important role in the chemistry of the lower troposphere. In this article the kinetics, products and mechanisms of the tropospheric reactions of biogenic organic compounds are presented and briefly discussed.

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... Once released into the atmosphere, air pollutants exert an influence on the chemistry of VOCs. Biogenic VOCs serve as a primary substrate for the formation of tropospheric O 3 and they can also react with O 3 , as well as OH and NO 3 radicals, which are commonly present in the atmosphere (Atkinson and Arey 2003). In pristine environments, with naturally occurring NO at very low concentrations (approximately 20 ppt) (Bianchi et al. 2019), the formation of tropospheric O 3 and NO 3 radicals is expected to be lower, which should limit the degradation of various VOCs. ...
... In pristine environments, with naturally occurring NO at very low concentrations (approximately 20 ppt) (Bianchi et al. 2019), the formation of tropospheric O 3 and NO 3 radicals is expected to be lower, which should limit the degradation of various VOCs. However, OH radicals can be formed under low O 3 by reactions that produce oxygen and its further reaction with water vapour (Atkinson and Arey 2003). It can be hypothesised that the degradation of airborne signals may be the main mechanism for the disruption of ecological interactions involving insects in the presence of air pollutants and the accumulation of oxidant radicals. ...
... The monocyclic monoterpene α-terpinene has been observed to have a lifetime as short as 1 min, while the sesquiterpenes α-humulene and β-caryophyllene have been found to have lifetimes as short as 2 min. In contrast, the reported lifetimes of oxygenated compounds are predominantly within the range of several hours to years (Atkinson and Arey 2003). Farré-Armengol et al. (2016) investigated the effects of elevated O 3 on the composition of a Brassica nigra floral volatile blend at various distances from a point source. ...
Article
Primary and secondary atmospheric pollutants, including carbon monoxide (CO), carbon dioxide (CO 2 ), nitrogen oxides (NO x ), ozone (O 3 ), sulphur dioxide (SO 2 ) and particulate matter (PM 2.5 /PM 10 ) with associated heavy metals (HMs) and micro‐ and nanoplastics (MPs/NPs), have the potential to influence and alter interspecific interactions involving insects that are responsible for providing essential ecosystem services (ESs). Given that insects rely on olfactory cues for vital processes such as locating mates, food sources and oviposition sites, volatile organic compounds (VOCs) are of paramount importance in interactions involving insects. While gaseous pollutants reduce the lifespan of individual compounds that act as olfactory cues, gaseous and particulate pollutants can alter their biosynthesis and emission and exert a direct effect on the olfactory system of insects. Consequently, air pollutants can affect ecosystem functioning and the services regulated by plant–insect interactions. This review examines the already identified and potential impacts of air pollutants on different aspects of VOC‐mediated plant–insect interactions underlying a range of insect ES. Furthermore, we investigate the potential susceptibility of insects to future environmental changes and the adaptive mechanisms they may employ to efficiently detect odours. The current body of knowledge on the effects of air pollutants on key interspecific interactions is biased towards and limited to a few pollinators, herbivores and parasitoids on model plants. There is a notable absence of research on decomposers and seed dispersers. With exception of O 3 and NO x , the effects of some widespread and emerging environmental pollutants, such as secondary organic aerosols (SOAs), SO 2 , HMs, PM and MPs/NPs, remain largely unexplored. It is recommended that the identified knowledge gaps be addressed in future research, with the aim of designing effective mitigation strategies for the adverse effects in question and developing robust conservation frameworks.
... Biogenic VOCs released from plants, including isoprene, monoterpenes, and sesquiterpenes, are important precursors of biogenic SOA (Atkinson & Arey, 2003;Kesselmeier & Staudt, 1999). Isoprene, one of the most abundant non-methane VOCs, originates primarily from terrestrial photosynthetic vegetation, including broadleaf plants and marine phytoplankton (Sharkey et al., 2008). ...
... Isoprene can preferentially react with OH radical (assuming OH ≈ 2 × 10 6 molecules cm 3 in air) to form SOA I owing to the short lifetime (∼1.4 hr at 25°C) of isoprene (Atkinson & Arey, 2003). The total concentrations of SOA I tracers were markedly higher in summer (45.4 ± 39.0 ng m 3 ) than in winter (2.3 ± 1.6 ng m 3 ) ( Table 2). ...
... Similar to the SOA I and SOA M-H tracers, the increase in β-caryophyllinic acid was correlated with the increase in O x during summer (Figure 4f). The lifetime of β-caryophyllene in the atmosphere is only several minutes (4 min, assuming O 3 = 7 × 10 11 molecules cm 3 ) owing to its high reactivity, and it rapidly reacts with O 3 to form βcaryophyllinic acid (Atkinson & Arey, 2003;. This further indicates that the enhancement of O x during summer can promote β-caryophyllinic acid formation. ...
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To investigate the combined impacts of anthropogenic and biogenic emissions on the formation of secondary organic aerosols (SOA), SOA molecular tracers, their corresponding volatile organic compound precursors, and other air pollutants were measured online during the winter and summer seasons of 2022 in an industrial city, Zibo, China. The results indicate that the average concentrations of SOA tracers were 16.1 ± 9.8 ng m⁻³ in winter and 99.4 ± 57.2 ng m⁻³ in summer. During winter, anthropogenic SOA (ASOA, the sum of SOA derived from naphthalene and mono‐aromatic volatile organic compounds) dominated, whereas isoprene SOA (SOAI) prevailed in summer. Correlation analysis between SO4²⁻ and both SOAI and high‐order monoterpene SOA tracers (SOAM‐H) (R = 0.46–0.72, p < 0.001) revealed that higher aerosol acidity facilitated the formation of SOAI and SOAM‐H, with SO2 emissions playing a significant role in leading to higher acidity. Most biogenic SOA (BSOA) tracers exhibited a significant positive correlation with NO3⁻, particularly in winter, implying the remarkable influence of NOx emissions on BSOA formation. The levels of BSOA tracers increased with NH3, indicating that NH3 can enhance the formation of BSOA. In summer, SOA formation correlated with Ox (Ox = O3 + NO2), indicating the substantial impact of atmospheric oxidizing capacity on SOA formation. During winter, aerosol liquid water content (ALWC) correlated well with SOAI tracers (i.e., 3‐hydroxyglutaric acid (3‐HGA) and 3‐hydroxy‐4,4‐dimethylglutaric acid (3‐HDMGA)), and 2,3‐dihydroxy‐4‐oxopentanoic acid (DHOPA) (R > 0.5, p < 0.001), indicating the important contribution of aqueous‐phase formation of SOA. These findings underscore the significant role of anthropogenic pollutant emissions in the formation of ASOA and BSOA in urban environments.
... NO x ) and give rise to a huge complexity of secondary components. The relative importance of the competing reactions (either by oxidation or photolysis) depends on the structure of the compounds as well as ambient conditions [42]. On the other hand, natural emissions of O 3 precursors can be affected by climate change. ...
... However, relatively little is known about BVOC emissions over southern Africa, except for savannah, Kalahari-and mopane woodlands [39]. VOCs are highly reactive species [11,42,82], and once entering the atmosphere are transformed by photolysis reactions (λ ≥ 290 nm) and oxidation by the OH radical during daytime, while at night transformations occur due to reactions with the NO 3 radical. Reactions with O 3 occurs in certain locations and times, whereas reactions with chloride (Cl) atoms can occur during daylight hours [42] in the marine environment [36]. ...
... VOCs are highly reactive species [11,42,82], and once entering the atmosphere are transformed by photolysis reactions (λ ≥ 290 nm) and oxidation by the OH radical during daytime, while at night transformations occur due to reactions with the NO 3 radical. Reactions with O 3 occurs in certain locations and times, whereas reactions with chloride (Cl) atoms can occur during daylight hours [42] in the marine environment [36]. Oxygenated VOCs and organic nitrates are to a large extent, similar to alkanes, alkenes and aromatics in their reactivity [81]. ...
Article
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Southern Africa is now a significant source of atmospheric pollution, having transformed from a rural to a developing region. The sub-continent is a source of atmospheric pollutants, including particulates, liquid and gaseous species produced from both natural and anthropogenic sources. Prominent hotspots for nitrogen oxide (NO x), particulate matter (PM) and biomass burning (BB) emissions can be seen on global maps and satellite retrievals. The seasonality of chemical transport mainly results from the seasonal swing of the Hadley circulation, the intertropical convergence zone (ITCZ) and subtropical westerlies along the transport pathways. The anticyclone induces strong subsidence motion, preventing vertical mixing of pollutants, hence capping high concentrations over land as they are transported across. This is manifested through temperature changes, cloud microphysical dynamics, atmospheric stability, the biosphere-atmosphere interactions as well as the oxidation processes. Once emitted chemical species show differences-either in the nearby or lower-and upper atmospheric levels in their dispersion, concentration, reaction rate, lifetime and/or oxidation capacity. Aerosols affect gas-phase chemistry via their light extinction potential and affect the photolysis rates of trace gases. Changes may occur through loss of gas-phase reactions, gas-to-particle partitioning or aerosol chemical modification. As part of efforts to understand chemical trace components and their atmospheric influence, this study highlights on the status of such species, their interactions and influence on air quality (AQ) composition over southern Africa. We propose an overview of gas-and particulate concentrations over several African localities, especially where daily WHO AQ threshold limits could be exceeded. The paper also aims to draw attention to African scientists and policy makers concerning pollution monitoring network in order to define national standards, to better control pollutant emissions and perhaps address impacts on AQ issues, pertaining to the growing African population and development.
... As BVOCs react with ozone, OH, and NO3 (in the case of nighttime chemistry), the subsequent reaction products often have lower 35 volatility that in suitable conditions can condense into new secondary organic aerosol (SOA) particles or contribute to the growth of existing aerosol particles (Bonn et al., 2009;Hallquist et al., 2009;Hodzic et al., 2016;Kulmala et al., 2004). BVOCs also affect the production and lifetime of tropospheric ozone through their photooxidation in the presence of NOx, as well as through their interactions with OH and other radicals (Atkinson and Arey, 2003). As reactive BVOCs compete with methane for reacting with ambient OH, they may also have an influence on the atmospheric lifetime of this greenhouse gas (e.g., Kaplan 40 et al., 2006). ...
... -10 s) chemical lifetime relative to MT, and that this is reflected in the observed concentrations measured by the Vocus, as a 425 substantial fraction is expected to react with atmospheric radicals or other compounds before reaching the measurement height (e.g., Atkinson and Arey, 2003;Rinne et al., 2012). This diurnal behavior highlights the interplay between constitutive (nonstress induced) emissions, driven by environmental conditions (principally, photosynthetic light and temperature), and the atmospheric stability within the forest canopy. ...
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Boreal forests emit terpenoid biogenic volatile organic compounds (BVOCs) that significantly impact atmospheric chemistry. Our understanding of the variation of BVOC species emitted from boreal ecosystems is based on relatively few datasets, especially at the ecosystem-level. We conducted measurements to obtain BVOC flux observations above the boreal forest at the ICOS (Integrated Carbon Observation System) station Norunda in central Sweden. The goal was to study concentrations and fluxes of terpenoids, including isoprene, speciated monoterpenes (MT), and sesquiterpenes (SQT), during a Scandinavian summer. High-frequency (10 Hz) measurements from a Vocus proton-transfer-reaction time-of-flight mass spectrometer (Vocus PTR-ToF-MS) were used to quantify a wide range of BVOC fluxes, including total MT, using the eddy-covariance (EC) method. Surface-layer-gradient (SLG) flux measurements were performed on selected daytime sampling periods, using thermal-desorption adsorbent tube sampling, to establish speciated MT fluxes. The impact of chemical degradation on measured terpenoid fluxes relative to surface exchange rates (F/E) was also investigated using stochastic Lagrangian transport modeling in forest-canopy. While the impact on isoprene was within EC-flux uncertainty (FISO/EISO<5 %), the effect on SQT and nighttime MT was significant, with average F/E-ratios for nighttime FMT/EMT=ca.0.9 (0.87–0.93), nighttime FSQT/ESQT=0.35 (0.31–0.41) and daytime FSQT/ESQT=0.41 (0.37–0.47). The main compounds contributing to MT flux were α-pinene and Δ3-carene. Summer shifts in speciated MT emissions for Δ3-carene were detected, indicating that closer attention to seasonality of individual MT species in BVOC emission and climate models is warranted.
... Monoterpenes, a family of C 10 H 16 compounds, comprise around 11% of global biogenic VOC emissions by mass 12 . They are considered as a crucial class of precursors for the global SOA budget 12,22,23 , primarily owing to their high reactivity (in particular, their tendency to undergo autoxidation) and the low volatility of the numerous oxidation products. α-Pinene is the most emitted monoterpene, accounting for approximately one third of the total emissions 24 . ...
Article
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Secondary organic aerosols (SOAs) significantly impact Earth’s climate and human health. Although the oxidation of volatile organic compounds (VOCs) has been recognized as the major contributor to the atmospheric SOA budget, the mechanisms by which this process produces SOA-forming highly oxygenated organic molecules (HOMs) remain unclear. A major challenge is navigating the complex chemical landscape of these transformations, which traditional hypothesis-driven methods fail to thoroughly investigate. Here, we explore the oxidation of α-pinene, a critical atmospheric biogenic VOC, using a novel reaction discovery approach based on molecular dynamics and state-of-the-art enhanced sampling techniques. Our approach successfully identifies all established reaction pathways of α-pinene ozonolysis, as well as discovers multiple novel species and pathways without relying on a priori chemical knowledge. In particular, we unveil a key branching point that leads to the rapid formation of alkoxy radicals, whose high and diverse reactivity help to explain hitherto unexplained oxidation pathways suggested by mass spectral peaks observed in α-pinene ozonolysis experiments. This branching point is likely prevalent across a variety of atmospheric VOCs and could be crucial in establishing the missing link to SOA-forming HOMs.
... BVOCs are highly reactive and short-lived, with lifetimes typically ranging from minutes to hours. Upon emission, they rapidly interact with tropospheric oxidant gases, thereby exerting a substantial influence on the oxidation capacity of the atmosphere (Lelieveld et al., 2008;Atkinson, 2000;Atkinson and Arey, 2003). ...
Article
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Biogenic volatile organic compounds (BVOCs) are emitted in large quantities from the terrestrial biosphere and play a significant role in atmospheric gaseous and aerosol compositions. Secondary organic aerosols (SOAs) resulting from BVOC oxidation affect the radiation budget both directly, through the scattering and absorption of sunlight, and indirectly, by modifying cloud properties. Human activities have extensively altered natural vegetation cover, primarily by converting forests into agricultural land. In this work, a global atmospheric chemistry–climate model, coupled with a dynamic global vegetation model, was employed to study the impacts of perturbing the biosphere through human-induced land use change, thereby exploring changes in BVOC emissions and the atmospheric aerosol burden. A land use scheme was implemented to constrain tree plant functional type (PFT) cover based on land transformation fraction maps from the year 2015. Two scenarios were evaluated: (1) one comparing present-day land cover, which includes areas deforested for crops and grazing land, with potential natural vegetation (PNV) cover simulated by the model, and (2) an extreme reforestation scenario in which present-day grazing land is restored to natural vegetation levels. We find that, compared to the PNV scenario, present-day deforestation results in a 26 % reduction in BVOC emissions, which decreases the global biogenic SOA (bSOA) burden by 0.16 Tg (a decrease of 29 %), while the total organic aerosol (OA) burden decreases by 0.17 Tg (a reduction of 9 %). On the other hand, the extreme reforestation scenario, compared to present-day land cover, suggests an increase in BVOC emissions of 22 %, which increases the bSOA burden by 0.11 Tg and the total OA burden by 0.12 Tg – increases of 26 % and 6 %, respectively. For the present-day deforestation scenario, we estimate a positive total radiative effect (aerosol + cloud) of 60.4 mW m⁻² (warming) relative to the natural vegetation scenario, while for the extreme reforestation scenario, we report a negative (cooling) effect of 38.2 mW m⁻² relative to current vegetation cover.
... All model simulations treat MT as a single isomer, which by default we implement based on α-pinene since it had the median O 3 reactivity (τ 30 ppb O 3 = 4.6 hr; Atkinson & Arey, 2003) across all MT isomers detected during FluCS Vermeuel, Millet, et al., 2023) and PEcoRINO (Vermeuel, Novak, et al., 2023). Sensitivity simulations were also performed instead treating all MT as β-ocimene (the most reactive isomer identified in the field studies; τ 30 ppb O 3 = 44 min); we will show in Section 3.5 that this had negligible effect on the computed in-canopy O 3 loss. ...
Article
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Dry deposition is the second largest tropospheric ozone (O3) sink and occurs through stomatal and nonstomatal pathways. Current O3 uptake predictions are limited by the simplistic big‐leaf schemes commonly used in chemical transport models (CTMs) to parameterize deposition. Such schemes fail to reproduce observed O3 fluxes over terrestrial ecosystems, highlighting the need for more realistic treatment of surface‐atmosphere exchange in CTMs. We address this need by linking a resolved canopy model (1D Multi‐Layer Canopy CHemistry and Exchange Model, MLC‐CHEM) to the GEOS‐Chem CTM and use this new framework to simulate O3 fluxes over three north temperate forests. We compare results with in situ measurements from four field studies and with standalone, observationally constrained MLC‐CHEM runs to test current knowledge of O3 deposition and its drivers. We show that GEOS‐Chem overpredicts observed O3 fluxes across all four studies by up to 2×, whereas the resolved‐canopy models capture observed diel profiles of O3 deposition and in‐canopy concentrations to within 10%. Relative humidity and solar irradiance are strong O3 flux drivers over these forests, and uncertainties in those fields provide the largest remaining source of model deposition biases. Flux partitioning analysis shows that: (a) nonstomatal loss accounts for 60% of O3 deposition on average; (b) in‐canopy chemistry makes only a small contribution to total O3 fluxes; and (c) the CTM big‐leaf treatment overestimates O3‐driven stomatal loss and plant phytotoxicity in these temperate forests by up to 7×. Results motivate the application of fully online vertically explicit canopy schemes in CTMs for improved O3 predictions.
... Pollinating insect species often rely on floral scent plumes, composed of VOCs, as crucial cues to locate flowers. However, the effectiveness of these scent plumes can be compromised or obscured by oxidizing air pollutants (Atkinson and Arey, 2003;Saunier et al., 2023). These pollutants can exhibit a dual impact, reacting directly with floral VOCs in the atmosphere and concurrently altering the biosynthetic pathways of Fig. 2. The effects of air pollution and flower availability on insect taxonomic richness and diversity. ...
... Criegee intermediates (carbonyl oxides) are formed by the ozonolysis of olefins in the atmosphere (Criegee and Wenner 1949;Calvert et al. 2000;Taatjes et al. 2012). Atmospheric trace gases like SO 2 , H 2 O, (H 2 O) 2 , NO 2 , carbonyl compounds and carboxylic acids are reported to react with the stabilised Criegee intermediates (SCIs) (Stone et al. 2014;Welz et al. 2014) Carbonyl compounds are released into the atmosphere mainly from anthropogenic and biogenic sources and get isomerised or degraded into other oxygenated hydrocarbons by atmospheric oxidants like OH, Cl and Criegee intermediates (Atkinson and Arey 2003;Mellouki et al. 2015). The reactions of the CH 2 OO with volatile carbonyl compounds are considered to be important as they can lead to less volatile acids and esters, which in turn participate in the formation of secondary organic aerosols (SOA). ...
Article
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Temperature-dependent kinetics of Criegee intermediate (CH2OO) with 2-pentanone were performed at 258–318 K and 50 Torr using pulsed laser photolysis-cavity ring-down spectroscopy (PLP-CRDS) technique. The measured room temperature rate coefficient was (3.84 ± 0.24) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹. The reaction follows a negative temperature dependency, and the corresponding Arrhenius equation is k4 = (1.76 ± 0.36) × 10⁻¹⁵exp{(3.18 ± 0.11) kcal mol⁻¹/RT}. The high-P limit rate coefficients obtained using CVT/SCT at CCSD(T)/aug-cc-pVTZ//B3LYP/6–311 + G(2df,2p) level of theory deviate from the experimental results, especially in the low-temperature region. At 258 K, the computed high-P limit rate coefficient exceeded the experimental value by more than a factor of four. Comparing all the reaction pathways, HCOOH was the major product formed in the title reaction. The atmospheric lifetime of 2-pentanone due to its reaction with CH2OO was calculated to be ~ 3000 days, rendering the reaction insignificant for inclusion in models of atmospheric 2-pentanone.
... Once BVOCs are readily oxidized in the atmosphere through reactions with tropospheric oxidants, primarily hydroxyl radicals (OH . ), they participate in recycling the nitric oxide (NO) into nitrogen dioxide (NO 2 ), which is then photolyzed into NO and oxygen singlet (O) to form ozone (O 3 ) with di-oxygen, as reviewed by Atkinson and Arey (2003). Oxidized VOCs are also a source of secondary organic aerosols (SOA) (Atkinson, 2000;Yu, 2000). ...
... [19][20][21][22][23][24][25] During daytime conditions, NMVOC oxidation is dominated by reaction with OH radicals and O 3 , while during the night, the dominant oxidant is the NO 3 radical. 6,23,[26][27][28] Due to the high variety of NMVOCs emitted and their individual degradation pathways driven by environmental conditions, a huge diversity of SOA precursors exists. Recent studies revealed a high impact of SOA formation through NMVOC oxidation from the NO x concentration. ...
Article
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Oxidation of emitted anthropogenic and biogenic volatile organic compounds (VOCs) and subsequent chemical reactions reduce the volatility of the products formed leading to secondary organic aerosol (SOA) formation. Despite the huge diversity of individual SOA compounds, SOA modelling is often simplified and estimated at the initial oxidation step neglecting chemical and physical process influencing SOA formation e.g. advection, deposition, chemical degradation and aging processes. To overcome this shortcoming, the chemical gas-phase mechanism URMELL was developed. URMELL treats more than 40 distinct oxidised gas-phase SOA (gasSOA) precursors with individual molecular characteristics and physico-chemical partitioning properties enabling a much more explicit gasSOA treatment for products of aromatics and isoprene oxidation. In this study, CTM simulations using COSMO-MUSCAT were performed with URMELL and compared with a simplified gasSOA scheme applying the widely used gas-phase mechanism RACM. The comparison indicates a delayed and thereby locally shifted gasSOA formation when applying URMELL. This effect is caused by the formation of multigenerational and multifunctional products along the transport trajectory whereby accounting for changes in the oxidant regime and leading to a multitude of gasSOA substances with URMELL. For isoprene and aromatics, URMELL simulates higher contributions of products with lower volatilities whereby aromatics generate even non-volatile products which can partition in new particle formation. The non-volatile aromatic products increase the average aromatic surface gasSOA concentration (30% on 20th of May 2014) and show unexpectedly high concentrations in remote spruce forest areas, away from the emission sources, highlighting the potential of the detailed schemes and its need for application in CTMs.
... Common HIPVs, particularly terpenoids and GLVs, are highly reactive with tropospheric oxidants, including O 3 , OH and NO 3 radicals. Consequently, several compounds have short atmospheric lifetimes, which range from several minutes to a few hours [37]. Studies on the impacts of elevated O 3 levels on floral scents indicate that the width of the odour plume and the distance it can travel downwind are both shortened dramatically as the level of O 3 pollution increases [38]. ...
... Organic pollutants are categorized based on their volatility, with the most volatile being the most hazardous [16]. VOCs contribute to atmospheric chemistry on regional and global scales, acting as precursors to secondary pollutants like ground-level ozone, peroxyacetyl nitrate (PAN), and secondary organic aerosols [17][18][19][20][21]. Low-volatility products from VOC oxidation contribute to secondary organic aerosols (SOAs) [22]. ...
Article
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Rajasthan, experiencing rapid industrialization and urbanization, faces critical air quality challenges, particularly concerning toxic volatile organic compounds (VOCs) such as BTEX (Benzene, Toluene, Ethylbenzene, Xylene). This study presents a long-term analysis of BTEX concentrations across various cities in Rajasthan, India, using data from the Central Pollution Control Board (CPCB) from 2017 to 2022. The findings revealed that the average ∑BTEX concentrations increased from 4.15 µg/m³ in 2017 to 12.29 µg/m³ in 2022, with a temporary decline in 2020. The Hazard Quotient (HQ) values for BTEX exposure ranged from 0.052 to 0.15 for males, 0.056 to 0.17 for females, and 0.09 to 0.29 for children over the study period, indicating higher health risks for children. Similarly, the Lifetime Cancer Risk (LCR) values varied from 6.04 × 10⁻⁶ to 1.92 × 10⁻⁵ for males, 1.09 × 10⁻⁶ to 2.24 × 10⁻⁵ for females, and 1.17 × 10⁻⁵ to 3.73 × 10⁻⁵ for children. The results demonstrate that children are at a greater cancer risk from BTEX exposure compared to adults. This study emphasizes the urgent need for effective air pollution control measures and continuous monitoring to protect public health, particularly vulnerable populations like children.
... 1−7 Increasing levels of phenolic compounds in air are a potential environmental concern due to their participation in tropospheric ozone production and secondary organic aerosol (SOA) formation. 8,9 Recently, the atmospheric fate of phenolic compounds has attracted significant attention from a chemical perspective. Phenolic compounds present on the surface of SOA can undergo direct photolysis, and oxidation reactions with hydroxyl radicals (HO • ), nitrate radicals (NO 3 • ), and ozone (O 3 ), which lead to their transformation during atmospheric transport and ulterior removal. ...
Article
Semiconductor photocatalysis with commercial TiO2 (Degussa P25) has shown significant potential in water treatment of organic pollutants. However, the photoinduced reactions of adsorbed catechol, a phenolic air pollutant from biomass burning and combustion emissions, at the air−solid interface of TiO2 remain unexplored. Herein we examine the photocatalytic decay of catechol in the presence of water vapor, which acts as an electron acceptor. Experiments under variable cutoff wavelengths of irradiation (λ cutoff ≥ 320, 400, and 515 nm) distinguish the mechanistic contribution of a ligand-to-metal charge-transfer (LMCT) complex of surface chemisorbed catechol on TiO 2. The LMCT complex injects electrons into the conduction band of TiO2 from the highest occupied molecular orbital of catechol by visible light (≥2.11 eV) excitation. The deconvolution of diffuse reflectance UV−visible spectral bands from LMCT complexes of TiO2 with catechol, o-semiquinone radical, and quinone and the quantification of the evolving gaseous products follow a consecutive kinetic model. CO2(g) and CO(g) final oxidation products are monitored by gas chromatography and Fourier-transform infrared spectroscopy. The apparent quantum efficiency at variable λ cutoff are determined for reactant loss (Φ −TiO2/catechol = 0.79 ± 0.19) and product growth ΦCO2 = 0.76 ± 0.08). Spectroscopic and electrochemical measurements reveal the energy band diagram for the LMCT of TiO2/catechol. Two photocatalytic mechanisms are analyzed based on chemical transformations and environmental relevance.
... Stem terpene profiles ) as well as their temperature responses (Sallas et al. 2003) differ from needles, but temperature-induced changes in stem terpene concentrations were not included in this study. Terpenoids in general are very reactive with atmospheric oxidants (Atkinson and Arey 2003), and these reactions can lead to formation of secondary organic aerosols (SOA). Climate feedbacks of SOA are uncertain, but some models indicate that increased diffuse fraction of solar radiation by SOA can improve light-use efficiency of plants and increase photosynthesis and growth (Rap et al. 2018), and SOA action as cloud condensation nuclei can cause negative climate forcing (Sporre et al. 2019). ...
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We studied responses of needle terpene concentrations and resin canal characteristics to warming in Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) seedlings grown in a controlled field set-up in eastern Finland. Warming was simulated during the growing seasons using infrared heaters that increased air temperature in study 1 (2016–2019) by 1 °C and in study 2 (2019–2020) by 2 and 4 °C, compared to ambient conditions. Terpenes were sampled in study 1 from non-matured current year and matured previous year needles in June 2019, and study 2 from mature current year needles in August 2020. In study 1, we also studied resin canal anatomy. We found that 1 °C elevation of temperature caused two-fold increase in concentrations of total terpenes, oxygenated monoterpenes, and sesquiterpenes of non-matured current year needles of Norway spruce. Further, it caused 1.3–1.8-fold increases in sesquiterpene concentrations both in unmatured and matured needles of Scots pine. It also decreased resin canal diameter of mature needles in Norway spruce. In study 2, the stronger warming treatments did not affect terpene concentrations of matured current year needles in either species. Based on our findings, even minor elevation of temperature may affect terpene concentrations of non-mature needles in boreal conifers.
... These emissions have received considerable attention due to the fact that most of them are highly reactive and thus affect atmospheric chemistry to a greater extent than comparable amounts of organic pollutants from industrial and motor vehicle emissions (Bell and Ellis, 2004). In the atmosphere, VOCs undergo gas-phase oxidation (Atkinson and Arey, 2003) or photostimulated oxidation on the surface of solid atmospheric aerosols (Isidorov, 1992: Isidorov et al., 1997. Their reactions with q OH radicals and NO x result in the production of secondary photooxidants, such as ozone, H 2 O 2 , ROOH and peroxyacetyl nitrate (PAN). ...
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Plant litter decomposition is a biogeochemical process underlying the carbon cycle in terrestrial ecosystems and between the biosphere and the atmosphere. For the latter, it serves as one of the most important sources of not only carbon dioxide but also volatile organic compounds (VOCs), which have not yet been taken into account in atmospheric models for various purposes and scales, from local to regional and global. This review owes its appearance to the growing interest in decaying leaf litter and living forest floor cover as a hitherto unaccounted for source of photochemically active components of the Earth's atmosphere. This interest is understandable if we take into account the size of this source: for terrestrial ecosystems, the global production of litter is 10 × 1016 g dry matter. The living vegetation cover of the soil on the forest floor, mainly comprising mosses and small shrubs, should also be regarded as a potentially significant source of atmospheric VOCs, as its total biomass may be comparable to or even exceed that of canopy foliage, which is considered the main source of these compounds. This implies a need to integrate these sources into biogenic VOC emission models, which in turn requires extensive research on these sources to understand the conditions and factors that influence VOC emissions. The decomposition of leaf litter, accompanied by the release of VOCs, is a very complex process that depends on a number of biological, chemical and physical environmental factors, but little information is currently available on the role each plays. Equally limited is information on the chemical composition and emission rates of VOCs from these sources. The review focuses on the main gaps in our knowledge of the sources of biogenic VOCs under the forest canopy, and we are confident that filling them will make a significant contribution to solving such an important task as closing the global organic carbon budget.
... This value is higher than the estimated annual emissions of anthropogenic volatile organic compounds (AVOCs) (98-158 TgC) (Boucher et al. 2013). Given their high reactivity in the atmosphere (Atkinson and Arey 2003), terpenoids play a significant role in the production of photochemical oxidants, including ozone (O 3 ), and secondary organic aerosols (SOA). Tropospheric O 3 negatively affects humans, animals, and plants (Tani and Mochizuki 2021;Masui et al. 2023). ...
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Uncontrolled terpenoid emissions from forest trees in Japan may have contributed to high O 3 concentrations observed in urban and suburban areas. To estimate ozone formation via a series of reactions between NO x and terpenoids using atmospheric chemistry models, it is important to produce terpenoid emission inventories by collecting all reported emission data for the major tree species in Japan and examining their reliability. In this review, we first describe three different plant terpenoid emission types, i.e., isoprene-emitting type, monoterpene-emitting type with storage tissues and organs, and monoterpene-emitting type without storage tissues and organs. Second, we describe various methods for measuring plant terpenoid emissions, including a recently developed simplified method, and explain their reliability. We emphasized that applicable measurement methods depend on the terpenoid emission types. Data obtained using static chamber methods should not be considered because they have the highest uncertainty resulting from normal chamber materials that are not specific to terpenoid measurements and lack humidity control. Finally, we show the absolute values of the collected emission rates and describe their variability. The deciduous oak species, Quercus serrata and Quercus mongolica var. crispula, and bamboo species, Phyllostachys pubescens and Phyllostachys bambusoides, are strong isoprene emitters. Among the monoterpene emitters, four evergreen broadleaf trees, including three Quercus species, had the highest basal emission rate (BER). The monoterpene storage type conifers Larix kaempferi and Pinus densiflora have relatively lower BERs. Emission data are not available for Castanopsis cuspidata, and seasonal changes in emission rates have not been reported for several major tree species in the top 20 rankings. Within species, the reported emission rates of some tree species differed by threefold. These differences may be attributed to the reliability of the measurement and analytical systems, tree age, leaf morphology, environmental conditions, and genetic diversity. We emphasize the need for reliable measurements to achieve a more precise terpenoid emission inventory for major tree species in Japan.
... This value is higher than the estimated annual emissions of anthropogenic volatile organic compounds (AVOCs) (98-158 TgC) (Boucher et al. 2013). Given their high reactivity in the atmosphere (Atkinson and Arey 2003), terpenoids play a significant role in the production of photochemical oxidants, including ozone (O 3 ), and secondary organic aerosols (SOA). Tropospheric O 3 negatively affects humans, animals, and plants (Tani and Mochizuki 2021;Masui et al. 2023). ...
Article
Full-text available
Uncontrolled terpenoid emissions from forest trees in Japan may have contributed to high O 3 concentrations observed in urban and suburban areas. To estimate ozone formation via a series of reactions between NO x and terpenoids using atmospheric chemistry models, it is important to produce terpenoid emission inventories by collecting all reported emission data for the major tree species in Japan and examining their reliability. In this review, we first describe three different plant terpenoid emission types, i.e., isoprene-emitting type, monoterpene-emitting type with storage tissues and organs, and monoterpene-emitting type without storage tissues and organs. Second, we describe various methods for measuring plant terpenoid emissions, including a recently developed simplified method, and explain their reliability. We emphasized that applicable measurement methods depend on the terpenoid emission types. Data obtained using static chamber methods should not be considered because they have the highest uncertainty resulting from normal chamber materials that are not specific to terpenoid measurements and lack humidity control. Finally, we show the absolute values of the collected emission rates and describe their variability. The deciduous oak species, Quercus serrata and Quercus mongolica var. crispula , and bamboo species, Phyllostachys pubescens and Phyllostachys bambusoides, are strong isoprene emitters. Among the monoterpene emitters, four evergreen broadleaf trees, including three Quercus species, had the highest basal emission rate (BER). The monoterpene storage type conifers Larix kaempferi and Pinus densiflora have relatively lower BERs. Emission data are not available for Castanopsis cuspidata , and seasonal changes in emission rates have not been reported for several major tree species in the top 20 rankings. Within species, the reported emission rates of some tree species differed by threefold. These differences may be attributed to the reliability of the measurement and analytical systems, tree age, leaf morphology, environmental conditions, and genetic diversity. We emphasize the need for reliable measurements to achieve a more precise terpenoid emission inventory for major tree species in Japan.
... BVOCs have short lifetimes due to their high reactivity with the atmosphere, and most BVOCs in the atmosphere decompose in a few hours or less (Atkinson & Arey, 2003). Due to such short lifetimes, it is expected that BVOCs have a relatively short effective distance as signaling agents. ...
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Plants emit biogenic volatile organic compounds (BVOCs) as signaling molecules, playing a crucial role in inducing resistance against herbivores. Neighboring plants that eavesdrop on BVOC signals can also increase defenses against herbivores or alter growth patterns to respond to potential risks of herbivore damage. Despite the significance of BVOC emissions, the evolutionary rationales behind their release and the factors contributing to the diversity in such emissions remain poorly understood. To unravel the conditions for the evolution of BVOC emission, we developed a spatially explicit model that formalizes the evolutionary dynamics of BVOC emission and non‐emission strategies. Our model considered two effects of BVOC signaling that impact the fitness of plants: intra‐individual communication, which mitigates herbivore damage through the plant's own BVOC signaling incurring emission costs, and inter‐individual communication, which alters the influence of herbivory based on BVOC signals from other individuals without incurring emission costs. Employing two mathematical models—the lattice model and the random distribution model—we investigated how intra‐individual communication, inter‐individual communication, and spatial structure influenced the evolution of BVOC emission strategies. Our analysis revealed that the increase in intra‐individual communication promotes the evolution of the BVOC emission strategy. In contrast, the increase in inter‐individual communication effect favors cheaters who benefit from the BVOCs released from neighboring plants without bearing the costs associated with BVOC emission. Our analysis also demonstrated that the narrower the spatial scale of BVOC signaling, the higher the likelihood of BVOC evolution. This research sheds light on the intricate dynamics governing the evolution of BVOC emissions and their implications for plant–plant communication.
... Among them, terpene compounds predominate, unsaturated in their chemical nature. Their lifetime in the atmosphere is limited to a few minutes due to rapid gas-phase reactions with permanent components of the Earth's atmosphere such as OH and NO 3 radicals [48]. These processes lead to the rapid formation of toxic photo-oxidants (ozone and organic peroxides), many of which exhibit phytotoxic effects and have a negative impact on plant communities, as well as human health [49]. ...
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The decomposition of plant litter, most of which is found in forests, is an important element of the global carbon cycle, as a result of which carbon enters the atmosphere in the form of not only CO2 but also volatile organic compounds (VOCs). Although the formation of litter is associated with autumn cooling, in the spring, there is a very intense fall of faded inflorescences of woody plants. This study examined the chemical composition of the litter and VOCs emitted from decaying inflorescences of four species of forest-forming trees: silver birch, European hornbeam, black alder and aspen. All litter emissions consisted of 291 VOCs, mainly terpenes actively participating in atmospheric processes. The detection of a number of typical mushroom metabolites, such as 1-octen-3-ol, known as “mushroom alcohol”, and alkyl sulphides, suggests that inflorescence-derived VOCs are a mixture of components of plant and microbial origin. In methanol extracts of the fallen inflorescences of all types, 263 organic compounds were identified, the majority of which were related to carbohydrates. Their share in the extracts was 72–76%. In general, the composition of the extractive compounds indicates the easy availability of this material for assimilation by various types of destructors.
... 24,25 These two molecules have a lifetime between 0.5 and 3 h 23 because their crowded structure determines a high reactivity with OH, NO 3 , and O 3 , leading to the formation of secondary organic aerosols. 24,26 In order to understand the chemistry of the troposphere (concerning both composition and reactivity), it is mandatory to know accurate molecular structures. The new composite schemes mentioned above could provide this information and have been validated using the experimental information of 19 bicycle monoterpenes, whose experimental microwave (MW) spectra have been recorded, [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42] mostly in the last eight years. ...
Article
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The structural, conformational, and spectroscopic properties in the gas phase of 20 bicyclic monoterpenes and monoterpenoids have been analyzed by a new accurate, reduced-cost computational strategy. In detail, the revDSD-PBEP86 double-hybrid functional in conjunction with the D3BJ empirical dispersion corrections and a suitable triple-zeta basis set provides accurate geometrical parameters, whence equilibrium rotational constants, which are further improved by proper account of core–valence correlation. Average deviations within 0.1% between computed and experimental rotational constants are reached when taking into account the vibrational corrections obtained by the B3LYP functional in conjunction with a double-zeta basis set in the framework of second-order vibrational perturbation theory. In addition to their intrinsic interest, the studied terpenes further extend the panel of systems for which the proposed strategy has provided accurate results at density functional theory cost. Therefore, a very accurate yet robust and user-friendly tool is now available for systematic investigations of the role of stereo-electronic effects on the properties of large systems of current technological and/or biological interest by experimentally oriented researchers.
... Atmospheric degradation of NMVOCs leads to the production of CO 2 , which is a known secondary direct effect on climate change (Boucher et al., 2009). The NMVOCs participate in numerous photochemical reactions in the troposphere considered to be critical precursors of ozone, photochemical smog, and secondary organic aerosols (Atkinson and Arey, 2003). NMVOCs, through complex photochemical reactions, indirectly affect global climate change by reducing the efficiency of GHG oxidation and thus promote accumulation of GHGs in the atmosphere (Collins et al., 2002). ...
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Climate impacts of landfill gas emissions were investigated for 20- and 100-year time horizons to identify the effects of atmospheric lifetimes of short- and long-lived drivers. Direct and indirect climate impacts were determined for methane and 79 trace species. The impacts were quantified using global warming potential, GWP (direct and indirect); atmospheric degradation (direct); tropospheric ozone forming potential (indirect); secondary aerosol forming potential (indirect) and stratospheric ozone depleting potential (indirect). Effects of cover characteristics, landfill operational conditions, and season on emissions were assessed. Analysis was conducted at five operating municipal solid waste landfills in California, which collectively contained 13% of the waste in place in the state. Climate impacts were determined to be primarily due to direct emissions (99.5 to 115%) with indirect emissions contributing −15 to 0.5%. Methane emissions were 35 to 99% of the total emissions and the remainder mainly greenhouse gases (hydro)chlorofluorocarbons (up to 42% of total emissions) and nitrous oxide. Cover types affected emissions, where the highest emissions were generally from intermediate covers with the largest relative landfill surface areas. Landfill-specific direct emissions varied between 683 and 103,411 and between 381 and 37,925 Mg CO2-eq./yr for 20- and 100-yr time horizons, respectively. Total emissions (direct + indirect) were 680 to 103,600 (20-yr) and were 374 to 38,108 (100-yr) Mg CO2-eq./yr. Analysis time horizon significantly affected emissions. The 20-yr direct and total emissions were consistently higher than the 100-yr emissions by up to 2.5 times. Detailed analysis of time-dependent climate effects can inform strategies to mitigate climate change impacts of landfill gas emissions.
... Although some VOCs including biogenic monoterpenes have beneficial effects on human health (Cho et al., 2017), most other VOCs have negative effects on human and atmosphere. VOCs promote the generation of photochemical oxidants, including ozone (Atkinson and Arey, 2003;Sillman, 1999), that degrade air quality. VOCs can also promote the production of secondary organic aerosols that affect the climate and degrade air quality (Shrivastava et al., 2017). ...
... Formulae, structures, and reaction rate constants for OH and O 3 reacting with the acyclic terpene precursors selected in this study, as well as a benchmark terpene, a-pinene23,[47][48][49][50] ...
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Organic aerosol formed from ocimene photooxidation has more oligomers compared to organic aerosol formed from other acyclic terpene precursors.
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Climate change will bring about changes in meteorological and ecological factors that are currently used in global-scale models to calculate biogenic emissions. By comparing long-term datasets of biogenic compounds to modeled emissions, this work seeks to improve understanding of these models and their driving factors. We compare speciated biogenic volatile organic compound (BVOC) measurements at the Virginia Forest Research Laboratory located in Fluvanna County, VA, USA, for the year 2020 with emissions estimated by the Model of Emissions of Gases and Aerosols from Nature version 3.2 (MEGANv3.2). The emissions were subjected to oxidation in a 0-D box model (F0AM v4.3) to generate time series of modeled concentrations. We find that default light-dependent fractions (LDFs) in the emissions model do not accurately represent observed temporal variability in regional observations. Some monoterpenes with a default light dependence are better represented using light-independent emissions throughout the year (LDFα-pinene=0, as opposed to 0.6), while others are best represented using a seasonally or temporally dependent light dependence. For example, limonene has the highest correlation between modeled and measured concentrations using an LDF =0 for January through April and roughly 0.74–0.97 in the summer months, in contrast to the default value of 0.4. The monoterpenes β-thujene, sabinene, and γ-terpinene similarly have an LDF that varies throughout the year, with light-dependent behavior in summer, while camphene and α-fenchene follow light-independent behavior throughout the year. Simulations of most compounds are consistently underpredicted in the winter months compared to observed concentrations. In contrast, day-to-day variability in the concentrations during summer months are relatively well captured using the coupled emissions–chemistry model constrained by regional concentrations of NOX and O3.
Article
Biogenic volatile organic compounds are emitted by plants and influence human and environmental health. They contribute to the formation of pollutants such as ozone and secondary organic aerosols, thereby influencing air quality and climate. Here we review biogenic volatile organic compounds with focus on biosynthesis, release to the atmosphere, distribution at various scales, tropospheric chemical processes, and secondary organic aerosols. Biogenic volatile organic compounds are emitted primarily through enzymatic pathways in response to environmental factors, varying across plant species and ecosystems. These emissions exhibit heterogeneity at multiple scales, influenced by meteorological conditions and plant structure.
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Methyl vinyl ketone oxide (MVKO, C2H3C(CH3)OO) is an important Criegee intermediate produced from ozonolysis of isoprene, which is the most abundant nonmethane hydrocarbon emitted into the atmosphere. Reactions between Criegee intermediate and hydrogen chloride (HCl) are important because of their large rate coefficients. In this work, we photolyzed a mixture of (Z)-(CH2I)HC=C(CH3)I/HCl/O2 at 248 nm to produce MVKO to carry out the reaction MVKO + HCl and recorded infrared spectra of transient species with a step-scan Fourier-transform infrared absorption spectrometer. Eleven bands near 1415, 1381, 1350, 1249, 1178, 1118, 1103, 1065, 978, 931, and 895 cm–1 were observed and assigned to the hydrogen-transferred adduct (C2H3)CCl(CH3)OOH (2-chloro-2-hydroperoxybut-3-ene, CHPB) according to the predicted IR spectrum using the B3LYP/aug-cc-pVTZ method; the conformation could not be definitively determined. According to calculations, most low-energy conformers can interconvert, and the most stable conformers anti–trans-CHPB and syn–trans-CHPB might have the major contributions. Four bands near 1423, 1360, 1220, and 1080 cm–1 were observed and tentatively assigned to the OH-decomposition products (C2H3)CCl(CH3)O (1-chloro-1-methyl-2-propenyloxy, CMP); both trans-CMP and cis-CMP might contribute. Unlike in the case of CH2OO + HCl and CH3CHOO + HCl, in which secondary reactions of the OH-decomposition products reacted readily with O2 to produce the dehydrated products HC(O)Cl and CH3C(O)Cl, respectively, the secondary reaction of CMP with O2 was not observed because there is no feasible H atom in CMP for O2 to abstract.
Preprint
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Aerosols play an important role in atmospheric processes influencing cloud formation, scattering and absorbing solar radiation, and as a part of the chemical reactions affecting the abundance of trace gases in the atmosphere. Ultimately aerosols affect the radiative balance of the earth modifying climate. A large fraction of aerosols is formed through chemical reactions following gas-to-particulate processes in the atmosphere: nucleation, condensation and growth. Biogenic Secondary Organic Aerosols (BSOA) are formed when plant produced volatile organic compounds (VOCs) react in the atmosphere through heterogeneous reactions. South-east Australia is one of the locations with the highest emissions of biogenic VOCs in the world, due to the high density of Eucalyptus species, which are high emitters of VOCs. The COALA-2020 (Characterizing Organics and Aerosol Loading over Australia) campaign worked towards a better understanding of biogenic VOCs in quasi-pristine conditions in the atmosphere and their role in particle formation. The observations showed a highly reactive atmosphere with frequent new particle formation occurring (50 % days with data) often associated with pollution plumes. Analysis of NPF events indicated that SO₂ and NOx plumes triggered particle formation, while particle growth depended on available VOCs, OH concentration (influenced by relative humidity), and the presence of multiple SO₂ and NOx intrusions promoted growth of smaller clusters. Nighttime NPF events correlated with NOx but the limited night-time data hindered conclusive interpretations. These findings highlight the significant role of biogenic VOCs, especially isoprene, in driving NPF and SOA formation in South-east Australia, even after major wildfires. The COALA-2020 campaign provided valuable insights into local atmospheric chemistry and its potential impact on regional air quality and climate. However, longer-term observations are crucial to understand seasonal variations, trends and extreme events.
Preprint
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Secondary organic aerosols (SOAs) significantly impact Earth’s climate and human health. Although the oxidation of volatile organic compounds (VOCs) has been recognized as the major contributor to the atmospheric SOA budget, the mechanisms by which this process produces SOA-forming highly oxygenated organic molecules (HOMs) remain unclear. A major challenge is navigating the complex chemical landscape of these transformations, which traditional hypothesis-driven methods fail to thoroughly investigate. Here, we explored the oxidation of α-pinene, a critical atmospheric biogenic VOC, using a novel reaction discovery approach based on ab initio molecular dynamics and state-of-the-art enhanced sampling techniques. Our approach successfully identified all established reaction pathways of α-pinene ozonolysis, as well as discovered multiple novel species and pathways without relying on a priori chemical knowledge. In particular, we unveiled an unexpected branching point that leads to the rapid formation of alkoxy radicals, whose high and diverse reactivity help to explain hitherto unexplained oxidation pathways suggested by mass spectral peaks observed in α-pinene ozonolysis experiments. This branching point is likely prevalent across a variety of atmospheric VOCs and could be crucial in establishing the missing link to SOA-forming HOMs.
Preprint
Full-text available
Climate change will bring about changes in meteorological and ecological factors that are currently used in global-scale models to calculate biogenic emissions. By comparing long-term datasets of biogenic compounds to modeled emissions, this work seeks to improve understanding of these models and their driving factors. We compare speciated BVOC measurements at the Virginia Forest Research Laboratory located in Fluvanna County, VA, USA for the 2020 year with emissions estimated by MEGANv3.2. The emissions were subjected to oxidation in a 0-D box-model (F0AM v4.3) to generate timeseries of modeled concentrations. We find that default light-dependent fractions (LDFs) in the emissions model do not accurately represent observed temporal variability of regional observations. Some monoterpenes with a default light dependence are better represented using light-independent emissions throughout the year (LDFα-pinene=0, as opposed to 0.6), while others are best represented using a seasonally or temporally dependent light dependence. For example, limonene has the highest correlation between modeled and measured concentrations using LDF=0 for January through April and roughly 0.74–0.97 in the summer months, in contrast to the default value of 0.4. The monoterpenes β-thujene, sabinene, and γ-terpinene similarly have an LDF that varies throughout the year, with light-dependent behavior in summer, while camphene and α-fenchene follow light-independent behavior throughout the year. Simulations of most compounds are consistently underpredicted in the winter months compared to observed concentrations. In contrast, day-to-day variability in the concentrations during summer months are relatively well captured using the coupled emissions-chemistry model constrained by regional concentrations of NOx and O3.
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In the troposphere, {alpha}-pinene, {beta}-pinene, limonene, and linalool are mainly oxidized to pinonaldehyde, nopinone, 3-isopropenyl-6-oxoheptanal (IPOH), and 5-methyl-5-vinyltetrahydrofuran-2-ol (MVT), respectively. The rate constant of the reactions of nopinone, IPOH, and MVT with OH, NO{sub 3}, and O{sub 3} were determined by long path FT-IR spectroscopy, and the oxidation products from the reactions between the OH radical and pinonaldehyde, nopinone, IPOH, and MVT were investigated using GC-MS and HPLC. The reaction rate constants (k) for the reactions have been determined at 740 {+-} 5 Torr and 298 {+-} 5 K, and a number of reaction products were identified. From the results obtained in this investigation and previous studies, it was concluded that a typical atmospheric lifetime with respect to chemical reactions was only a few hours for pinonaldehyde, IPOH, and MVT but was much longer for nopinone with a lifetime of about 10 h.
Article
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The reactions of ozone with alkenes have been shown recently to lead to the direct production of OH radicals. Organic peroxy radicals (RO2) probably accompany the production of OH. In this paper, we draw attention to the potential importance of these reactions in the primary production of HOx (HOx = OH, HO2 and RO2) radicals in various regions of the boundary layer. The reactions of ozone with anthropogenic alkenes are shown to be the most important source of HOx in many urban settings during the day and evening, and a significant source at night. The majority of HOx comes from trace quantities of alkenes with internal double bonds. Reaction of O3 with isoprene and terpenes can be an important source of HOx in forested regions; we show that these reactions are the dominant radical source in the late afternoon and into the night. This additional HOx source is expected to increase predicted OH concentrations compared to those calculated by models that do not include the O3-alkene source.
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OH radical formation from the ozone reaction with isoprene, alpha-pinene, and methyl vinyl ketone were measured using the recently developed small-ratio relative-rate technique. This method uses small amounts of fast-reacting aromatics and aliphatic ethers to trace OH formation. Measured OH yields were 0.25+/-0.06, 0.70+/-0.17, and 0.16+/-0.05 for isoprene, alpha-pinene, and methyl vinyl ketone, respectively. The levels of biogenic alkenes necessary to contribute a non-negligible fraction of new OH, HO2, and RO2 radicals are briefly discussed.
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This paper updates and extends part of the previous data base of critical evaluations of the kinetics and photochemistry of gas-phase chemical reactions of neutral species involved in atmospheric chemistry [J. Phys. Chem. Ref. Data 9, 295 (1980); 11, 327 (1982); 13, 1259 (1984); 18, 881 (1989); 21, 1125 (1992); 26, 521 (1997); 26, 1329 (1997)]. The present evaluation is limited to the organic family of atmospherically important reactions. The work has been carried out by the authors under the auspices of the IUPAC Subcommittee on Gas Phase Kinetic Data Evaluation for Atmospheric Chemistry. Data sheets have been prepared for 171 thermal and photochemical reactions, containing summaries of the available experimental data with notes giving details of the experimental procedures. For each thermal reaction, a preferred value of the rate coefficient at 298 K is given together with a temperature dependence where possible. The selection of the preferred value is discussed and estimates of the accuracies of the rate coefficients and temperature coefficients have been made for each reaction. For each photochemical reaction the data sheets list the preferred values of the photoabsorption cross sections and the quantum yields of the photochemical reactions together with comments on how they were selected. The data sheets are intended to provide the basic physical chemical data needed as input for calculations which model atmospheric chemistry. A table summarizing the preferred rate data is provided, together with an Appendix listing the available values of enthalpies of formation of the reactant and product species.
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The reactions of alpha-pinene and of its main oxidation product, pinonaldehyde (3-acetyl-2,2-dimethyl-cyclobutyl-ethanal), with OH radicals have been studied in the laboratory using Fourier transform infrared spectroscopy for real-time monitoring of the gas-phase chemical species and a Scanning Mobility Particle Sizer system (3071 A, TSI) for the study of the secondary aerosol formation. All gas-phase molar yields were quantified using calibrated reference of the pure compound, except for the nitrates products. The results were: for the alpha-pinene experiments in the presence of NOx, pinonaldehyde, (87+/-20)% total nitrates (18+/-9)% formaldehyde, (23+/-9)% acetone (9+/-6)% for the alpha-pinene experiments in the absence of NOx: pinonaldehyde, (37+/-7)% formaldehyde, (8+/-1)% acetone, (7+/-2)% for the pinonaldehyde experiments in the presence of NO, formaldehyde (152+/-56)% and acetone (15+/-7)%. The aerosol measurements showed that the condensed products accounted for the missing carbon in the gas-phase balance. The partitioning of the products into the condensed phase was found to be potentially significant under experimental conditions but less than 10% for initial alpha-pinene concentrations lower than 1013 molecule cm-3 and hence negligible under atmospheric conditions in the absence of aerosol seeds. On the basis of these results a comprehensive mechanism for the gas-phase reaction of alpha-pinene with OH in the presence of NOx has been proposed, including quantitative values for all the involved branching ratios.
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Biogenic volatile organic compounds (BVOC) were measured at Azusa and at either Pine Mountain or Mount Baldy, elevated sites 11 km north and 25 km northeast of Azusa, respectively, during four intensive sampling periods of the 1997 Southern California Ozone Study. During the sampling periods there was a consistent pattern of isolation of the mountain sites from valley air masses at night, followed by transport of valley air with elevated levels of O3 and NOx to the mountain sites as the mixing height increased throughout the day. Isoprene was the dominant BVOC at the mountain sites with afternoon concentrations reaching 2 ppbv, and its decrease to a low mixing ratio after sunset was attributed to reaction with NO3 radicals. At Azusa the BVOC mixing ratios were highest in the morning with the concentrations of monoterpenes and of methacrolein (MACR) and methyl vinyl ketone (MVK), isoprene photooxidation products, generally exceeding the maximum isoprene measured at Azusa. The high daytime ratio of (MVK+MACR)/isoprene suggested that nighttime drainage flows into Azusa, from elevated sites where the isoprene was depleted by chemical reaction, may have been responsible for much of the isoprene and its photoxidation products. The data also indicated local isoprene sources at Azusa and a possible contribution of MVK and MACR from vehicle emissions. Instances of high mixing ratios of limonene at Azusa suggested an intermittent anthropogenic source. During this study, particularly in early morning, BVOC are calculated to make a significant contribution to peroxy radical formation at Azusa.
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The first evidence and laboratory study of a peroxyacetyl nitrate (PAN) analogue produced by the photooxidation of a terpene, alpha-pinene, is presented. This PAN analogue, assigned to 3-acetyl-2,2-dimethyl-cyclobutane-acetyl peroxynitrate and referred to as ``alpha-pinonyl peroxynitrate'' (alphaP-PAN) was synthesized in the gas phase from the radical (OH, Cl, Br, or NO3) initiated oxidation of pinonaldehyde (3-acetyl-2,2-dimethyl-cyclobutyl-ethanal) in the presence of excess NO2 and evidenced by Fourier transform-infrared (FT-IR) spectroscopy. Another reaction channel producing PAN was also observed for some of the radical initiators. Of particular atmospheric interest, the experiments with OH radicals demonstrated that alphaP-PAN is the main product of pinonaldehyde under NOx-rich conditions with a yield of (81.3+/-16)%, while an upper limit of the PAN yield for this reaction is around 8%. The further photooxidation of alphaP-PAN was also observed to produce PAN directly. The thermal stability of alphaP-PAN was studied between 303 and 281 K. The rate constant of thermal dissociation was found to be k-1=10(9.25+/-0.33)×exp[-(72.0+/-1.9)/RT] where the activation energy is in kJmol-1. Distortions of the kinetic profiles attributed to aerosol formation were observed and led to large errors in the above estimation of k-1. Within the uncertainties, the observed thermal stability of alphaP-PAN is comparable to that of PAN. The tropospheric importance of pinonaldehyde and of alphaP-PAN are discussed.
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Isoprene and its oxidation products, methyl vinyl ketone (MVK) and methacrolein (MACR), were measured in a semirural environment that was occasionally heavily impacted by urban emissions. At this site, isoprene was the most important hydrocarbon in terms of kOH.[hydrocarbon], but the aldehydes HCHO and CH3CHO also appear to be very important. The local isoprene photochemistry appears to be occasionally enhanced in NOx-rich urban plumes that are advected to the site over intermediate forested land. When O3 was being rapidly produced in urban plumes advected to this forested site, isoprene was found to contribute ~28% of the total ozone production. We observe that many of the peaks in isoprene oxidation products at this surface site arise from downward mixing of more photochemically processed air aloft, as the nocturnal inversion breaks up in the morning. We estimate that, in the daytime, typically 1-2% of the NOy at this NOx-rich site is composed of isoprene nitrates.
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Reactions between ozone and alpha-pinene and beta-pinene are examined to obtain quantitative yields of gaseous and particulate products. The gaseous products from alpha-pinene include CO, CO2, HCHO, and aldehydes composed of pinonaldehyde and nor-pinonaldehyde. The beta-pinene gaseous products are CO2, HCHO, and 6,6-dimethylbicyclo(3.1.1)heptan-2-one. The average molar yields of these products are presented. The particulate products from alpha-pinene include pinonaldehyde, nor-pinonaldehyde, pinonic acid, and nor-pinonic acid. The results suggest the sequential oxidation of aldehydes to carboxylic acids. From beta-pinene, the only particulate product was 6,6-dimethylbicyclo(3.1.1)heptan-2-one. The emission rate of CO from the ozone reactions with terpenes is discussed.
Book
This text reviews many of the aspects of the chemistry of the aromatic hydrocarbons and a consensus evaluation of the data by seven of the leading atmospheric scientists. The book covers topics ranging from the relative importance of the compounds in ozone and haze development to methods of estimating elemantary rate coefficients based on structural features of the compounds to mechanisms of aerosol generation and atmostpheric reaction of the polycyclic compounds to photochemical processes. It identifies features of the aromatic hydrocarbons requiring further study and appendicies give the structural formulas and nomenclature of the compounds reviewed in the book.
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The OH radical yields generated in the ozonolysis of ethene (ET), propene (PR), cis-2-butene (CB), trans-2-butene (TB), 2,3-dimethyl-2-butene (TME), and isoprene (ISP) in the presence of 20 Vol.% O2 have been determined in a darkened glass reactor at 1 bar total pressure. The hydroxyl radicals formed were scavenged by an excess of CO added to the systems. The O2 present converted H atoms formed in this reaction into HO2. From measurements of the increase in CO2 generation by FTIR the OH formation yields were determined to be 0.08 (ET), 0.18 (PR), 0.17 (CB), 0.24 (TB), 0.36 (TME), and 0.19 (ISP), respectively, per molecule of reacted ozone. The combined error in the OH determinations is estimated to be <10%. © 1997 John Wiley & Sons, Inc.
Article
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Article
6-Methyl-5-hepten-2-one is an atmospheric reaction product of the biogenic emission linalool, and trans-cinnamaldehyde is a model compound for dicarbonyls formed from the OH radical-initiated reaction of naphthalene. These carbonyl compounds react in the atmosphere, and photolysis and the gas-phase reactions of 6-methyl-5-hepten-2-one and trans-cinnamaldehyde with OH radicals, NO3 radicals, and O3 have been investigated at 296 ± 2 K and atmospheric pressure of air. Using relative rate methods, the respective rate constants obtained for the OH radical, NO3 radical, and O3 reactions were (in cm3 molecule-1 s-1 units) as follows: for 6-methyl-5-hepten-2-one: (1.57 ± 0.39) × 10-10, (7.5 ± 3.0) × 10-12, and (3.9 ± 1.5) × 10-16;for trans-cinnamaldehyde: (4.8 ± 1.4) × 10-11, (1.9 ± 0.7) × 10-14, and (2.2 ± 1.8) × 10-18. trans-Cinnamaldehyde was also observed to photolyze. Benzaldehyde was observed and quantified from the OH radical reaction with trans-cinnamaldehyde, with a yield of 0.90 ± 0.39. Acetone and CH3C(O)CH2CH2CHO were observed and quantified from the OH radical and O3 reactions with 6-methyl-5-hepten-2-one, with formation yields of 0.706 ± 0.054 and 0.59 ± 0.13, respectively, from the OH radical reaction and 0.302 ± 0.048 and 0.82 ± 0.21, respectively, from the O3 reaction. The reaction mechanisms are discussed.
Chapter
The biosphere, especially vegetation, releases a complex mixture of volatile organic compounds (VOCs) into the atmosphere. Some of these biogenic VOCs are emitted in surprisingly large amounts and have high enough chemical reactivity to significantly affect the chemistry of the atmosphere. Most living systems directly or indirectly exchange volatile chemical compounds with the atmosphere. Over biological time, the major gases exchanged with living organisms have included carbon dioxide, with production by respiring organisms and uptake by photosynthetic and chemoautotrophic organisms; oxygen (O2), with production by photosynthetic organisms and uptake by aerobic respiration; and nitrogen (N2), which is produced by denitrifying bacteria and taken up by nitrogen-fixing bacteria. This chapter describes the major biogenic VOCs emitted by higher plants and the mechanisms of their formation. In addition, the chapter describes the regulation and roles of formation of VOCs and their emission from plant surfaces. The details of these biochemical and biological processes are complex, comparable in complexity to the photochemistry of VOCs in the atmosphere, but need to be appreciated to accurately model regional and global biogenic VOC emissions.
Article
A method for the analysis of carboxylic acids in aerosols was developed, based on the collection of particles on Teflon filters (2.5 cm diameter with a 0.4 μm pore size), extraction with dichloromethane, and derivatization with BF3-methanol followed by analysis of the formed methylesters by large-volume injection GC/MS. In aerosol samples from smog chamber experiments with α-pinene and ozone, this method was applied and resulted in the identification for the first time of cis-pinic acid. Yields were in the range of 1-3% for 1000 pbbv α-pinene reacted with 750 pbbv ozone, and in in the range of 0.3-0.5% for 100 pbbv α-pinene reacted with 75 pbbv ozone. Being a dicarboxylic acid this product is estimated to possess an extremely low vapour pressure and may thus be an important element in gas-to-particle conversion of α-pinene.
Article
In a recent field study, strong indications have been obtained that 2-methyl-3-buten-2-ol (methyl butenol, MBO) is a compound emitted in important quantities by some types of vegetation. The atmospheric oxidation products from MBO are not yet well known. In this investigation we studied the reaction mechanisms and products of the reaction of MBO with OH radicals, O3 and NO3 radicals. All the experiments were performed in a 480 ℓ Teflon coated Pyrex glass chamber equipped with a long path length FTIR spectrometer. As products from the reaction between MBO and OH we identified and quantified acetone, glycolaldehyde, formaldehyde, formic acid, CO and CO2. From the reaction between MBO and O3, the products acetone, formaldehyde, formic acid, CO and CO2 have been identified; also, 2-hydroxy-2-methyl-propanal (HMPR) is tentatively put forward as a product on the basis of HPLC and GC-MS analysis of the DNPH derivative. Organic nitrates, peroxynitrates and carbonyl nitrates, together with acetone were observed as products of the reaction between MBO and the nitrate radical. Tentative reaction mechanisms for the oxidation of MBO by OH radicals, O3 and NO3 radicals are proposed.
Article
The formation yields of acetone from the gas-phase reactions of the OH radical (in the presence of NO) and O3 with a series of monoterpenes have been measured at room temperature and atmospheric pressure of air. The acetone formation yields ranged from <2-3% for the OH radical reaction with limonene and the O3 reactions with limonene and α-phellandrene to 50% for the O3 reaction with terpinolene. Combining these acetone formation yields with literature estimates of emission rates of monoterpenes from vegetation leads to an estimate of acetone formation from the atmospheric photooxidation of monoterpenes of ∼10-11 Tg yr-1 globally, a significant fraction of the global acetone source strength of 40-60 Tg yr-1. Reaction mechanisms leading to acetone formation from these monoterpene reactions are discussed.
Article
Rate constants for the gas-phase reactions of OH and NO3 radicals with the biogenically emitted monoterpenes 2-carene and terpinolene and the related compounds 1,8-cineole and p-cymene have been determined at 295 ± 2 K and atmospheric pressure by using relative rate methods. The rate constants obtained were (cm3 molecule-1 s-1) as follows. For reaction with the OH radical: 2-carene, 7.95 x 10-11; 1,8-cineole, 1.11 x 10-11; p-cymene, 1.51 x 10-11; terpinolene, 2.25 x 10-10. For reaction with the NO3 radical: 2-carene, 1.94 x 10-11; 1,8-cineole, 1.7 x 10-16; p-cymene, 9.9 x 10-16; terpinolene, 9.62 x 10-11. Combined with the rate data for the corresponding reactions of these compounds with O2 and the ambient tropospheric concentrations of OH and NO3 radicals and O3, these data show that the OH and NO3 radical and O3 reactions must all be considered as loss processes for 3-carene and terpinolene, with calculated lifetimes of 2-carene and terpinolene of 2 h or less. For 1,8-cineole and p-cymene, only the OH radical reactions will of importance, with tropospheric lifetimes of 1,8-cineole and p-cymene of 1.0-1.4 days being calculated.
Article
Atmospheric free radicals hydroxyl and hydroperoxyl (OH and HO2, collectively HOx) are the catalysts that cause secondary or photochemical air pollution. Chemical mechanisms for oxidant and acid formation, on which expensive air pollution control strategies are based, must accurately predict these radical concentrations. We have used the fluorescence assay with gas expansion (FAGE) technique to carry out the first simultaneous, in situ measurements of these two radicals in highly polluted air during the Los Angeles Free Radical Experiment. A complete suite of ancillary measurements was also made, including speciated hydrocarbons, carbon monoxide, aldehydes, nitric oxide, nitrogen dioxide, and ozone along with meteorological parameters. Using this suite of measurements, we tested the ability of a lumped chemical mechanism to accurately predict radical concentrations in polluted air. Comparison of model predictions with measured radical concentrations revealed generally good agreement for OH early and late in the day, including the early evening hours, when OH persisted at low concentrations after dark. During midday, however, modeled [OH] was high by about 50%. Agreement for HO2 was quite good in the early morning hours, but model-calculated HO2 concentrations were significantly too high during midday. When we used our measured HO2 concentrations as model input, agreement between calculated and measured OH concentrations was improved. It seems likely that (1) the model's HOx sources are too large, (2) there are unaccounted HOx loss processes in Los Angeles air, and/or (3) the complex parameterization of RO2/HO2 radical chemistry in the reaction mechanism does not adequately describe the behavior of these radicals in the Los Angeles atmosphere.
Article
Aerosol formation from alpha-pinene and beta-pinene was studied in a series of outdoor smog chamber experiments. The initial hydrocarbon and NO(x) concentrations ranged from 37 to 582 ppb and 31 to 380 ppb, respectively. The aerosol carbon yield, the fraction of the carbon initially present that is converted to aerosol, varied from 0 to 5.3 percent for alpha-pinene, depending on the initial hydrocarbon-to-NO(x) ratio. Dual-bag experiments demonstrate that alpha-pinene is more rapidly photooxidized, and produces higher yields of both aerosol and ozone in a given period of time than beta-pinene, although given sufficient time, beta-pinene can produce equivalent aerosol yields. The addition of isoprene to the alpha-pinene/NO(x) system leads to an increased aerosol yield through the enhanced photochemical activity generated.
Article
Hydroxyl radical yields are reported for the gas-phase ozonolyses of a range of alkenes. 1,3,5-Trimethylbenzene was employed as an OH tracer, and the diminution in its concentration was used to calculate OH yields by both a simple analytical kinetic expression and a numerically integrated model. The following OH yields were obtained, relative to alkene consumed: ethene (0.14), propene (0.32), 2-methylpropene (0.60), 2,3-dimethyl-2-butene (0.89), isoprene (0.44), {beta}-pinene (0.24), and {alpha}-pinene (0.83). A structure activity relationship (SAR) is presented for the estimation of OH yields based on structural moieties and reaction branching ratios. Reaction stoichiometries ({Delta}[alkene]/{Delta}[ozone]) are also reported, along with primary carbonyl yields measured in the presence and absence of excess SO{sub 2}, both under OH-free conditions. Reaction stoichiometries are shown to be correlated with alkene OH yields, and the mechanistic implications of this observation are discussed. The fractional increase in primary carbonyl yield in the presence of excess SO{sub 2} is shown to be inversely related to the OH yield and is interpreted as a measure of the fraction of the vibrationally excited Criegee intermediate that is stabilized in air at a pressure of 1 atm.
Article
Rate constants for the reactions of NOâ with a number of aliphatic mono- and dialkenes and monoterpenes have been determined in a 420 1 reaction chamber at 1-bar total pressure of synthetic air by 298 K with a relative kinetic method. The products of these reactions have been investigated also at 1-bar total pressure of synthetic air with in situ FT-IR spectrometry and gas chromatography. In all cases, the initial formation of thermally unstable nitrooxy-peroxynitrate-type compounds containing the difunctional group -CH(OONOâ)-CH(ONOâ)- has been observed.
Article
Products of the gas phase reactions of the OH radical with alpha- and beta-pinene in the presence of NO have been investigated using gas chromatography and in situ atmospheric pressure ionization mass spectrometry (API-MS). Acetone was identified and quantified by gas chromatography with flame ionization detection and combined gas chromatography-mass spectrometry, with formation yields of 0.110+/-0.027 from the alpha-pinene reaction and 0.085+/-0.018 from the beta-pinene reaction. Acetone is a first-generation product and may arise after initial H atom abstraction from the tertiary allylic C-H bond at the 1 position and/or after OH radical addition at the 2 and 3 positions. Using API-MS and API-MS/MS analyses, in addition to the formation of pinonaldehyde from alpha-pinene and nopinone from beta-pinene, we have observed the formation of hydroxynitrates, dihydroxynitrates and dihydroxycarbonyl products of molecular weights 215, 231 and 184, respectively, from both alpha- and beta-pinene. Reaction schemes leading to the formation of these multifunctional product species, consistent with our understanding of the atmospheric chemistry of organic peroxy and alkoxy radicals, are presented.
Article
Isoprene and its oxidation products methyl vinyl ketone (MVK) and methacrolein (MACR) were measured over a 4 week period in July of 1995 at a rural/forest site near Nashville, Tennessee, as part of the 1995 Southern Oxidants Study (SOS) field intensive. High nighttime isoprene mixing ratios, measured during a 3 day period of stagnant high pressure, are reported. These high nighttime isoprene events are interpreted as a result of continuing emission of isoprene into a developing shallow nocturnal boundary layer in the early evening, followed by advective transport under the inversion to the measurement site. During some evenings, there is very rapid decay of isoprene just after sunset. These events occurred when the product [O3].[NO2] was relatively large, consistent with loss via reaction with NO3. A chemical box model showed that isoprene decays were consistent with the NO3 mechanism but only for relatively high NOx conditions. This study indicates that nighttime processing of isoprene can be important for forested regions susceptible to high-NOx transport events. We also find that this nighttime NO3 chemistry can lead to conditions where, at least at the surface, a significant fraction of the NOy is in the form of organic nitrates that are products of the NO3-isoprene reaction and that the NO3-isoprene reaction can be the dominant NO3 sink.
Article
Products of the gas-phase reaction of alpha-pinene with OH radicals in the presence of NO have been investigated using gas chromatography with flame ionization detection to quantify pinonaldehyde and in situ atmospheric pressure ionization mass spectrometry in the negative ion mode to quantify selected other products as their NO2- adducts by utilizing C6-dihydroxycarbonyls and C6-hydroxynitrates formed in situ from the reaction of OH radicals with 1-hexene as an internal standard. The products quantified, and their molar formation yields, were: pinonaldehyde, 28 +/- 5% molecular weight 184 product (dihydroxycarbonyl), 19% (with an estimated uncertainty of a factor of ~2) molecular weight 200 product, 11% (with an estimated uncertainty of a factor of ~2). Together with a very approximate yield from our API-MS analyses for the formation of organic nitrates (~1%) and literature data for acetone (plus coproducts), ~65-70% of the reaction products and pathways are accounted for.
Article
We have investigated products formed from the gas-phase reactions of OH radicals and O3 (at 296 ± 2 K and 740 Torr total pressure of purified air) with the biogenic organic compounds myrcene and ocimene, using gas chromatographic analyses. In addition to the formation of acetone the OH radical reaction with myrcene in the presence of NO resulted in the formation of 4-vinyl-4-pentenal in 19 ± 4% yield, while the corresponding ocimene reaction showed no formation of the analogous product 4-methyl-3,5-hexadienal (
Article
Carbonyl products have been identified and their formation yields measured in the gas phase reaction of ozone with unsaturated oxygenates in experiments carried out at ambient T, p = 1 atm. of purified humid air (RH = 50%) and with sufficient cyclohexane added to scavenge the hydroxyl radical. The compounds studied are the esters methyl acrylate, vinyl acetate and cis-3-hexenyl acetate, the carbonyl crotonaldehyde, the hydroxy-substituted diene linalool, the ether ethylvinyl ether and the keto-ether trans-4-methoxy-3-buten-2-one. The alkene 1-pentene was included for comparison. The nature and formation yields of the carbonyl products from this study and those measured in earlier work under the same conditions are compared to those of alkenes and are supportive of a reaction mechanism that is similar to that for the reaction of ozone with alkenes, i.e. O3 + R1R2C=CR3X ? a(R1COR2 + R3XCOO) + (1 - a)(R3COX + R1R2COO), where Ri are the alkyl substituents, X is the oxygen-containing substituent (–CHO for aldehydes; –C(O)R for ketones; –C(O)OR and –OC(O)R for esters; –OH and hydroxyalkyl for alcohols; and –OR for ethers), R1COR2 is the primary carbonyl, R3COX is the other primary product and R1R2COO and R3XCOO are the carbonyl oxide biradicals. The biradicals lead to carbonyls in reactions that are also analogous to those involved in carbonyl formation from biradicals in the ozone-alkene reaction. These features make it possible to predict the nature and formation yields of the major carbonyl products of the reaction of ozone with unsaturated oxygenates that may be components of biogenic emissions.
Article
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Article
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Article
We present direct, pressure-dependent measurements of OH yields from gas-phase ozone-alkene reactions, using the Harvard HOx instrument to obtain sensitive, accurate, and precise OH concentrations. As in previous studies from our laboratory, steady-state [OH] is measured by laser-induced fluorescence (LIF); here, the accurate LIF calibration allows us to present absolute OH yields for the first time. To calibrate our original LIF system, we measure yields from ozone plus tetramethylethylene (TME) as a function of pressure. The pressure dependence agrees with our previous results, so our yield measurements are now of comparable accuracy to those from indirect studies. Prompt, low-pressure yields agree well with 1 atm yields measured over longer timescales, confirming that much of the OH arises from decomposition of stabilized carbonyl oxides. We also explore the pressure dependence of yields from ethene, isobutene, and isoprene. Yields from isobutene and isoprene are pressure-dependent, consistent with the formation of substituted carbonyl oxides. We observe no pressure dependence of the OH yield from ozone + ethene, finding instead a constant yield of 14%, in line with most 1 atm studies but in contrast with the results of another pressure-dependent study.
Article
The OH-initiated oxidation of methacrolein, a major product of isoprene oxidation, has been studied in an environmental chamber using FT-IR spectroscopy. Products observed (which account for more than 90% of the reacted carbon) were CO, CO2, hydroxyacetone, formaldehyde, and methacryloylperoxynitrate (MPAN). It is determined that the attack of OH on methacrolein occurs 55% of the time via addition to the double bond, and 45% via abstraction of the aldehydic hydrogen atom, in agreement with a previous study. The end products of the abstraction channel are identified and quantified for the first time, and the mechanism of their production discussed.
Article
A series of outdoor chamber experiments has been used to establish and characterize the significant atmospheric aerosol-forming potentials of the most prevalent biogenic hydrocarbons emitted by vegetation. These compounds were also studied to elucidate the effect of structure on aerosol yield for these types of compounds. Because oxidation products partition between the gas and aerosol phases, the aerosol yields of the parent biogenic hydrocarbons depend on the concentration of organic aerosol into which these products can be absorbed. For organic mass concentrations between 5 and 40 μg m−3, mass-based yields in photooxidation experiments range from 17 to 67% for sesquiterpenes, from 2 to 23% for cyclic diolefins, from 2 to 15% for bicyclic olefins, and from 2 to 6% for the acyclic triolefin ocimene. In these photooxidation experiments, hydroxyl and nitrate radicals and ozone can contribute to consumption of the parent hydrocarbon. For bicyclic olefins (α-pinene, β-pinene, Δ3-carene, and sabinene), experiments were also carried out at daytime temperatures in a dark system in the presence of ozone or nitrate radicals alone. For ozonolysis experiments, resulting aerosol yields are less dependent on organic mass concentration, when compared to full, sunlight-driven photooxidation. Nitrate radical experiments exhibit extremely high conversion to aerosol for β-pinene, sabinene, and Δ3-carene. The relative importance of aerosol formation from each type of reaction for bicyclic olefin photooxidation is elucidated.
Article
An environmental chamber/Fourier transform infrared system was used to determine the rate coefficient k1 for the gas-phase reaction of OH with 2-methyl-3-buten-2-ol (MBO, (CH3)2C(OH)CH=CH2), relative to the rate of its reaction with ethylene (k2) and propylene (k3). Experiments performed at 295+/-1K, in 700 torr total pressure of air, gave k1=(6.9+/-1.0)×10-11cm3molecule-1s-1. At 295+/-1K, the reaction of OH with MBO yielded, on a per mole basis, (52+/-5)% acetone, (50+/-5)% glycolaldehyde, and (35+/-4)% formaldehyde. The production of acetone from the oxidation of MBO may be of significance globally. The kinetics and mechanism of the reaction of chlorine atoms with MBO (k15) have also been studied at 700 torr total pressure of air and 295+/-1K. The rate coefficient was determined using a relative rate technique, with ethane (k16), ethylene (k17), and cyclohexane (k18) as reference compounds. The value of k15 was found to be (3.3+/-0.4)×10-10cm3molecule-1s-1 at 295 K. The major carbon-containing products obtained in the Cl-atom oxidation of MBO were acetone (47+/-5)%, chloroacetaldehyde (53+/-5)%, HCOCl (
Article
The molecular composition of particle phase ozonolysis products of alpha-pinene is investigated to comprehend the aerosol formation process following the VOC oxidation, focusing on an understanding of new particle formation. Two analytical approaches are applied to identify low-volatile oxidation products in the particle phase; off-line investigations using preconcentration on Tenax TA© followed by solvent extraction and liquid chromatography/mass spectrometry as well as an on-line technique, in which the organic aerosols are introduced directly into the ion source of a mass spectrometer (atmospheric pressure chemical ionization/mass spectrometry (APCI/MS)). Both techniques showed the formation of difunctional carboxylic acids, compounds whose physico-chemical properties will govern most of their mass into the particle phase. Furthermore, stable binary diacid adducts could be identified by MSn-experiments. These observations might give insight into the process of new particle formation by heteromolecular homogeneous nucleation, indicating that the initial cluster formation cannot be described by macroscopic properties of single oxidation products. Instead, strong intermolecular forces between different diacids might play a key role in the formation of initial nuclei and their subsequent growth.
Article
Measurements of peroxyacetyl nitrate (PAN), peroxypropionyl nitrate (PPN), and peroxymethacryloyl nitrate (MPAN) were made during the Southern Oxidants Study 1995 Nashville/Middle Tennessee Ozone Study at the Youth Inc. Ranch southeast of Nashville from June 29 to July 26. These measurements were made along with those of isoprene and its oxidation products methacrolein (MACR) and methyl vinyl ketone (MVK), other carbonyl compounds, and supporting measurements. This data set represents the first high-frequency, simultaneous measurements of MPAN and its precursor, MACR as well as PPN and its precursor propanal. The NOx sensitivity of isoprene chemistry can be studied with data from this site because large and widely fluctuating levels of NOx were experienced as a result of the proximity to the Nashville urban center. Mean mixing ratios of PAN, PPN, MPAN, and MACR were 485, 50, 30, and 290 parts per trillion by volume respectively. The mean diurnal cycle of MPAN closely tracks that of MACR and was found to be considerably sharper than the mean diurnal cycles of PAN, PPN, and O3, showing that MPAN is closely dependent on the availability of MACR. Considerable levels of MPAN and MACR appear to develop at night above a nocturnal boundary layer and are partly responsible for a commonly observed morning increase. Early morning OH reaction with MACR also produces MPAN in the morning. With the high summer temperatures at Youth Inc., the MPAN lifetime is largely determined by thermal decomposition, although OH and O3 chemistry could substantially reduce the ambient lifetime. Additional loss mechanisms for MPAN and dependence on a single source make MPAN more sensitive to photochemical activity and NOx than is PAN. Unless quickly advected to colder, less photochemically active regions of the atmosphere, the contribution of MPAN to O3 formation through long-range transport of NOx is likely to be less significant in comparison with PAN and PPN. Its influence is more limited to local O3 production, so MPAN can be a useful indicator of local-scale, active biogenic photochemistry.
Article
The compound 2-butanol has been used to scavenge >=95% of the OH radicals formed in the reactions of O3 with the alkenes 2,3-dimethyl-2-butene and 2-methyl-2-butene and with the monoterpenes alpha-pinene and sabinene at 296+/-2 K and atmospheric pressure of air, with the OH radical formation yields from these O3 reactions being obtained from the amounts of 2-butanone formed. The rate constant for the reaction of the OH radical with 2-butanol was measured using a relative rate method; the rate constant was determined to be (9.2+/-2.4)×10-12cm3molecule-1s-1 at 296+/-2 K, where the indicated error includes the estimated overall uncertainties in the rate constant for the reference organic (cyclohexane). The formation yield of 2-butanone from the reaction of the OH radical with 2-butanol was determined to be 0.695+/-0.073. Using this 2-butanone formation yield from the OH radical reaction with 2-butanol, the OH radical formation yields from the reactions of O3 with 2,3-dimethyl-2-butene, 2-methyl-2-butene, alpha-pinene, and sabinene were determined to be 0.80+/-0.12, 0.93+/-0.14, 0.76+/-0.11, and 0.33+/-0.06, respectively. These OH radical formation yields agree to within +/-25% with the yields previously derived using cyclohexane to scavenge OH radicals and measuring the amounts of cyclohexanone plus cyclohexanol formed. Our present OH radical formation yield for 2,3-dimethyl-2-butene is also in good agreement with the value of 0.7 previously reported from a comprehensive product study.
Article
The mixing ratios of methyl vinyl ketone (CH[sub 2]=CHCOCH[sub 3]) and methacrolein (CH[sub 2]=C(CH[sub 3])COH) were measured at a site located in the Kinterbish Wildlife Management Area in western Alabama. The measurements were made between June 15 and July 20, 1990. Considering all the data over the whole measurement period, the concentrations of these two carbonyls were approximately equal at this isolated rural site. The average mixing ratios for methyl vinyl ketone and methacrolein were 0.98 parts per billion by volume (ppbv) and 0.66 ppbv, respectively, while the medians were 0.87 ppbv and 0.57 ppbv. The methyl vinyl ketone mixing ratio varied from 3.4 ppbv to the detection limit of the instrument, =0.01 ppbv, while the methacrolein mixing ratio varied from 2.6 ppbv to 0.027 ppbv. These carbonyls constituted a significant fraction of the volatile organic compounds observed at the site: theft mixing ratios, measured 2 m above the top of the forest canopy, were less than that of the dominant compound isoprene but were considerably greater than the mixing ratios of anthropogenic compounds (e.g., benzene). The mixing ratios of methyl vinyl ketone and methacrolein were found to be highly correlated and exhibited a systematic variation with respect to each other. On average, during the day, methyl vinyl ketone was larger than methacrolein, while methacrolein tended to be slightly larger during the night. The systematic behavior of these compounds with respect to each other and other compounds measured at the site were simulated using a one-dimensional photochemical model. These observations were consistent with the production and loss of isoprene, methyl vinyl ketone, and methacrolein by photochemical oxidation reactions. 39 refs., 11 figs., 2 tabs.