A. Turnipseed

National Center for Atmospheric Research, Boulder, Colorado, United States

Are you A. Turnipseed?

Claim your profile

Publications (94)260.56 Total impact

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Formation and growth of ultrafine particles is crudely represented in chemistry-climate models, which contributes to uncertainties in aerosol composition, size distribution, and aerosol effects on cloud condensation nuclei (CCN) concentrations. Measurements of ultrafine particles, their precursor gases, and meteorological parameters were performed in a ponderosa pine forest in the Colorado Front Range in July-August 2011, and were analyzed to study processes leading to Aitken-mode Particle burst Events (APEs). These measurements suggest that APEs were associated with the arrival at the site of anthropogenic pollution plumes around noon or in the early afternoon. Number concentrations of ultrafine (4 to 30 nm diameter) particles typically exceeded 10 000 cm-3 during APEs, and these elevated concentrations coincided with increased SO2 and monoterpene concentrations, and led to a factor of two increase in CCN concentrations at 0.5% supersaturation. The APEs were simulated using the regional WRF-Chem model, which was extended to account for ultrafine particle sizes starting at 1 nm in diameter, to include an empirical activation nucleation scheme in the planetary boundary layer, and to explicitly simulate the subsequent growth of Aitken particles by condensation of organic and inorganic vapors. Comparisons with aerosol size distribution measurements showed that simulations using the activation nucleation parameterization reasonably captured aerosol number concentrations and size distribution during APEs, as well as ground level CCN concentrations. Results suggest that sulfuric acid from anthropogenic SO2 triggers APEs, and that the condensation of monoterpene oxidation products onto freshly nucleated particles drives their growth. The simulated growth rate of 3.4 nm h-1 for small particles (4-30 nm in diameter) was comparable to the measured average value of 2.3 nm h-1. Model results also suggest that the presence of APEs tends to modify the composition of sub-100 nm diameter particles, leading to generally higher absolute mass concentrations of sulfate as well as organic aerosols with a higher sulfate content. Sensitivity simulations suggest that the representation of nucleation processes in the model largely influences the predicted number concentrations and thus CCN concentrations. We estimate that nucleation contributes to 65% of surface CCN at 0.5% supersaturation in this pine forest environment.
    ATMOSPHERIC CHEMISTRY AND PHYSICS 10/2014; 14:11011-11029. · 5.51 Impact Factor
  • Thomas Karl, Lisa Kaser, Andrew Turnipseed
    [Show abstract] [Hide abstract]
    ABSTRACT: Isoprene and 2-methyl-3-buten-2-ol (232-MBO) are the dominant biogenic VOCs released throughout the US, thus requiring simultaneous measurements. Recent measurements suggest the presence of isoprene in 232-MBO dominated ecosystems, however analytical difficulties make it problematic to detect both species independently. Based on a new chemical ionization scheme we use eddy covariance measurements to selectively measure fluxes of both species without analytical interference at the Manitou Experimental Forest (MEF) in Colorado. Our measurements show a concentration ratio between isoprene and 232 MBO of 0.24 (ppbv/ppbv), and a flux ratio of 0.10 ([ppbv m/s]/[ppbv m/s]). Daytime average emission factors of isoprene and 232 MBO were 1.4 ± 0.3 and 16.0 ± 3.0 mg/m2/h respectively. Both compounds exhibit light and temperature dependent fluxes. These findings suggest that isoprene is both locally produced and transported to the measurement site dominated by ponderosa pine. This makes it difficult to use MVK and MAC as tracers for estimating the photochemical age of isoprene chemistry at this site. Further our measurements suggest that isoprene can contribute to about 15% of the OH reactivity relative to 232 MBO.
    International Journal of Mass Spectrometry 05/2014; · 2.14 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Total OH reactivity was measured during the Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics and Nitrogen-Southern Rocky Mountain 2008 field campaign (BEACHON-SRM08) held at Manitou Experimental Forest (MEF) in Colorado USA in August, 2008. The averaged total OH reactivity was 6.7 s−1, smaller than that measured in urban (33.4 s−1, Yoshino et al., 2012) and suburban (27.7 s−1, Yoshino et al., 2006) areas in Tokyo in the same season, while sporadically high OH reactivity was also observed during some evenings. The total OH reactivity measurements were accompanied by observations of traces species such as CO, NO, NOy, O3 and SO2 and Volatile Organic Compounds (VOCs). From the calculation of OH reactivity based on the analysis of these trace species, 46.3% of OH reactivity for VOCs came from biogenic species that are dominated by 2-methyl-3-buten-2-ol (MBO), and monoterpenes. MBO was the most prominent contribution to OH reactivity of all trace species. A comparison of observed and calculated OH reactivity shows that the calculated OH reactivity is 29.5% less than the observed value, implying the existence of missing OH sinks. One of the candidates of missing OH is thought to be the oxidation products of biogenic species.
    Atmospheric Environment 03/2014; 85:1–8. · 3.11 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: To survey landscape-scale fluxes of biogenic gases, a 100 m Teflon tube was attached to a tethered balloon as a sampling inlet for a fast response Proton Transfer Reaction Mass Spectrometer (PTRMS). Along with meteorological instruments deployed on the tethered balloon and at 3 m and outputs from a regional weather model, these observations were used to estimate landscape scale biogenic volatile organic compound fluxes with two micrometeorological techniques: mixed layer variance and surface layer gradients. This highly mobile sampling system was deployed at four field sites near Barcelona to estimate landscape-scale BVOC emission factors in a relatively short period (3 weeks). The two micrometeorological techniques agreed within the uncertainty of the flux measurements at all four sites even though the locations had considerable heterogeneity in species distribution and complex terrain. The observed fluxes were significantly different than emissions predicted with an emission model using site-specific emission factors and land-cover characteristics. Considering the wide range in reported BVOC emission factors of VOCs for individual vegetation species (more than an order of magnitude), this flux estimation technique is useful for constraining BVOC emission factors used as model inputs.
    Atmospheric Measurement Techniques 12/2013; 7(1). · 3.21 Impact Factor
  • Source
    Atmospheric Chemistry and Physics 12/2013; 14:1647-1709. · 5.51 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Organic peroxy (RO2) and hydroperoxy (HO2) radicals are key intermediates in the photochemical processes that generate ozone, secondary organic aerosol and reactive nitrogen reservoirs throughout the troposphere. In regions with ample biogenic hydrocarbons, the richness and complexity of peroxy radical chemistry presents a significant challenge to current-generation models, especially given the scarcity of measurements in such environments. We present peroxy radical observations acquired within a Ponderosa pine forest during the summer 2010 Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics and Nitrogen - Rocky Mountain Organic Carbon Study (BEACHON-ROCS). Total peroxy radical mixing ratios reach as high as 180 pptv and are among the highest yet recorded. Using the comprehensive measurement suite to constrain a near-explicit 0-D box model, we investigate the sources, sinks and distribution of peroxy radicals below the forest canopy. The base chemical mechanism underestimates total peroxy radicals by as much as a factor of 3. Since primary reaction partners for peroxy radicals are either measured (NO) or under-predicted (HO2 and RO2, i.e. self-reaction), missing sources are the most likely explanation for this result. A close comparison of model output with observations reveals at least two distinct source signatures. The first missing source, characterized by a sharp midday maximum and a strong dependence on solar radiation, is consistent with photolytic production of HO2. The diel profile of the second missing source peaks in the afternoon and suggests a process that generates RO2 independently of sun-driven photochemistry, such as ozonolysis of reactive hydrocarbons. The maximum magnitudes of these missing sources (~ 120 and 50 pptv min-1, respectively) are consistent with previous observations alluding to unexpectedly intense oxidation within forests. We conclude that a similar mechanism may underlie many such observations.
    Atmospheric Chemistry and Physics 12/2013; 13(12):31713-31759. · 4.88 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: [1] Three dimensional atmospheric turbulence measurements were conducted from seven sonic anemometers on two different towers in Barrow, AK, during the spring of 2009 as part of the Ocean-Atmosphere-Sea-Ice-Snow (OASIS) campaign. This was the largest number of side-by-side atmospheric turbulence measurements in the Arctic at one time. These analyses allowed for 1) a comparison of the instrumental measurement approaches and 2) a comparison of the variability of the lower atmospheric surface layer at these measurement heights and tower sites. Friction velocity estimates were affected for a sonic anemometer that was operated on the tower in the near vicinity of a building module. Boundary layer height (BLH) was estimated from sonic anemometer measurements based both on a turbulence variable estimator and a temperature gradient method. Results from both methods were compared to radiosonde-estimated BLH and generally underestimated the BLH for shallower depths. Conditions with low BLH (< 100 m) often lasted for several days. The seven ozone depletion events (ODE) that were observed during the OASIS campaign had a tendency of coinciding with BLH of less than 50 m and stable atmospheric conditions; however there was not a clear relationship between the occurrence of ODE and wind speed or wind direction as ODE occurred under a wide range of conditions of BLH, wind speed, local wind direction, and atmospheric stability. Comparisons of these surface layer dynamics to sites in Antarctica and Greenland reveal that boundary layer dynamics are not the primary driving force that fosters the unique ozone chemistry at this coastal Arctic site.
    Journal of Geophysical Research: Atmospheres. 12/2013;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The movement of moisture into, out-of, and within forest ecosystems is modulated by feedbacks that stem from processes which couple plants, soil, and the atmosphere. While an understanding of these processes has been gleaned from Eddy Covariance techniques, the reliability of the method suffers at night because of weak turbulence. During the summer of 2011, continuous profiles of the isotopic composition (i.e., δ18O and δD) of water vapor and periodic measurements of soil, leaf, and precipitation pools were measured in an open-canopy ponderosa pine forest in central Colorado to study within-canopy nocturnal water cycling. The isotopic composition of the nocturnal water vapor varies significantly based on the relative contributions of the three major hydrological processes acting on the forest: dewfall, exchange of moisture between leaf waters and canopy vapor, and periodic mixing between the canopy and background air. Dewfall proved to be surprisingly common (˜30% of the nights) and detectable on both the surface and within the canopy through the isotopic measurements. While surface dew could be observed using leaf wetness and soil moisture sensors, dew in the foliage was only measurable through isotopic analysis of the vapor and often occurred even when no dew accumulated on the surface. Nocturnal moisture cycling plays a critical role in water availability in forest ecosystems through foliar absorption and transpiration, and assessing these dynamics, as done here, is necessary for fully characterizing the hydrological controls on terrestrial productivity.
    Journal of Geophysical Research Atmospheres 09/2013; 118(17):10225-. · 3.44 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Snowpack temperatures from a subalpine forest below Niwot Ridge, Colorado are examined with respect to atmospheric conditions and the 30-min above-canopy and subcanopy eddy covariance fluxes of sensible Qh and latent Qe heat. In the lower snowpack, daily snow temperature changes greater than 1 °C day−1 occurred about 1-2 times in late winter and early spring which resulted in transitions to and from an isothermal snowpack. Though air temperature was a primary control on snowpack temperature, rapid snowpack warm-up events were sometimes preceded by strong downslope winds that kept the night-time air (and canopy) temperature above freezing, thus increasing sensible heat and longwave radiative transfer from the canopy to the snowpack. There was an indication that water vapor condensation on the snow surface intensified the snowpack warm-up.In late winter, we found subcanopy Qh was typically between −10 W m−2 and 10 W m−2 and rarely had a magnitude larger than 20 W m−2. The direction of subcanopy Qh w...
    Journal of Hydrometeorology 08/2013; · 3.27 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present the first eddy covariance flux measurements of volatile organic compounds (VOCs) using a proton-transfer-reaction time-of-flight mass-spectrometer (PTR-TOF-MS) above a ponderosa pine forest in Colorado, USA. The high mass resolution of the PTR-TOF-MS enabled the identification of chemical sum formulas. During a 30 day measurement period in August and September 2010, 649 different ion mass peaks were detected in the ambient air mass spectrum (including primary ions and mass calibration compounds). Eddy covariance with the vertical wind speed was calculated for all ion mass peaks. On a typical day, 17 ion mass peaks including protonated parent compounds, their fragments and isotopes as well as VOC-H+-water clusters showed a significant flux with daytime average emissions above a reliable flux threshold of 0.1 mg compound m-2 h-1. These ion mass peaks could be assigned to seven compound classes. The main flux contributions during daytime (10:00-18:00 LT) are attributed to the sum of 2-methyl-3-buten-2-ol (MBO) and isoprene (50%), methanol (12%), the sum of acetic acid and glycolaldehyde (10%) and the sum of monoterpenes (10%). The total MBO + isoprene flux was composed of 10% isoprene and 90% MBO. There was good agreement between the light and temperature dependency of the sum of MBO and isoprene observed for this work and those of earlier studies. The above canopy flux measurements of the sum of MBO and isoprene and the sum of monoterpenes were compared to emissions calculated using the Model of Emissions of Gases and Aerosols from Nature (MEGAN 2.1). The best agreement between MEGAN 2.1 and measurements was reached using emission factors determined from site specific leaf cuvette measurements. While the modelled and measured MBO + isoprene fluxes agree well the emissions of the sum of monoterpenes is underestimated by MEGAN 2.1. This is expected as some factors impacting monoterpene emissions, such as physical damage of needles and branches due to storms, are not included in MEGAN 2.1. After a severe hailstorm event, 22 ion mass peaks (attributed to six compound classes plus some unknown compounds) showed an elevated flux for the two following days. The sum of monoterpene emissions was 4-23 times higher compared to emissions prior to the hailstorm while MBO emissions remained unchanged. If one heavy storm occurs at this site every month we calculate that the monthly monoterpene emissions (in mg compound m-2) would be underestimated by 40% if this disturbance source is not considered.
    Atmospheric Chemistry and Physics 06/2013; 13(6):15333-15375. · 4.88 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: •We present a multidisciplinary biosphere-atmosphere field campaign.•We measured a gradient from semi-desertic shrublands to wet temperate forests.•A wide range of instruments and vertical platforms were used.•Land cover strongly influenced emissions of BVOCs and gas, energy and water exchange.•Vegetation has strong potential for feed-back to atmospheric chemistry and climate.
    Atmospheric Environment 05/2013; 75:348-364. · 3.11 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The importance of biogenic volatile organic compounds (BVOCs) in understanding of air-quality and climate on regional to global scales has been highlighted in a number of modeling and observational studies. At the same time, another important emerging research topic in atmospheric chemistry is the regional and global impacts of fast growing East Asian megacities. These two research topics must be integrated in order to adequately understand and address air quality challenges emerging from Eastern Asian megacities surrounded by planted or natural forest areas. We present initial measurement results for May, June and September 2011 from the Taehwa Research Forest (TRF) which has been developed to serve as a long term observatory for investigating biosphere–atmosphere interactions at the edge of the Seoul Metropolitan Area (population of ∼23.5 million). The comprehensive measurement datasets of ozone and its precursors such as CO, NOx, SO2 and VOCs shows that high ozone episodes in the suburban site could not be explained by just anthropogenic pollutants alone. In addition, isoprene (C5H8) and monoterpenes (C10H16) were observed as two of the most important OH chemical sinks inside of the forest canopy. In order to understand the impacts of these BVOCs on ozone and related photochemistry, we conducted model sensitivity simulations using a coupled meteorology-chemistry model (WRF-Chem) for conditions including with and without BVOC emissions. The modeling results suggest that BVOC emissions could enhance regional daytime ozone production from 5 to 20 ppbv. The observed temporal variations in ozone correspond well with the variations in BVOCs, which likely reflects the influence of BVOCs on ozone formation. These findings strongly suggest that interactions between anthropogenic pollutants and BVOCs must be understood and quantified in order to assess photochemical ozone formation in the regions surrounding East Asian megacities.
    Atmospheric Environment 05/2013; 70:447–453. · 3.11 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Biogenic volatile organic compound (BVOCs) emissions play an important role in regional air quality and global atmospheric chemistry. In addition, these natural VOC emissions serve important biological functions including attracting and repelling pollinators and herbivores. Some biological organisms use ambient air as a communication medium and the oxidation of these compounds brings about the concentration gradients sensed by insects and other organisms. Isoprene is the predominant BVOC emitted by vegetation and tropical forests are the dominant global source. This compound is very reactive in the atmosphere and contributes to the reactions that control tropospheric oxidant concentrations and thus the concentrations and lifetimes of longer-lived species. This paper presents a study on the seasonal variations in isoprene and some other significant BVOCs such as α-pinene, β-pinene, limonene, e-β ocimene and longifolene, measured at the Guyaflux Tower located in a wet tropical forest in Paracou French Guiana (5o16´54´´N, 52o54´44´´W), during the year of 2011, using the Relaxed Eddy Accumulation technique at approximately 20 meters high above the canopy. The results show a lower concentration of isoprene during the month of February and March which correspond to the wet season with an average of 0,545 μg/m3 and 0,341 μg/m3, respectively followed by a slight increase in middle April (still wet season) and a higher concentration later in mid-June. The same behavior was observed for α-pinene with higher concentrations for the same periods as isoprene however with a smaller increase. All the other compounds had concentrations below 1 μg/m3during the whole year. The monoterpene, e-β ocimene, was observed and is known as a stress compound but the vegetation at the site did not face any known severe stress condition such as excessive drought or flooding. Concerning the fluxes, the results showed that just a small amount of BVOCs were deposited by wet or dry process and the majority of them were released in the atmosphere. Isoprene was by far the biogenic volatile organic compound with the highest concentration and flux, followed by alpha-pinene. The lowest concentration and flux rate for all the studied compounds was observed during the months of March and late July and beginning of August indicating a lower production of those BVOCs by vegetation during those periods. Previous limited studies in Amazonia and the Congo suggested that a higher concentration and flux rate of isoprene and α-pinene should be expected during the dry season with lower emissions during the wet season, which is in relative agreement with what was observed at this tropical forest site in French Guiana. The exceptions were observed in April and June which correspond to a long wet period in which the concentration of isoprene and α-pinene increased more than it was expected for this time of the year. The observations will be compared to output from the global chemistry transport model CAM-chem, which includes the MEGAN biogenic emissions model.
    04/2013;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In this study, the BVOC emissions in November 2010 over the Pearl River Delta (PRD) region in southern China have been estimated by the latest version of a Biogenic Volatile Organic Compound (BVOC) emission model (MEGAN v2.1). The evaluation of MEGAN performance at a representative forest site within this region indicates MEGAN can estimate BVOC emissions reasonably well in this region except overestimating isoprene emission in autumn for reasons that are discussed in this manuscript. Along with the output from MEGAN, the Weather Research and Forecasting model with chemistry (WRF-Chem) is used to estimate the impacts of BVOC emissions on surface ozone in the PRD region. The results show BVOC emissions increase the daytime ozone peak by ~3 ppb on average, and the max hourly impacts of BVOC emissions on the daytime ozone peak is 24.8 ppb. Surface ozone mixing ratios in the central area of Guangzhou-Foshan and the western Jiangmen are most sensitive to BVOC emissions BVOCs from outside and central PRD influence the central area of Guangzhou-Foshan and the western Jiangmen significantly while BVOCs from rural PRD mainly influence the western Jiangmen. The impacts of BVOC emissions on surface ozone differ in different PRD cities, and the impact varies in different seasons. Foshan and Jiangmen being most affected in autumn, result in 6.0 ppb and 5.5 ppb increases in surface ozone concentrations, while Guangzhou and Huizhou become more affected in summer. Three additional experiments concerning the sensitivity of surface ozone to MEGAN input variables show that surface ozone is more sensitive to landcover change, followed by emission factors and meteorology.
    Atmospheric Chemistry and Physics 03/2013; 13(3):6729-6777. · 4.88 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This study investigated the impacts of seasonal and regional variability in biogenic volatile organic compounds (BVOCs) on surface ozone over the Pearl River delta (PRD) region in southern China in 2010 with the WRF-Chem/MEGAN (Weather Research and Forecasting coupled with Chemistry/Model of Emissions of Gases and Aerosols from Nature) modeling system. Compared to observations in the literature and this study, MEGAN tends to predict reasonable BVOC emissions in summer, but may overestimate isoprene emissions in autumn, even when the local high-resolution land-cover data and observed emission factors of BVOCs from local plant species are combined to constrain the MEGAN BVOC emissions model. With the standard MEGAN output, it is shown that the impact of BVOC emissions on the surface ozone peak is ~3 ppb on average with a maximum of 24.8 ppb over the PRD region in autumn, while the impact is ~10 ppb on average, with a maximum value of 34.0 ppb in summer. The areas where surface ozone is sensitive to BVOC emissions are different in autumn and in summer, which is primarily due to the change of prevailing wind over the PRD; nevertheless, in both autumn and summer, the surface ozone is most sensitive to the BVOC emissions in the urban area because the area is usually VOC-limited. Three additional experiments concerning the sensitivity of surface ozone to MEGAN input variables were also performed to assess the sensitivity of surface ozone to MEGAN drivers, and the results reveal that land cover and emission factors of BVOCs are the most important drivers and have large impacts on the predicted surface ozone.
    ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2013; 13:11803-11817. · 5.51 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: At the Rocky Mountain Biogenic Aerosol Study (BEACHON-RoMBAS) field campaign in the Colorado front range, July-August 2011, measurements of gas- and aerosol-phase organic nitrates enabled a study of the role of NOx (NOx = NO + NO2) in oxidation of forest-emitted VOCs and subsequent aerosol formation. Substantial formation of peroxy- and alkyl-nitrates is observed every morning, with an apparent 2.9% yield of alkyl nitrates from daytime RO2 + NO reactions. Aerosol-phase organic nitrates, however, peak in concentration during the night, with concentrations up to 140 ppt as measured by both optical spectroscopic and mass spectrometric instruments. The diurnal cycle in aerosol fraction of organic nitrates shows an equilibrium-like response to the diurnal temperature cycle, suggesting some reversible absorptive partitioning, but the full dynamic range cannot be reproduced by thermodynamic repartitioning alone. Nighttime aerosol organic nitrate is observed to be positively correlated with [NO2] × [O3] but not with [O3]. These observations support the role of nighttime NO3-initiated oxidation of monoterpenes as a significant source of nighttime aerosol. Nighttime production of organic nitrates exceeds daytime photochemical production at this site, which we postulate to be representative of the Colorado front range forests.
    Atmospheric Chemistry and Physics 01/2013; 13(1):1979-2034. · 4.88 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Approximately 70% of Earth's surface is covered by the ocean and the cryosphere. It has been recognized that these environments play an important role in exerting feedbacks on the global climate system. For instance, in the marine boundary layer, it is hypothesized that the emission of biogenic volatile compounds (BVOCs) contributes to cloud formation with resulting changes in temperature and radiation initiating climate feedback. However, measurements of BVOC concentrations are limited, thus the concentration and emission of BVOCs are typically derived and estimated using satellite-observed phytoplankton abundance (i.e., chlorophyll-a concentration). To help validate the modeled relationship between chlorophyll-a concentration and BVOC emission (i.e., isoprene) that current chemistry models are using, BVOCs were measured during the 2012 SHIPPO (SHIp-borne Pole-to-Pole Observations) cruise over the Yellow Sea, the East Sea (or the Sea of Japan), the North Pacific Ocean, and the Bering Sea from 13 July to 29 July. BVOCs were measured using two different methods: Proton Transfer Reaction Mass Spectrometry (PTRMS) and solid absorbent cartridges. The results from these two different measurement techniques will be presented and discussed. In addition, observed BVOC concentrations will be discussed in relation to phytoplankton abundance and other biological and meteorological parameters measured along the cruise track.
    2012 Fall Meeting, AGU; 12/2012
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Biogenic volatile organic compound (BVOC) emissions come from a variety of sources, including living above-ground foliar biomass and microbial decomposition of dead organic matter at the soil surface (litter and soil organic matter). There are, however, few reports that quantify the contributions of each component. Measurements of emission fluxes are now made above the vegetation canopy, but these include contributions from all sources. BVOC emission models currently include detailed parameterization of the emissions from foliar biomass but do not have an equally descriptive treatment of emissions from litter or other sources. We present here results of laboratory and field experiments to characterize the major parameters that control emissions from litter.Litter emissions are exponentially dependent on temperature. The moisture content of the litter plays a minor role, except during and immediately following rain events. The percentage of carbon readily available for microbial and other decomposition processes decreases with litter age. These 3 variables are combined in a model to explain over 50% of the variance of individual BVOC emission fluxes measured. The modeled results of litter emissions were compared with above-canopy fluxes. Litter emissions constituted less than 1% of above-canopy emissions for all BVOCs measured. A comparison of terpene oil pools in litter and live needles with above-canopy fluxes suggests that there may be another canopy terpene source in addition to needle storage or that some terpene emissions may be light-dependent.Ground enclosure measurements indicated that compensation point concentrations of BVOCs (equilibrium between BVOC emission and deposition) were usually higher than ambient air concentrations at the temperature of the measurements.
    Atmospheric Environment 11/2012; 59:302–311. · 3.11 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Volatile organic compound (VOC) mixing ratios measured by five independent instruments are compared at a forested site dominated by ponderosa pine (Pinus Ponderosa) during the BEACHON-ROCS field study in summer 2010. The instruments included a Proton Transfer Reaction Time of Flight Mass Spectrometer (PTR-TOF-MS), a Proton Transfer Reaction Quadrupole Mass Spectrometer (PTR-MS), a Fast Online Gas-Chromatograph coupled to a Mass Spectrometer (GC/MS; TOGA), a Thermal Dissociation Chemical Ionization Mass Spectrometer (PAN-CIMS) and a Fiber Laser-Induced Fluorescence Instrument (FILIF). The species discussed in this comparison include the most important biogenic VOCs and a selected suite of oxygenated VOCs that are thought to dominate the VOC reactivity at this particular site as well as typical anthropogenic VOCs that showed low mixing ratios at this site. Good agreement was observed for methanol, the sum of the oxygenated hemiterpene 2-methyl-3-buten-2-ol (MBO) and the hemiterpene isoprene, acetaldehyde, the sum of acetone and propanal, benzene and the sum of methyl ethyl ketone (MEK) and butanal. Measurements of the above VOCs conducted by different instruments agree within 20%. The ability to differentiate the presence of toluene and cymene by PTR-TOF-MS is tested based on a comparison with GC-MS measurements, suggesting a study-average relative contribution of 74% for toluene and 26% for cymene. Similarly, 2-hydroxy-2-methylpropanal (HMPR) is found to interfere with the sum of methyl vinyl ketone and methacrolein (MVK+MAC) using PTR-(TOF)-MS at this site. A study-average relative contribution of 85% for MVK+MAC and 15% for HMPR was determined. The sum of monoterpenes measured by PTR-MS and PTR-TOF-MS was generally 20-25% higher than the sum of speciated monoterpenes measured by TOGA, which included α-pinene, β-pinene, camphene, carene, myrcene, limonene, cineole as well as other terpenes. However, this difference is consistent throughout the study, and likely points to an offset in calibration, rather than a difference in the ability to measure the sum of terpenes. The contribution of isoprene relative to MBO inferred from PTR-MS and PTR-TOF-MS was smaller than 12% while GC-MS data suggested an average of 21% of isoprene relative to MBO. This comparison demonstrates that the current capability of VOC measurements to account for OH reactivity associated with the measured VOCs is within 20%.
    Atmospheric Chemistry and Physics 10/2012; 12(10):27955-27988. · 4.88 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present a detailed analysis of OH and HO2 observations from the BEACHON (Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics and Nitrogen)-ROCS (Rocky Mountain Organic Carbon Study) 2010 field campaign at the Manitou Forest Observatory (MFO), which is a 2-methyl-3-butene-2-ol (MBO) and monoterpene (MT) dominated forest environment. A comprehensive suite of measurements was used to constrain primary production of OH via ozone photolysis, OH recycling from HO2, and OH chemical loss rates, in order to estimate the steady-state concentration of OH. In addition, the University of Washington Chemical Model (UWCM) was used to evaluate the performance of a near-explicit chemical mechanism. The diurnal cycle in OH from the steady-state calculations is in good agreement with measurement. A comparison between the photolytic production rates and the recycling rates from the HO2 + NO reaction shows that recycling rates are ~20 times faster than the photolytic OH production rates from ozone. Thus, we find that direct measurement of the recycling rates and the OH loss rates can provide accurate predictions of OH concentrations. More importantly, we also conclude that a conventional OH recycling pathway (HO2 + NO) can explain the observed OH levels in this non-isoprene environment. This is in contrast to observations in isoprene-dominated regions, where investigators have observed significant underestimation of OH and have speculated that unknown sources of OH are responsible. The highly-constrained UWCM calculation under-predicts observed HO2 by as much as a factor of 8. As HO2 maintains oxidation capacity by recycling to OH, UWCM underestimates observed OH by as much as a factor of 5. When the UWCM calculation is constrained by measured HO2, model calculated OH is in reasonable agreement with the observed OH levels. Conversely, constraining the model to observed OH only slightly reduces the model-measurement HO2 discrepancy, implying unknown HO2 sources. These findings demonstrate the importance of constraining both the inputs to, and recycling within, the ROx radical pool (OH + HO2 + RO2).
    Atmospheric Chemistry and Physics 06/2012; 12(6):15945-15975. · 4.88 Impact Factor

Publication Stats

1k Citations
260.56 Total Impact Points

Institutions

  • 2005–2014
    • National Center for Atmospheric Research
      • Division of Atmospheric Chemistry
      Boulder, Colorado, United States
  • 2002–2008
    • University of Colorado at Boulder
      • Department of Ecology and Evolutionary Biology (EBIO)
      Boulder, CO, United States
  • 2007
    • National Research Center (CO, USA)
      Boulder, Colorado, United States
  • 1999
    • University of Colorado
      Denver, Colorado, United States