A31A-0054
Methanol and other VOC fluxes from a Danish beech forest during springtime
In-canopy mixing ratio gradients and above-canopy fluxes of several volatile organic compounds (VOCs) were measured using a commercial proton transfer reaction mass spectrometer (PTR-MS) in a European beech (Fagus sylvatica) forest in Denmark. Emission fluxes of methanol occurred dominantly late at night, which was supported by highest mixing ratios in the crown region, and is in line with recent controlled laboratory experiments. Also confirming previous measurements, monoterpene emissions showed a diurnal cycle consistent with light-dependent emissions, supported by highest mixing ratios in the canopy space during early afternoon. Also emitted was acetone, but only at ambient temperatures exceeding 20 °C. Deposition dominated at lower temperatures. Deposition fluxes occurred also for methanol but seemingly as a result of high ambient methanol mixing ratios. Our in-canopy gradient measurements contrasted earlier results from tropical and pine forest ecosystems in that they did not show this beech ecosystem to be a strong sink for oxygenated VOCs. Instead, their gradients were flat and only small deposition velocities (<0.1 cm s-1) were observed to the onsite soil. However, as soil uptake was consistent and appeared to be related to soil moisture, more measurements are needed to evaluate the soil sink strength as a function of physical and biological paramaters. In turn, as canopy scale fluxes are net fluxes with emissions from photosynthesizing leaves affecting potential oxygenated VOC uptake, only independent, controlled laboratory experiments may be successful in separating stomatal from non-stomatal fluxes, and emission from deposition.
A31A-0055
Seasonal variation of biogenic methanol fluxes from a southeastern deciduous forest
Methanol emissions from plants play major roles in Earth's chemistry and climate. These emissions also serve as vital indicators of plant function and stress physiology. We studied biogenic methanol emissions from both determinate late-successional and indeterminate early- successional tree species at the Pace flux tower at the Virginia Forest Research Facility (VFRF). We examined seasonal regulation over methanol emissions and correlated these emissions with environmental data such as PAR, temperature, and humidity. Monitoring emissions from single branches throughout the growing season and during leaf senescence yielded unique information on annual patterns of emission and how they vary between plant functional groups. These data are helpful for developing predictive emission models and for our understanding of how methanol emission will affect (and be affected by) global environmental change.
A31A-0056
Methyl Chavicol: Characterization of its Biogenic Emission Rate, Abundance, and Oxidation Products in the Atmosphere
We report quantitative measurements of ambient atmospheric mixing ratios for methyl chavicol and determine its biogenic emission rate. Methyl chavicol, a biogenic oxygenated aromatic compound, is abundant within and above Blodgett Forest, a ponderosa pine forest in the Sierra Nevada Mountains of California. Methyl chavicol was detected simultaneously by three in-situ instruments: gas chromatograph with mass spectrometer detector (GC-MS), proton transfer reaction mass spectrometer (PTR-MS), and thermal desorption aerosol GC-MS (TAG). Previously identified as a potential bark beetle disruptant, methyl chavicol atmospheric mixing ratios are strongly correlated with 2-methyl-3-buten-2-ol (MBO), a light and temperature dependent biogenic emission from the ponderosa pine trees at Blodgett Forest. Scaling from this correlation, methyl chavicol emissions account for 4-68 % of the carbon mass emitted as MBO in the daytime, depending on the season. From this relationship, we estimate a daytime basal emission rate of 0.72-10.2 μ gCg-1h-1, depending on needle age and seasonality. We also present the first observations of its oxidation products (4-methoxybenzaldehyde and 4-methyoxy benzene acetaldehyde) in the ambient atmosphere. Methyl chavicol is a major essential oil component of many species. We propose this newly- characterized biogenic compound should be included explicitly in both biogenic volatile organic carbon emission and atmospheric chemistry models.
A31A-0057
Emissions and Photochemistry of BVOCs in a Ponderosa Pine woodland
We deployed two proton-transfer-reaction mass spectrometry instruments (PTR-MS, IONICON ANALYTIK) for ambient and branch enclosure measurements at the Manitou Experimental Forest, located in the Southern Rocky Mountain area as a part of the Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics and Nitrogen (BEACHON) field campaign in 2008. Vegetation at the field site is dominated by Ponderosa Pine. BVOC emissions from Ponderosa Pine along with temperature, photosynthetic photon flux density (ppfd), relative humidity, and CO2 uptake were measured from two branch-enclosures (shade and sun). Diurnal variations and the emission response to environmental conditions are described and compared to existing models. In addition, we analyzed the speciation of BVOCs from enclosures by GC-MS. We will present quantitative and qualitative characteristics of BVOC emissions from Ponderosa Pine and analytical characteristics of PTR-MS such as fragmentation patterns of semi-volatile compounds (sesquiterpene, bornyl acetate etc) that we identified as major emissions from the enclosures. BVOC emissions observed in the enclosures will be quantitatively compared to BVOC distributions in ambient air. We explore the presence of possibly unidentified BVOCs in the forest canopy by examining PTR-MS mass spectra of enclosure and ambient air samples based on mass scans between 40 - 210 amu.
A31A-0058
Estimation of Biogenic VOC Emissions From Ecosystems in the Czech Republic
Volatile organic compounds (VOC) are one of the crucial elements in photochemical reactions in the atmosphere which lead to tropospheric ozone formation. While modelling concentration of low-level ozone proper information about VOC sources and sinks is necessary. VOC are emitted into the atmosphere both from anthropogenic and natural sources. It has been shown in previous studies (e.g. Simpson et al, 1995) that contribution of volatile organic compounds emitted from biogenic sources to total amount of VOC in the atmosphere can be significant. Our work focuses on estimation of VOC emissions from natural ecosystems, most importantly from forests, and its application in photochemical modelling. Preliminary results have shown that inclusion of biogenic emissions in model input data leads to improvement of resulting ozone concentration which encouraged us to work on detailed biogenic VOC emission estimation. Using grid of 1x1km CORINE Land Cover over the area of the Czech Republic, emissions from deciduous, coniferous and mixed forests were estimated aplying the algorithm of Guenther et al., 1995. According to data from Forest Management Institute each cell of model grid has been assigned a proportional composition of each of thirteen tree species which are the the main forest constituents in the Czech Republic. Aggregating data of tree species composition with land cover category emission factor of particular chemical compound (isoprene, monoterpenes) has been obtained for each cell. Annual emissions of VOC on hourly basis have been calculated for domain of the Czech Republic. Biogenic emissions of isoprene and monoterpenes were compared with the emission inventory of anthropogenic sources. The inventory is provided by Czech Hydrometeorological Institute and covers emissions from major stationary sources, area sources (including domestic heating) and mobile sources. Our results show that natural emissions are approximately half the amount of organic compounds emitted from anthropogenic sources. References: - Simpson D., Guenther A., Hewit C.N. and Steinbrecher R., 1995. Biogenic emissions in Europe. 1. estimates and uncertainties. J. Geophys. Res. 100(D11), 22875-22890. - Guenther A., Hewitt N., Erickson D., Fall R., Geron Ch., Graedel T., Harley P., Klinger L., Lerdau M., McKay W. A., Pierce T., Scholes B., Steinbrecher R., Tallamraju R., Taylor J., Zimmerman P., 1995. Global model of natural organic compound emissions. J. Geophys. Res. 100, 8873-8892.
A31A-0059
Determination of Isomer-Specific Isoprene Nitrate Production Yields and Ozone Rate Constants
Isoprene nitrates are produced from the reaction of isoprene, the dominant biogenic volatile organic compound emission, with OH and NO in the atmosphere. Determining the identity, yields, and atmospheric lifetimes for the 8 isomers is important, as the reactivity and thus fate of the individual nitrates is expected to vary widely. The reaction products of the isoprene nitrate isomers with OH and ozone are important because of the potential loss of the nitrate group, which could be dependent on the isomeric structure, making the production yields of the individual isomers vital to the understanding of ozone/NOx chemistry. Here we report the individual identities, yields, and ozone rate constants for the isoprene nitrate isomers.
A31A-0060
Measurements of the yields of methacrolein and methyl vinyl ketone from the OH-initiated oxidation of isoprene under NOx free conditions.
The chemical mechanism for the oxidation of isoprene is a subject of considerable interest in atmospheric chemistry. Isoprene, the dominant natural hydrocarbon emitted into the atmosphere by deciduous trees, can contribute significantly to the production of ozone, organic nitrates, and secondary VOCs in the troposphere because of its high reactivity with the hydroxyl radical (OH). The accuracy of urban and regional air quality models depends on a complete understanding of the mechanism of isoprene oxidation and the product branching ratios under atmospheric conditions. Recent measurements of OH and HO2 radicals in forest environments show serious discrepancies with modeled concentrations of these radicals, bringing into question our understanding of the atmospheric chemistry of isoprene and other reactive biogenic emissions. A small UV-irradiated reaction chamber was coupled to an on-line mass spectrometer to investigate the formation of isoprene oxidation products under NOx free conditions. UV-photolysis of hydrogen peroxide (H2O2) was employed as the OH precursor to initiate the oxidation of isoprene. During experiments carried out at 50°C and various concentrations of H2O2, yields of methacrolein (MAC) and methyl vinyl ketone (MVK) were derived from their time-resolved concentration profiles. The measured yields exhibit a strong dependence on the initial concentration of H2O2 and decrease with increasing H2O2, suggesting that the relative yields of MVK and MAC depend on the concentration of radicals. Experimental concentration profiles were compared to model predictions to test current mechanisms of isoprene chemistry. In addition, preliminary measurements of the temperature dependence of the MAC and MVK yields over the temperature range of 30-70°C will be presented.
A31A-0061
Nocturnal isoprene oxidation by NO3: The role of fine-scale mixing and transport within the nocturnal boundary layer studied by vertical profiling from a tall tower
Isoprene is the most abundant biogenic VOC. Because it is emitted during daytime, it is mainly oxidized by photochemically formed hydroxyl radicals (OH), but significant concentration levels can be still present after sunset. If NOx is available, this isoprene can undergo rapid nocturnal oxidation by NO3. However, nocturnal NO3-driven oxidation depends on the fine-scale vertical stratification and mixing, since the sources of these species are not necessarily co-located and mixing at night is not efficient.Nocturnal vertical profiles of nitrate oxide species including the nitrate radical, NO3, and VOCs including isoprene were measured using a 300 m tower in Erie, Colorado, in summer 2007. The analysis of the nighttime data shows distinctive layered structures of nitrogen oxides and VOCs with typical layer thicknesses of 40 to 100 m. Trace gas concentrations were highly variable between different layers with peak values of e.g. NO3 concentration of a few hundred pptv within the altitude range of the tower. Isoprene concentration were typically persistent throughout the nighttime hours, and its vertical distribution showed a negative gradient over altitude. Steady state lifetime analysis of the NO3 radical showed that 60 to 70% of the NO3 produced was removed via reaction with isoprene, except for a shallow surface layer in which NO was present. In addition, the persistent presence of isoprene suggests that isoprene was transported from a NOx poor area to the measurement site. By using isoprene oxidation products from daytime OH oxidation as a tracer for isoprene concentrations before sunset and therefore the start of nighttime oxidation with NO3, the fraction of isoprene that had been oxidized by NO3 since sunset during transport from its reservoir to the measurement site could be estimated to approximately 50%.
A31A-0062
Observed secondary organic aerosol (SOA) and organic nitrate yields from NO3 oxidation of isoprene
Formation of organic nitrates and secondary organic aerosol (SOA) from the NO3 oxidation of isoprene has been studied at atmospheric concentrations of VOC (10 ppb) and oxidant (<100 ppt NO3) in the presence of ammonium sulfate seed aerosol in the atmosphere simulation chamber SAPHIR at Forschungszentrum Jülich. Cavity Ringdown (CaRDS) and thermal dissociation - CaRDS measurements of NO3 and N2O5 as well as Thermal Dissociation - Laser Induced Fluorescence (TD-LIF) detection of alkyl nitrates (RONO2) and Aerodyne Aerosol Mass Spectrometer (AMS) measurements of aerosol composition were all used in comparison to a Master Chemical Mechanism (MCM) based chemical kinetics box model to quantify the product yields from two stages in isoprene oxidation. We find significant yields of organic nitrate formation from both the initial isoprene + NO3 reaction (71%) as well as from the reaction of NO3 with the initial oxidation products (30% - 60%). Under these low concentration conditions (~1 μg / m3), measured SOA production was greater than instrument noise only for the second oxidation step. Based on the modeled chemistry, we estimate an SOA mass yield of 10% (relative to isoprene mass reacted) for the reaction of the initial oxidation products with NO3. This yield is found to be consistent with the estimated saturation concentration (C*) of the presumed gas products of the doubly oxidized isoprene, where both oxidations lead to the addition of nitrate, carbonyl, and hydroxyl groups.
A31A-0063
Secondary Organic Aerosol (SOA) Formation From the NO3 Radical Oxidation of Alpha- pinene
Terpenes such as alpha-pinene, emitted in large quantities from vegetation into the troposphere, are well known to react with O3, OH and NO3 radicals leading to the formation of secondary organic aerosol, SOA. While particle formation and growth from the NO3 reaction with alpha-pinene have been reported by a number of groups, as have the gas phase products of this reaction, little is known about the chemical composition of the particles. We report studies of the composition of particles formed in the NO3 – alpha- pinene reaction using two reactors, a flow tube and a static chamber. Nitrate radicals were generated in the flow tube by the reaction of NO2 with O3 and in the static chamber by the thermal decomposition of N2O5. Particle formation and growth was monitored using SMPS and APS. A variety of analytical techniques were applied to measure the chemical composition, including FTIR of particles collected on ZnSe impactor discs, and GC-MS, ESI-MS, APCI-MS, HPLC-MS and HPLC-UV of samples collected on quartz fiber filters. In addition, particle mass spectrometer techniques including AMS and SPLAT provided real-time analysis. A number of organic nitrates were observed in the particles, along with carbonyl compounds and organic acids. Gas phase products measured using DNPH coated-cartridges included pinonaldehyde, formaldehyde, acetaldehyde and acetone. Results of studies in which concentrations of the reactants were varied will be presented and possible mechanisms and the atmospheric implications will be discussed.
A31A-0064
Photodegradation of SOA Prepared by Oxidation of d-Limonene by Ozone and NO3
Terpenes account for over 50% of biogenically emitted volatile organic compounds (VOC). Terpenes including limonene react with gas phase oxidants in the air such as NO3, ozone and OH. Secondary organic aerosol (SOA) is formed when low vapor pressure products spontaneously condense into particles. While in the atmosphere, SOA age via heterogeneous atmospheric chemistry, often with profound effects on the physical and chemical properties of the particles. The primary goal of this research is to study the photochemical aging of monoterpene-derived aerosol particles. SOA particles are generated in the lab by reacting limonene and oxidants including ozone and NO3 in a Teflon reaction chamber. The concentrations of limonene and oxidants were set to different levels in experiments. The particles are collected on filters and irradiated with light in the actinic region (>290 nm). The gas-phase photolysis products were studied using chemical ionization mass spectrometry (CIMS) in real time. The results show that the photodegradation of limonene SOA strongly depends on radiation wavelengths. SOA photodegradation mechanisms and their implications for photochemical aging of organic aerosols will be discussed.
A31A-0065
Formation of High-yield Hydrogen Peroxide and Unexpected Carbonyl Compound in Aqueous Phase Ozonolysis of Alpha-Pinene and Beta-Pinene
An increasing amount of attention has been paid to the important role of aqueous phase reactions in the formation of second organic aerosol (SOA) and the transformation of oxidants in the troposphere. However, compared with their gas phase chemistry, the aqueous phase reaction mechanisms of organic compounds are ambiguous and not all the products are identified, especially for the peroxides and carbonyl compounds. In this study, the aqueous phase ozonolysis of alpha-pinene and beta-pinene, one of the most abundant biogenic organic compounds, were simulated at different pHs and temperatures in laboratory considering tropospheric conditions. We determined three kinds of products, including peroxides, carbonyl compounds and organic acids. The results are as follows: (i) for both alpha-pinene--O3 and beta-pinene--O3, the hydrogen peroxide was determined with the yield approaching 100%; (ii) for alpha-pinene--O3, HCHO was not detected, while unexpected carbonyl compounds were observed; for beta-pinene--O3, HCHO was determined with a high yield; and (iii) for both alpha-pinene--O3 and beta-pinene--O3, organic acids were not detected. We suggest that these results can help to deduce the detailed mechanisms of ozonolysis of alpha-pinene and beta-pienne in the aqueous phase and also to better understand the formation of SOA. Moreover, this high-yield hydrogen peroxide implies that the two reactions mentioned above potentially contribute a considerable amount of peroxide to the cycle of oxidants in the tropospheric aqueous phase in humid regions.
A31A-0066
The Influence of Relative Humidity on the SOA-Formation at Various Temperatures
Monoterpenes represent a significant fraction of biogenic originated volatile organic compounds in the atmosphere. The oxidation of monoterpenes by ozone, OH and NO3 radicals has been identified as a significant source for secondary organic aerosols (SOA) in the atmosphere. SOA yields can depend on relative humidity, temperature and pre-existing particulate organic mass for the absorption of the respective oxidation products. In this study, we investigated the SOA-yields of the ozonolysis of a-pinene and limonene under dry and humid conditions in the aerosol chamber AIDA at temperatures of 303 and 243 K. All experiments were carried out in the presence of 500 ppm cyclohexane to scavenge OH-radicals produced during the reaction. In excess of ozone, the monoterpene was added to the chamber in steps. From this procedure the SOA yield, using the increasing organic aerosol mass, was determined. The monoterpenes and their oxidation products in the gas phase were measured by proton-transfer-reaction mass-spectrometry. The aerosol phase was characterized by means of an aerosol mass spectrometer (AMS). Size distributions of the organic aerosol were measured with differential mobility particle sizer. The resulting SOA mass concentrations were related to the consumed monoterpene mass on a basis 5 min. time resolution, which provided time dependent growth functions. We observed significant lower SOA yields under dry conditions especially at lower temperatures. The AMS measurements revealed that partitioning of water to the aerosol phase is small and cannot account for the increase in SOA yields in the humid case. Molar yields of the a-pinene oxidation products pinonaldehyde and acetone increase with humidity. At temperatures below 253 K pinonaldehyde is exclusively found in the condensed phase and contributes then significantly to the SOA mass. In addition the water vapor dependent channels in the mechanism lead to other low volatile products resulting in higher SOA yields under humid conditions
A31A-0067
HR-ToF-AMS Study of the Yield and Chemical Composition of alpha-pinene SOA as a Function of Organic Loading
We have investigated the yield and chemical composition of α-pinene SOA. For the lowest loadings studied (0.15 to 2μg m-3) we observe a step-like increase in the SOA mass yields with loading. Furthermore, we observe significant SOA formation for reacted α-pinene concentrations as low as 0.3 ppbv while literature data suggest that no SOA formation will occur for reacted α-pinene concentrations below 1 ppbv. HR-ToF-AMS results indicate that the chemical composition of the aerosol is a strong function of the organic particulate loading. High-resolution analysis shows that the oxygen-to-carbon atomic ratio of the organic material increased at low loading while the atomic hydrogen-to-carbon ratio decreased. The atomic ratios were accurately parameterized by a four-product basis set of decadal volatility (viz. 0.1, 1.0, 10, 100 μg m-3) employing products with the empirical formulas C1H1.32O0.48, C1H1.36O0.39, C1H1.57O0.24, and C1H1.76O0.14. These findings suggest considerable caution is warranted in the extrapolation of laboratory results that were obtained under conditions of relatively high loading (i.e., >15μg m-3) to modeling applications relevant to the atmosphere, for which loadings of 0.1 to 20 μg m-3 are typical. For the lowest loadings, the particle mass spectra resembled observations reported in the literature for some atmospheric particles.
A31A-0068
Quantitative Analysis of Isomeric Volatile Organic Compounds in a Northern Hardwood Forest by Proton Transfer Reaction Linear Ion Trap (PTR-LIT) Mass Spectrometry
Several low molecular weight, isomeric volatile organic compounds (VOCs) occur in the atmosphere in the low ppb to ppt range, including methyl vinyl ketone (MVK) and (MACR) from isoprene oxidation, and aerosol precursor monoterpenes and sesquiterpenes. Although proton transfer reaction mass spectrometry (PTR- MS) quantifies VOCs with low ppt limits of detection (LOD), it cannot differentiate isomers or isobaric molecules. A proton transfer reaction – linear ion trap (PTR-LIT) mass spectrometer was developed and utilized to quantify and distinguish isomers as well as test for interferants by allowing for MSn experiments while retaining LOD in the 100 ppt range for most compounds. The PTR-LIT was deployed at the PROPHET tower site at the University of Michigan Biological Station (UMBS) from July to mid-August 2008 to sample air above a mixed deciduous/coniferous forest canopy. The extended capabilities of the PTR-LIT were used to address local ozone formation from the oxidation of isoprene by monitoring speciated MVK and MACR. Good agreement existed between [MVK+MACR] in MS1 mode and [MVK] + [MACR] in MS2 mode. Possible interferences at common masses were directly addressed by comparing the MS2 spectra of atmospheric masses to those of standards. Aerosol formation and size distribution data were compared to VOC oxidation. In particular isoprene oxidation was monitored by using MVK, MACR, and glyoxal, a fifth generation oxidation product. Furthermore, total monoterpene concentration was monitored and oxidation rates were calculated. Finally, total sesquiterpenes were not observed above the limit of detection making them an unlikely source for either aerosol growth or the missing OH reactivity previously observed at UMBS.
A31A-0069
Determination of Reactive Nitrogen Species (NOx, NOy-HNO3, Peroxyacetyl Nitrates, Total Organic Nitrates) During the PROPHET Summer 2008 Intensive
Determinations of NOx, NOy-HNO3, peroxyacetyl nitrates (PANs) and total organic nitrates (∑RONO2) were made during the summer 2008 intensive of the Program for Research on Oxidants: Photochemistry, Emissions and Transport (PROPHET). The Total Reactive Nitrogen Instrument (TRENI), a high sensitivity instrument, is capable of speciating atmospheric nitrogen species. TRENI, a chemiluminescence analyzer with two inlet systems (photolytic cell and heated gold tube) was employed to quantify NO, NO2 and NOy. Another inlet system comprised of thermal dissociation reactors, was employed to speciate NOy components into NOx, PANs and ∑RONO2. The detection limit of TRENI is 5 ppt for NOx and NOy and 20 ppt for total organic nitrates and PANs. In this study, we examine the extent to which we can explain the ∑RONO2 concentrations with known precursors and/or individual RONO2 measurement data. The observed fraction of NOy attributable to the ∑RONO2 is much higher than from previous individual RONO2 measurements. It seems clear that there is a large component of 'missing NOy' in the ∑RONO2 channel, as observed by others using the thermal dissociation inlet approach. We also examine here the potential sources of the frequently observed morning pulse of NOx, and the potential role of the forest canopy in mediating nitrogen chemistry.
A31A-0070
Hydroxyl and Hydroperoxy Radical Measurements in a Forested Environment During the PROPHET 2008 and NIFTy Field Campaigns
Hydroxyl (OH) and hydroperoxy (HO2) radicals are key species driving the gas-phase oxidation of organic trace gases and thus control the lifetime of greenhouse gases, tropospheric ozone production, and secondary organic aerosol formation. Recent measurements of HOx (OH + HO2) radicals in forest environments show serious discrepancies with modeled concentrations of these radicals, including high nighttime concentrations of OH, bringing into question our understanding of the atmospheric chemistry of isoprene and other reactive biogenic emissions. During the summer 2008, additional measurements of HOx radicals in a forest environment were made at the PROPHET (Program for Research on Oxidants: PHotochemistry, Emissions, and Transport) site in northern Michigan, as well as in central Indiana as part of the NIFTy (Nucleation in ForesTs) campaign using a laser-induced fluorescence instrument developed at Indiana University. A suite of other measurements including volatile organic compounds (VOCs), nitrogen oxides (NOx), ozone, CO, and UV actinic flux were measured simultaneously at PROPHET 2008 and will aid in comparing the measured HOx concentrations with those observed during the previous PROPHET field campaigns. During PROPHET 2008, measurements were made both above the forest canopy as well as below canopy at the surface. The ground level measurements from PROPHET 2008 and NIFTy will be compared to above canopy concentrations at PROPHET and used to investigate the processes driving the HOx chemistry inside the canopy.
A31A-0071
Measurements of Total Hydroxyl Radical Reactivity in Forested Environments with a Turbulent-Flow Reactor
Biogenic volatile organic compounds (BVOCs) play a significant role in the gas-phase chemistry that occurs within forested environments. Measurements of total hydroxyl radical (OH) reactivity in forested environments have found discrepancies between measured values and those calculated from collocated measurements of VOC concentrations. This suggests the presence of highly-reactive undetected BVOCs that have not been detected with current instrumentation. Additional measurements of total OH reactivity together with measurements of BVOCs are need to further characterize these missing BVOCs and to further constrain atmospheric chemistry models. We have constructed an instrument based on the Total OH Loss rate Method (TOHLM) that operates under turbulent flow conditions, with Reynolds numbers between 5000 and 6000. This instrument has been characterized in the laboratory and deployed at the 2008 Nucleation In ForesT Environments (NIFTy) campaign in southern Indiana and the Program for Research on Oxidants: PHotochemistry, Emission, and Transport (PROPHET) 2008 campaign in northern Michigan. We will describe our improvements to the TOHLM technique, and results from the laboratory characterization will be presented. In addition, surface measurements of total OH reactivity from the NIFTy and PROPHET campaigns will be presented and discussed.
A31A-0072
Initial Measurements of Radiocarbon In Atmospheric Formaldehyde at Narragansett, RI
Formaldehyde is an intermediate in the atmospheric oxidation of nearly every volatile organic compound (VOC) and is important to odd-hydrogen radicals and ozone chemistry. It is directly observed from space and its distributions are used to constrain biogenic emissions of VOCs, specifically isoprene. The relative contribution of fossil VOCs and biogenic VOCs to formaldehyde, to isoprene emission estimates and subsequently to ozone and oxidant chemistry is expected to vary seasonally and spatially due to VOC speciation, emission patterns, and reactivity. The radiocarbon, 14C, content of formaldehyde is useful in assessing the relative contributions of fossil and biogenic VOC groups to formaldehyde. We report a compound specific radiocarbon analysis (CSRA) method for formaldehyde based upon gaseous formaldehyde collection, derivatization to thiazolidine, preparative capillary gas chromatography separation, and AMS analysis. Ambient measurements from Narragansett, RI, made in winter and summer 2007 are presented. On 11 of 13 samples, we find 80 to >95% of the collected formaldehyde is of fossil origin and, contrary to our initial hypothesis, we see no seasonal shift in proportion. The remaining 2 samples, one each from winter and summer, are 30-40% biogenic carbon. The measurements are interpreted considering fossil-biogenic source attribution and local transport conditions and contrasted with prior measurements from Nova Scotia. Further, CSRA measurement of acetaldehyde is feasible with the method.
A31A-0073
Radiocarbon Analysis of Elemental Carbon and Total Organic Carbon in Atmospheric Aerosols Collected at Cape Hedo, Okinawa, Japan
A study was initiated to understand the sources and behaviors of carbon-containing compounds in the atmospheric aerosols in East Asian region. As an initial attempt, we collected airborne particulate matter (APM) with diameter <10 micrometer (PM10) in Okinawa, Japan and analyzed 14C/12C ratio in EC and total organic carbon (TOC) to apportion source of biomass and fossil fuel combustion in PM10 aerosols. Okinawa is situated approximately 1500 km south of Tokyo, Japan, 2000 km southeast of Beijing, China, and 1000 km south of South Korea. Its location in Asia is well suited for studying long-range transport of air pollutants in East Asia. Aerosol particles were collected at the Cape Hedo Atmosphere and Aerosol Monitoring Station (CHAAMS) in Okinawa, Japan. Each sample was collected for two weeks with a high-volume air sampler at a rate of 1000 L min-1 to collect aerosol particles on a quartz filter, which was pre-combusted before use to eliminate residual organic compounds. Radiocarbon is measured in AMS facility (NIES-TERRA) at National Institute for Environmental Studies after preparing graphite. The results showed that during Asian dust events in March and April, both APM and EC in PM10 aerosols collected in Okinawa, Japan were much higher than those of non-Asian dust event. The percent modern carbon (pMC) of EC and TOC was much smaller for the PM10 aerosols collected during Asian dust events than those of non-dust event. When maritime air mass prevailed, biomass originated organic compounds were the major TOC in the aerosols. We will report data on 14C/12C ratio of EC and TOC in PM10 aerosols collected at CHAAMS during March to October, 2008
A31A-0074
Real-Time Detection and Mixing-State of Methanesulfonic Acid in Single Aerosol Particles During a Phytoplankton Bloom
Methanesulfonic acid (MSA) derives from the oxidation of dimethyl sulfide (DMS), which is produced by oceanic phytoplankton. Unique oceanic biological conditions, in the summer of 2005 off the California coast, resulted in the production of high levels of atmospheric MSA in the aerosol phase. These oceanic emissions were transported with daily westerly winds from the coast approximately 60 miles inland to Riverside. The MSA-containing particles were detected during the Study of Organic Aerosols in Riverside, CA from July- August 2005 (SOAR-1) in submicron and supermicron particles (0.2-3.0 μm) using real-time, single particle mass spectrometry. The single particle mixing-state of MSA-containing particles is reported wherein MSA was found to partition onto both local and transported particle types detected in Riverside. Interestingly, the relative amount of MSA on vanadium particles was ~3 times greater than other particle types, suggesting a possible catalytic role of vanadium in atmospheric MSA formation. This poster will present the results from the summertime study, as well as provide a discussion of the implications of these findings.
A31A-0075
Determination of Dicarboxylic Acid Concentrations in Surface Microlayer of Dams in Okinawa, Japan
The surface microlayer (SML) is a thin layer that forms the boundary between atmosphere and water body. The SML includes fatty acid, protein and other organic compounds. It is the site across which the atmosphere-water system interacts. It also has unique chemical, physical and biological properties, which are very different from those of the underlying water. We determined concentrations of dicarboxylic acids (oxalic, malic, malonic, succinic, adipic, phthalic, fumaric, and maleic acids) in the SML, and compared with those of underlying bulk water. Dicarboxylic acids are the major organic compounds found in atmospheric aerosols, which can be derived from the wind-blown SML. The sampling sites we chose were dams in Okinawa, Japan. The SML was sampled by using a glass plate method. Concentrations of dicarboxylic acids were determined by using a GC-FID after derivatization. The results showed that the dicarboxylic acid concentrations were 2- 17 times higher than those of the underlying water. We have also found that the concentrations of some of the dicarboxylic acids were lower in the afternoon than those in the morning at the same sampling site.