A. R. Rickard

University of Leeds, Leeds, England, United Kingdom

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Publications (70)145.71 Total impact

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    ABSTRACT: We present measurements of a long range smoke transport event recorded on 20–21 July 2011 over Halifax, Nova Scotia, Canada, during the Quantifying the impact of BOReal forest fires on Tropospheric oxidants over the Atlantic using Aircraft and Satellites (BORTAS-B) campaign. Ground-based Fourier transform spectrometers and photometers detected air masses associated with large wildland fires burning in eastern Manitoba and western Ontario. We investigate a plume with high trace gas amounts but low amounts of particles that preceded and overlapped at the Halifax site with a second plume with high trace gas loadings and significant amounts of particulate material. We show that the first plume experienced a meteorological scavenging event but the second plume had not been similarly scavenged. This points to the necessity to account carefully for the plume history when considering long range transport since simultaneous or near-simultaneous times of arrival are not necessarily indicative of either similar trajectories or meteorological history. We investigate the origin of the scavenged plume, and the possibility of an aerosol wet deposition event occurring in the plume ~24 h prior to the measurements over Halifax. The region of lofting and scavenging is only monitored on an intermittent basis by the present observing network, and thus we must consider many different pieces of evidence in an effort to understand the early dynamics of the plume. Through this discussion we also demonstrate the value of having many simultaneous remote-sensing measurements in order to understand the physical and chemical behaviour of biomass burning plumes.
    Atmospheric Chemistry and Physics Discussions. 02/2014; 14:3395-3426.
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    ABSTRACT: Reaction with the hydroxyl radical (OH) is the dominant removal mechanism for virtually all volatile organic compounds (VOCs) in the atmosphere, however it can be difficult to reconcile measured OH reactivity with known sinks. Unresolved higher molecular weight VOCs contribute to OH sinks, of which monoaromatics are potentially an important sub-class. A method based on comprehensive two-dimensional gas chromatography coupled to time of flight mass spectrometry (GC × GC-TOFMS) has been developed that extends the degree with which larger VOCs can be individually speciated from whole air samples (WAS). The technique showed excellent sensitivity, resolution and good agreement with an established GC-FID method, for compounds amenable to analysis on both instruments. Measurements have been made of VOCs within the UK east coast marine boundary layer and free troposphere, using samples collected from five aircraft flights in winter 2011. Ten monoaromatic compounds with an array of different alkyl ring substituents have been quantified, in addition to the simple aromatics, benzene, toluene, ethyl benzene and σm- and p-xylene. These additional compounds were then included into constrained box model simulations of atmospheric chemistry occurring at two UK rural and suburban field sites in order to assess the potential impact of these larger monoaromatics species on OH reactivity; they have been calculated to contribute an additional 2-6% to the overall modelled OH loss rate, providing a~maximum additional OH sink of ~0.9 s-1.
    Atmospheric Chemistry and Physics 12/2013; 13(12):32423-32457. · 4.88 Impact Factor
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    ABSTRACT: The gas-phase reaction of ozone with unsaturated VOCs, alkenes, is an important source of the critical atmospheric oxidant OH, especially at night when other photolytic radical initiation routes cannot occur. Alkene ozonolysis is also known to directly form HO2 radicals, which may be readily converted to OH through reaction with NO, but whose formation is poorly understood. We report a study of the radical (OH, HO2 and RO2) production from a series of small alkenes (propene, 1-butene, cis-2-butene, trans-2-butene, 2-methylpropene, 2,3-dimethyl-2-butene (tetramethyl ethene, TME) and isoprene). Experiments were performed in the European Photoreactor (EUPHORE) atmospheric simulation chamber, with OH and HO2 levels directly measured by laser-induced fluorescence (LIF), and HO2 +  RO2 levels measured by peroxy-radical chemical amplification (PERCA). OH yields were found to be in good agreement with the majority of previous studies performed under comparable conditions (atmospheric pressure, long timescales) using tracer and scavenger approaches. HO2 yields ranged from 4 % (trans-2-butene) to 34 % (2-methylpropene), lower than previous experimental determinations. Increasing humidity further reduced the HO2 yields obtained, by typically 50 % for an RH increase from 0.5 to 30 %, suggesting that HOx production from alkene ozonolysis may be lower than current models suggest under (humid) ambient atmospheric boundary layer conditions. The mechanistic origin of the OH and HO2 production observed is discussed in the context of previous experimental and theoretical studies.
    The Journal of Physical Chemistry A 10/2013; · 2.77 Impact Factor
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    ABSTRACT: We present an analysis of ozone (O3) photochemistry observed by aircraft measurements of boreal biomass burning plumes over eastern Canada in the summer of 2011. Measurements of O3 and a number of key chemical species associated with O3 photochemistry, including non-methane hydrocarbons (NMHCs), nitrogen oxides (NOx) and total nitrogen containing species (NOy), were made from the UK FAAM BAe-146 research aircraft as part of the "quantifying the impact of BOReal forest fires on Tropospheric oxidants over the Atlantic using Aircraft and Satellites" (BORTAS) experiment between 12 July and 3 August 2011. The location and timing of the aircraft measurements put BORTAS into a unique position to sample biomass burning plumes from the same source region in Northwestern Ontario with a range of ages. We found that O3 mixing ratios measured in biomass burning plumes were indistinguishable from non-plume measurements, but evaluating them in relationship to measurements of carbon monoxide (CO), total alkyl nitrates (ΣAN) and the surrogate species NOz (= NOy-NOx) revealed that the potential for O3 production increased with plume age. We used NMHC ratios to estimate photochemical ages of the observed biomass burning plumes between 0 and 10 days. The BORTAS measurements provided a wide dynamic range of O3 production in the sampled biomass burning plumes with ΔO3/ΔCO enhancement ratios increasing from 0.020 ± 0.008 ppbv ppbv−1 in plumes with photochemical ages less than 2 days to 0.55 ± 0.29 ppbv ppbv−1 in plumes with photochemical ages greater than 5 days. We found that the main contributing factor to the variability in the ΔO3/ΔCO enhancement ratio was ΔCO in plumes with photochemical ages less than 4 days, and that was a transition to ΔO3 becoming the main contributing factor in plumes with ages greater than 4 days. In comparing O3 mixing ratios with components of the NOy budget, we observed that plumes with ages between 2 and 4 days were characterised by high aerosol loading, relative humidity greater than 40%, and low ozone production efficiency (OPE) of 7.7 ± 3.5 ppbv ppbv−1 relative to ΣAN and 1.6 ± 0.9 ppbv ppbv−1 relative to NOz. In plumes with ages greater than 4 days, OPE increased to 472 ± 28 ppbv ppbv−1 relative to ΣAN and 155 ± 5 ppbv ppbv−1 relative to NOz. From the BORTAS measurements we estimated that aged plumes with low aerosol loading were close to being in photostationary steady state and O3 production in younger plumes was inhibited by high aerosol loading and greater production of ΣAN relative to O3. The BORTAS measurements of O3 photochemistry in boreal biomass burning plumes were found to be consistent with previous summertime aircraft measurements made over the same region during the Arctic Research of the Composition of the Troposphere (ARCTAS-B) in 2008 and Atmospheric Boundary Layer Experiment (ABLE 3B) in 1990.
    Atmospheric Chemistry and Physics. 08/2013; 13:7321–7341.
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    ABSTRACT: We describe the design and execution of the BORTAS (Quantifying the impact of BOReal forest fires on Tropospheric oxidants using Aircraft and Satellites) experiment, which has the overarching objective of understanding the chemical aging of airmasses that contain the emission products from seasonal boreal wildfires and how these airmasses subsequently impact downwind atmospheric composition. The central focus of the experiment was a two-week deployment of the UK BAe-146-301 Atmospheric Research Aircraft (ARA) over eastern Canada. The planned July 2010 deployment of the ARA was postponed by 12 months because of activities related to the dispersal of material emitted by the Eyjafjallajo¨kull volcano. However, most other planned model and measurement activities, including ground-based measurements at the Dalhousie University Ground Station (DGS), enhanced ozonesonde launches, and measurements at the Pico Atmospheric Observatory in the Azores, went ahead and constituted phase A of the experiment. Phase B of BORTAS in July 2011 included the same measurements, but included the ARA, special satellite observations and a more comprehensive measurement suite at the DGS. The high-frequency aircraft data provided a comprehensive snapshot of the pyrogenic plumes from wildfires. The coordinated ground-based and sonde data provided detailed but spatially-limited information that put the aircraft data into context of the longer burning season. We coordinated aircraft vertical profiles and overpasses of the NASA Tropospheric Emission Spectrometer and the Canadian Atmospheric Chemistry Experiment. These space-borne data, while less precise than other data, helped to relate the two-week measurement campaign to larger geographical and longer temporal scales. We interpret these data using a range of chemistry models: from a near-explicit gas-phase chemical mechanism, which tests out under standing of the underlying chemical mechanism, to regional and global 3-D models of atmospheric transport and lumped chemistry, which helps to assess the performance of the simplified chemical mechanism and effectively act as intermediaries between different measurement types. We also present an overview of some of the new science that has originated from this project from the mission planning and execution to the analysis of the ground-based, aircraft, and space-borne data.
    ATMOSPHERIC CHEMISTRY AND PHYSICS 07/2013; 13:6239-6261. · 5.51 Impact Factor
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    ABSTRACT: We present an analysis of ozone photochemistry observed in boreal biomass burning plumes over eastern Canada in the summer of 2011. Measurements of ozone and a number of key chemical species associated with ozone pho-tochemistry, including non-methane hydrocarbons (NMHCs), nitrogen oxides (NO x) and total nitrogen containing species (NO y), were made from the UK FAAM BAe-146 research aircraft as part of the quantifying the impact of BOReal forest fires on Tropospheric oxidants over the Atlantic using Aircraft and Satellites (BORTAS) experi-ment between 12 July and 3 August 2011. We show that ozone mixing ratios measured in biomass burning plumes were indistinguishable from non-plume measurements, but comparison against measurements of carbon monoxide (CO), total alkyl nitrates (ΣAN) and a surrogate species for photo-oxidation of NO x (NO z = NO y − NO x) revealed that the potential for ozone production increased with plume age. We calculated photochemical ages, from NMHC ratios, for the plumes sampled during BORTAS to range from 0 to 15 days. Ozone production, calculated from ∆O 3 /∆CO enhancement ratios, increased from 0.020 ± 0.008 ppbv ppbv −1 in plumes with photochemical ages less than 2 days to 0.55 ± 0.29 ppbv ppbv −1 in plumes with photochemical ages greater than 5 days. In comparing ozone mixing ratios with components of the NO y budget we show that plumes with ages between 2 and 4 days were characterised by high aerosol loading, relative humidity greater than 40%, and low ozone production efficiencies of 8 ppbv ppbv −1 relative to ΣAN and 2 ppbv ppbv −1 relative to NO z . In plumes with ages greater than 4 days, ozone production efficiency was increased to 473 ppbv ppbv −1 relative to ΣAN and 155 ppbv ppbv −1 relative to NO z . We present the observed plume ozone photochemistry in relation to other geophysical parameters measured from the aircraft and previous measurement campaigns that sampled boreal biomass burning plumes over the same region.
    European Geosciences Union General Assembly 2013; 04/2013
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    ABSTRACT: We use the GEOS-Chem chemistry transport model to quantify the impact of boreal biomass burning on tropospheric oxidant chemistry over the North Atlantic region during summer of 2011. The GEOS-Chem model is used at a spatial resolution of 1/2 degree latitude by 2/3 degree longitude for a domain covering eastern North America, the North Atlantic Ocean and western Europe. We initialise the model with biomass burning emissions from the Fire Locating and Monitoring of Burning Emissions (FLAMBE) inventory and use a modified chemical mechanism providing a detailed description of ozone photochemistry in boreal biomass burning outflow derived from the Master Chemical Mechanism (MCM). We evaluate the 3-D model distribution of ozone and tracers associated with biomass burning against measurements made by the UK FAAM BAe-146 research aircraft, ozonesondes, ground-based and satellite instruments as part of the BORTAS experiment between 12 July and 3 August 2011. We also use the GEOS-Chem model adjoint to fit the model to BORTAS measurements to anal-yse the sensitivity of the model chemical mechanism and ozone distribution to wildfire emissions in central Canada.
    European Geosciences Union General Assembly 2013; 04/2013
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    ABSTRACT: The oxidation of volatile organic compounds (VOCs) leads to formation of ozone and SOA, with consequences for air quality, health, crop yields, atmospheric chemistry and radiative transfer. Recent observations have identified Methyl Chavicol ("MC": Estragole; 1-allyl-4-methoxybenzene, C10H12O) as a major BVOC above pine forests in the USA, and oil palm plantations in Malaysian Borneo. Palm oil cultivation, and hence MC emissions, may be expected to increase with societal food and bio fuel demand. We present the results of a series of simulation chamber experiments to assess the atmospheric fate of MC. Experiments were performed in the EUPHORE facility, monitoring stable product species, radical intermediates, and aerosol production and composition. We determine rate constants for reaction of MC with OH and O3, and ozonolysis radical yields. Stable product measurements (FTIR, PTRMS, GC-SPME) are used to determine the yields of stable products formed from OH- and O3- initiated oxidation, and to develop an understanding of the initial stages of the MC degradation chemistry. A surrogate mechanism approach is used to simulate MC degradation within the MCM, evaluated in terms of ozone production measured in the chamber experiments, and applied to quantify the role of MC in the real atmosphere.
    04/2013;
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    ABSTRACT: We describe the design and execution of the BORTAS (Quantifying the impact of BOReal forest fires on Tropospheric oxidants using Aircraft and Satellites) experiment, which has the overarching objective of understanding the chemical aging of airmasses, containing the emission products from seasonal boreal wildfires, and how they impact downwind atmospheric composition. The central focus of the experiment was a two-week deployment of the UK BAe-146-301 Atmospheric Research Aircraft (ARA) over eastern Canada. This was complemented by ground-based measurements at the Dalhousie University Ground Station (DGS) and the University of Toronto, enhanced ozonesonde launches, measurements on the Pico Mountain Atmospheric Observatory in the Azores, and coordinated space-borne measurements. Integration of these data has helped us to describe pollution plumes from wildfires on a wide spectrum of temporal and spatial scales. These data are interpreted using a range of chemistry models, from a near-explicit gas-phase chemical mechanism to a regional and global model of atmospheric transport and lumped chemistry, and data assimilation tools. We also provide a brief science overview of the project, providing the platform for co-submitted science abstracts.
    04/2013;
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    ABSTRACT: The formation of HCO and of H in the photolysis of glyoxal have been investigated over the wavelength ranges 310-335 nm for HCO and 193-340 nm for H. Dye laser photolysis was coupled with cavity ring-down spectroscopy for HCO, and with laser induced fluorescence spectroscopy for H. Absolute quantum yields were determined using actinometers based on (a) Cl(2) photolysis and the Cl + HCHO reaction for HCO and (b) N(2)O photolysis (and O(1)D + H(2)) and CH(2)CO photolysis (and CH(2) + O(2)) for H. The quantum yields were found to be pressure independent in this wavelength region. Quantum yields for all product channels under atmospheric conditions were calculated and compared with literature values. Differences between this work and previously published work and their atmospheric implications are discussed.
    Physical Chemistry Chemical Physics 02/2013; · 3.83 Impact Factor
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    ABSTRACT: We present an analysis of ozone photochemistry observed by aircraft measurements of boreal biomass burning plumes over Eastern Canada in the summer of 2011. Measurements of ozone and a number of key chemical species associated with ozone photochemistry, including non-methane hydrocarbons (NMHCs), nitrogen oxides (NOx) and total nitrogen containing species (NOy), were made from the UK FAAM BAe-146 research aircraft as part of the quantifying the impact of BOReal forest fires on tropospheric oxidants over the Atlantic using Aircraft and Satellites (BORTAS) experiment between 12 July and 3 August 2011. We found that ozone mixing ratios measured in biomass burning plumes were indistinguishable from non-plume measurements, but evaluating them in relationship to measurements of carbon monoxide (CO), total alkyl nitrates (ΣAN) and the surrogate species NOz (=NOy - NOx) revealed that the potential for ozone production increased with plume age. We used NMHC ratios to estimate photochemical ages of the observed biomass burning plumes between 0 and 15 days. Ozone production, calculated from ΔO3/ΔCO enhancement ratios, increased from 0.020 ± 0.008 ppbv ppbv-1 in plumes with photochemical ages less than 2 days to 0.55 ± 0.29 ppbv ppbv-1 in plumes with photochemical ages greater than 5 days. In comparing ozone mixing ratios with components of the NOy budget we observed that plumes with ages between 2 and 4 days were characterised by high aerosol loading, relative humidity greater than 40%, and low ozone production efficiencies of 8 ppbv ppbv-1 relative to ΣAN and 2 ppbv ppbv-1 relative to NOz. In plumes with ages greater than 4 days, ozone production efficiency increased to 473 ppbv ppbv-1 relative to ΣAN and 155 ppbv ppbv-1 relative to NOz. From the BORTAS measurements we estimated that aged plumes with low aerosol loading were close to being in photostationary steady state and ozone production in younger plumes was inhibited by high aerosol loading and greater production of ΣAN relative to ozone. The BORTAS measurements of ozone photochemistry in boreal biomass burning plumes were found to be consistent with previous summertime aircraft measurements made over the same region during the Arctic Research of the Composition of the troposphere (ARCTAS-B) in 2008 and Atmospheric Boundary Layer Experiment (ABLE 3B) in 1990.
    Atmospheric Chemistry and Physics 01/2013; 13(1):1795-1853. · 4.88 Impact Factor
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    ABSTRACT: Recent laboratory and modelling studies have shown that reactive uptake of low molecular weight alpha-dicarbonyls such as glyoxal (GLY) by aerosols is a potentially significant source of secondary organic aerosol (SOA). However, previous studies disagree in the magnitude of the uptake of GLY, the mechanism involved and the physicochemical factors affecting particle formation. In this study, the chemistry of GLY with ammonium sulfate (AS) in both bulk laboratory solutions and in aerosol particles is investigated. For the first time, Aerosol Time of Flight Mass Spectrometry (ATOFMS), a single particle technique, is used together with offline (ESI-MS and LC-MS2) mass spectrometric techniques to investigate the change in composition of bulk solutions of GLY and AS resulting from aqueous photooxidation by OH and from ageing of the solutions in the dark. The mass spectral ions obtained in these laboratory studies were used as tracers of GLY uptake and chemistry in AS seed particles in a series of experiments carried out under dark and natural irradiated conditions at the outdoor European Photo-reactor (EUPHORE). Glyoxal oligomers formed were not detected by the ATOFMS, perhaps due to inefficient absorption at the laser wavelength. However, the presence of organic nitrogen compounds, formed by reaction of GLY with ammonia was confirmed, resulting in an increase in the absorption efficiency of the aerosol, and this increased the number of particles successfully ionised by the ATOFMS. A number of light absorbing organic nitrogen species, including 1H-imidazole, 1H-imidazole-2-carboxaldehyde, 2,2'-bis-imidazole and a glyoxal substituted 2,2'-bisimidazole, previously identified in aqueous laboratory solutions, were also identified in chamber aerosol and formed on atmospherically relevant timescales. An additional compound, predicted to be 1,2,5-oxadiazole, had an enhanced formation rate when the chamber was open and is predicted to be formed via a light activated pathway involving radical oxidation of ammonia to hydroxylamine, followed by subsequent reaction with glyoxal to form an intermediate glyoxime.
    Faraday Discussions 01/2013; 165:447-72. · 3.82 Impact Factor
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    ABSTRACT: Forests fires are a significant source of chemicals to the atmosphere including numerous non-methane organic compounds (NMOCs). We report airborne measurement of hydrocarbons, acetone and methanol from >500 whole air samples collected over Eastern Canada, including interceptions of several different boreal biomass burning plumes. From these and concurrent measurements of carbon monoxide (CO) we derive fire emission ratios for 29 different organic species relative to the emission of CO. These range from 8.9 ± 3.2 ppt ppb-1 CO for methanol to 0.007 ± 0.004 ppt ppb-1 CO for cyclopentane. The ratios are in good to excellent agreement with literature values. Using the GEOS-Chem global 3-D chemical transport model (CTM) we show the influence of biomass burning on the global distributions of benzene, toluene, ethene and propene (species which are controlled for air quality purposes and sometimes used as indicative tracers of anthropogenic activity). Using our observationally derived emission ratios and the GEOS-Chem CTM, we show that biomass burning can be the largest fractional contributor to observed benzene, toluene, ethene and propene levels in many global locations. The widespread biomass burning contribution to atmospheric benzene, a heavily regulated air pollutant, suggests that pragmatic approaches are needed when setting air quality targets as tailpipe and solvent emissions decline in developed countries. We subsequently determine the extent to which the 28 global-status World Meteorological Organisation - Global Atmosphere Watch stations worldwide are influenced by biomass burning sourced benzene, toluene, ethene and propene as compared to their exposure to anthropogenic emissions.
    ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2013; 13(2):851-867. · 5.51 Impact Factor
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    ABSTRACT: Boreal forest fires are a significant source of chemicals to the atmosphere including numerous non-methane hydrocarbons (NMHCs). We report airborne measurements of NMHCs, acetone and methanol from > 500 whole air samples collected over Eastern Canada, including interception of several different boreal biomass burning plumes. From these and concurrent measurements of carbon monoxide (CO) we derive fire emission ratios for 29 different species relative to the emission of CO. These range from 8.9 ± 3.2 ppt ppb-1 CO for methanol to 0.007 ± 0.004 ppt ppb-1 CO for cyclopentane. The ratios are in good to excellent agreement with recent literature values. Using the GEOS-Chem global 3-D chemical transport model (CTM) we show the influence of biomass burning on the global distributions of benzene, toluene, ethene and propene (species considered generally as indicative tracers of anthropogenic activity). Using our derived emission ratios and the GEOS-Chem CTM, we show that biomass burning can be the largest fractional contributor to observed benzene, toluene, ethene and propene in many global locations. The widespread biomass burning contribution to atmospheric benzene, a heavily regulated air pollutant, suggests that pragmatic approaches are needed when setting air quality targets as tailpipe and solvent emissions continue to decline. We subsequently determine the extent to which the 28 Global WMO-GAW stations worldwide are influenced by biomass burning sourced benzene, toluene, ethene and propene when compared to their exposure to anthropogenic emissions.
    Atmospheric Chemistry and Physics 09/2012; 12(9):23433-23469. · 4.88 Impact Factor
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    ABSTRACT: During July 2011 the UK BAe-146 research aircraft was based at Halifax NS to make detailed in situ chemical composition measurements of boreal biomass burning plumes as part of the UK-Canadian BORTAS project (http://www.geos.ed.ac.uk/research/eochem/bortas/). The primary objective of BORTAS is to quantify the impact of boreal biomass burning on tropospheric oxidant chemistry over the North Atlantic. The aircraft measurements were supported by ozonesondes launched from five locations across eastern Canada, with support from Environment Canada, and by LIDAR and other ground-based measurements at Dalhousie University. Boreal biomass burning plumes, principally from forest fires in NW Ontario and North West Territories, were intercepted and sampled on the majority of the 15 research flights made during the campaign. Plumes were identified by elevated mixing ratios of carbon monoxide, acetonitrile, and black carbon. We estimate photochemical ages of these plumes using ratios of hydrocarbons, inferred from whole air canister measurements taken on the aircraft. Plume ages range from 0 to 10 days when they are intercepted over eastern Canada between the forest fires in NW Ontario and the maritime provinces. Simple measures of net ozone production (e.g., enhancement ratios of ozone and carbon monoxide) increase as a function of photochemical age, consistent with some previous measurement campaigns over Canada and Siberia. We present a detailed analysis of the BORTAS aircraft and ozonesonde measurements to quantify the factors influencing the observed ozone photochemistry and to distinguish the biomass burning air masses from anthropogenic precursor emissions and ozone transport from the stratosphere.
    Quadrenniel Ozone Symposium, Toronto, Canada; 08/2012
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    ABSTRACT: A degradation mechanism for β-caryophyllene has recently been released as part of version 3.2 of the Master Chemical Mechanism (MCM v3.2), describing the gas phase oxidation initiated by reaction with ozone, OH radicals and NO3 radicals. A detailed overview of the construction methodology is given, within the context of reported experimental and theoretical mechanistic appraisals. The performance of the mechanism has been evaluated in chamber simulations in which the gas phase chemistry was coupled to a representation of the gas-to-aerosol partitioning of 280 multi-functional oxidation products. This evaluation exercise considered data from a number of chamber studies of either the ozonolysis of β-caryophyllene, or the photo-oxidation of β-caryophyllene/NOx mixtures, in which detailed product distributions have been reported. This includes the results of a series of photo-oxidation experiments performed in the University of Manchester aerosol chamber, also reported here, in which a comprehensive characterization of the temporal evolution of the organic product distribution in the gas phase was carried out, using Chemical Ionisation Reaction Time-of-Flight Mass Spectrometry (CIR-TOF-MS), in conjunction with measurements of NOx, O3 and SOA mass loading. The CIR-TOF-MS measurements allowed approximately 45 time-resolved product ion signals to be detected, which were assigned on the basis of the simulated temporal profiles of the more abundant MCM v3.2 species, and their probable fragmentation patterns. The evaluation studies demonstrate that the MCM v3.2 mechanism provides an acceptable description of β-caryophyllene degradation under the chamber conditions considered, with the temporal evolution of the observables identified above generally being recreated within the uncertainty bounds of key parameters within the mechanism. The studies have highlighted a number of areas of uncertainty or discrepancy, where further investigation would be valuable to help interpret the results of chamber studies and improve detailed mechanistic understanding. These particularly include: (i) quantification of the yield and stability of the secondary ozonide (denoted BCSOZ in MCM v3.2), formed from β-caryophyllene ozonolysis, and elucidation of the details of its further oxidation, including whether the products retain the "ozonide" functionality; (ii) investigation of the impact of NOx on the β-caryophyllene ozonolysis mechanism, in particular its effect on the formation of β-caryophyllinic acid (denoted C137CO2H in MCM v3.2), and elucidation of its formation mechanism; (iii) routine independent identification of β-caryophyllinic acid, and its potentially significant isomer β-nocaryophyllonic acid (denoted C131CO2H in MCM v3.2); (iv) more precise quantification of the primary yield of OH (and other radicals) from β-caryophyllene ozonolysis; (v) quantification of the yields of the first-generation hydroxy nitrates (denoted BCANO3, BCBNO3 and BCCNO3 in MCM v3.2) from the OH-initiated chemistry in the presence of NOx; and (vi) further studies in general to improve the identification and quantification of products formed from both ozonolysis and photo-oxidation, including confirmation of the simulated formation of multifunctional species containing hydroperoxide groups, and their important contribution to SOA under NOx-free conditions.
    ATMOSPHERIC CHEMISTRY AND PHYSICS 06/2012; 12(11):5275-5308. · 5.51 Impact Factor
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    ABSTRACT: The α-dicarbonyl compounds glyoxal (GLY, CH(O)CHO) and methylglyoxal (MGLY, CH3C(O)CHO)) are ubiquitous intermediates formed in the photooxidation of a wide range of anthropogenic and biogenic volatile organic compounds (VOCs). Recent measurements demonstrate that large uncertainties exist in the amount of glyoxal formed from isoprene photooxidation, the dominant VOC emitted into the atmosphere (1, 2). In addition, α-dicarbonyls are known to be precursors of secondary organic aerosol (SOA) and can potentially form a significant fraction of the missing global SOA in atmospheric models (3, 4). However, the exact role of such compounds is still not well established. One of the main reasons for such uncertainties is the difficulty in measuring them, as they are very reactive and difficult to handle experimentally. In order to elucidate both the chemical and instrumental issues related to the quantitative measurement of these compounds, a short experimental chamber campaign was carried out in the EUPHORE photo-reactor in Valencia, Spain to compare a number of currently available techniques (both optical and spectrometric). The campaign comprised a set of experiments simulating typical urban and semi-rural conditions. Measurements were performed over a range of concentrations in order to investigate the impacts of the presence of potential interferants in the gas mixtures sampled from the chamber (i.e. aerosol, NOx, short chain carbonyls and ozone). The gas and aerosol phase compositional evolution was monitored simultaneously. Different amounts of GLY and/or MGLY were added directly to the chamber or were generated in-situ from the oxidation of various VOC precursors. The following instrumental techniques were employed during the campaign: (Blue) LED-CE-DOAS (cavity enhanced differential optical absorption spectroscopy), long-path DOAS, SPME (solid phase micro extraction) -GC/MS, Fourier Transform Infrared (FTIR) spectroscopy, GC-ECD (electron capture detection), BBCEAS (broadband cavity enhanced absorption spectroscopy), LIP (Laser induced phosphorescence), CIR-TOF-MS (chemical ionization time-of-flight mass spectrometry), ATOFMS (aerosol time-of-flight mass spectrometry), FTICR (Fourier transform ion cyclotron resonance mass spectrometry, and LC-MSn (liquid chromatography-ion trap mass spectrometry). Experiments were separated in two groups; blind experiments where the participants share their data only with the referee and open experiments where data was shared between all participants during the execution of the experiments. We will present an overview of the campaign in terms of participants, instruments, definition of experiments as well as selected results. More information on the campaign can be found on the following website: http://euphore.es/aldiint/aldiint.html.
    04/2012;
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    ABSTRACT: A degradation mechanism for β-caryophyllene has recently been released as part of version 3.2 of the Master Chemical Mechanism (MCM v3.2), describing the gas phase oxidation initiated by reaction with ozone, OH radicals and NO3 radicals. A detailed overview of the construction methodology is given, within the context of reported experimental and theoretical mechanistic appraisals. The performance of the mechanism has been evaluated in chamber simulations in which the gas phase chemistry was coupled to a representation of the gas-to-aerosol partitioning of 280 multi-functional oxidation products. This evaluation exercise considered data from a number of chamber studies of either the ozonolysis of β-caryophyllene, or the photo-oxidation of β-caryophyllene/NOx mixtures, in which detailed product distributions have been reported. This includes the results of a series of photo-oxidation experiments performed in the University of Manchester aerosol chamber, also reported here, in which a comprehensive characterization of the temporal evolution of the organic product distribution in the gas phase was carried out, using Chemical Ionisation Reaction Time-of-Flight Mass Spectrometry (CIR-TOF-MS), in conjunction with measurements of NOx, O3 and SOA mass loading. The CIR-TOF-MS measurements allowed approximately 45 time-resolved product ion signals to be detected, which were assigned on the basis of the simulated temporal profiles of the more abundant MCM v3.2 species, and their probable fragmentation patterns. The evaluation studies demonstrate that the MCM v3.2 mechanism provides a generally acceptable description of β-caryophyllene degradation, under the chamber conditions considered, and a reliable basis for simulations where a representation of chemical detail is required. The studies have also highlighted a number of areas of uncertainty, where further investigation would be valuable to help interpret the results of chamber studies and improve detailed mechanistic understanding. These particularly include: (i) quantification of the yield and stability of the secondary ozonide (denoted BCSOZ in MCM v3.2), formed from β-caryophyllene ozonolysis, and elucidation of the details of its further oxidation, including whether the products retain the "ozonide" functionality; (ii) investigation of the impact of NOx on the β-caryophyllene ozonolysis mechanism, in particular its effect on the formation of β-caryophyllinic acid (denoted C137CO2H in MCM v3.2), and elucidation of its formation mechanism; (iii) routine independent identification of β-caryophyllinic acid, and its potentially significant isomer β-nocaryophyllonic acid (denoted C131CO2H in MCM v3.2); (iv) more precise quantification of the primary yield of OH (and other radicals) from β-caryophyllene ozonolysis; (v) quantification of the yields of the first-generation hydroxy nitrates (denoted BCANO3, BCBNO3 and BCCNO3 in MCM v3.2) from the OH-initiated chemistry in the presence of NOx; and (vi) further studies in general to improve the identification and quantification of products formed from both ozonolysis and photo-oxidation, including confirmation of the simulated formation of multifunctional species containing hydroperoxide groups, and their important contribution to SOA under NOx-free conditions.
    Atmospheric Chemistry and Physics 01/2012; 12(1):2891-2974. · 4.88 Impact Factor
  • [show abstract] [hide abstract]
    ABSTRACT: Ozone is one of the most important trace gases in the troposphere being on the one hand an integral element in the control of the oxidizing capacity of the troposphere and on the other hand a climate gas. Although there is still a debate on the relative contribution from photochemistry and stratospheric intrusions to the origin of tropospheric ozone, the current consensus view is that photochemistry is the major contributor to the observed ozone levels [1, 2]. The ozone in the troposphere displays a clear seasonal cycle, which depends on a multitude of factors, such as the proximity to large source areas of ozone precursors, the geographical location and meteorological factors. In certain locations such as in the free troposphere or unpolluted sites in the Northern hemisphere tropospheric ozone shows a spring maximum but there has been much debate as to the origins of this phenomenon mainly due to the problems rising from the interpretation of measurements and the interactions of processes occurring on differing scales from the local to the global scale [3]. Several chemical theories were developed to explain the observed spring ozone maximum in the free troposphere of the Northern midlatitudes [4, 5].
    07/2011: pages 365-372;

Publication Stats

457 Citations
145.71 Total Impact Points

Institutions

  • 2006–2014
    • University of Leeds
      • School of Chemistry
      Leeds, England, United Kingdom
  • 2012
    • The University of York
      • Department of Chemistry
      York, England, United Kingdom
  • 2011
    • University of Birmingham
      • School of Geography, Earth and Environmental Sciences
      Birmingham, ENG, United Kingdom
  • 2002–2011
    • University of Leicester
      • Department of Chemistry
      Leicester, ENG, United Kingdom
  • 1998
    • University of Reading
      • Department of Chemistry
      Reading, England, United Kingdom