A31B-0076
Examining the Temperature Dependence of E85 Versus Gasoline Emissions on Air Pollution With a Near-Explicit Chemical Mechanism
The increased use of ethanol in transportation fuels warrants an investigation of its consequences. An important component of such an investigation is the temperature-dependence of ethanol and gasoline exhaust chemistry. We use the near-explicit Master Chemical Mechanism (MCM, version 3.1, LEEDS University) with the SMVGEAR II chemical ordinary differential solver to provide the speed necessary to simulate explicit chemistry. The MCM has over 13,500 organic reactions and 4,600 species. SMVGEAR II is a sparse-matrix vectorized Gear solver that reduces the computation time significantly while maintaining any specified accuracy. We use species-resolved tailpipe emissions data for E85 and gasoline vehicles to compare the impact of each on ozone and carcinogenic organic species as a function of ambient temperature and backgound concentrations. We find that, in most cases, an increase in temperature increases ozone more with E85 than with gasoline. Also, average ozone concentrations through the range of temperatures tested are higher with E85 than with gasoline.
A31B-0077
Diagnostic Modeling of PAMS VOC Observation on Regional Scale Environment
While a number of gas-phase chemical mechanisms, such as CBM-Z, RADM2, SAPRC-07 had been successful in studying gas-phase atmospheric chemical processes they all used some lumped organic species to varying degrees. Photochemical Assessment Monitoring Stations (PAMS) has been in use for over ten years and yet it is not clear how the detailed organic species measured by PAMS compare to the lumped model species under regional-scale transport and chemistry interactions. By developing a detailed mechanism specifically for the PAMS organics and embedding this diagnostic model within a regional-scale transport and chemistry model we can then directly compare PAMS observation with regional-scale model simulations. We modify one regional-scale chemical transport model (Taiwan Air Quality Model, TAQM) by adding a submodel with chemical mechanism for interactions of the 56 species observed by PAMS. This submodel then calculates the time evolution of these 56 PAMS species within the environment established by TAQM. It is assumed that TAQM can simulate the overall regional-scale environment including impact of regional-scale transport and time evolution of oxidants and radicals. Therefore we can scale these influences to the PAMS organic species and study their time evolution with their species-specific source functions, meteorological transport, and chemical interactions. Model simulations of each species are compared with PAMS hourly surface measurements. A case study located in a metropolitan area in central Taiwan showed that with wind speeds lower than 3 m/s, when meteorological simulation is comparable with observation, the diurnal pattern of each species performs well with PAMS data. It is found that for many observations meteorological transport is an influence and that local emissions of specific species must be represented correctly. At this time there are still species that cannot be modeled properly. We suspect this is mostly due to lack of information on local variations on emissions.
A31B-0078
Diurnal and Seasonal Variability of Gasoline-Related Volatile Organic Compounds in Riverside, CA
On and off-road mobile source emissions are the dominant contributor to urban anthropogenic volatile organic compound (AVOC) emissions. Analyses of speciated gasoline samples from California for both summer and winter indicate significant differences in chemical composition due to intentional seasonal adjustments to liquid fuel composition. Ambient air measurements of ~60 compounds, including VOCs, were measured via in-situ gas chromatography during the Study of Organic Aerosols at Riverside (SOAR) 2005 for both summer and fall. A chemical mass balance analysis was used to differentiate evaporative and tailpipe VOC emissions from motor vehicles. Overall, evaporative emissions accounted for 31 ± 2% of gasoline emissions in Riverside, CA. The California Air Resources Board (CARB) EMFAC model similarly estimates 39% of gasoline engine-related VOC emissions are due to evaporative sources for Riverside County. Diurnal evaporative emission source contributions are relatively stable around 10 ug/m3, while tailpipe emissions peak at ~60 ug/m3 during the morning commuter peak period and lack a peak in emissions during the afternoon commute due to rapid dilution associated with high afternoon vertical mixing heights and wind speeds in the Riverside area. The relative increases in ambient VOC and carbon monoxide concentrations during pollution events are consistent with CARB's 2005 emission inventory; we calculated 0.086 ± 0.006 mass of VOC emissions to mass of CO emissions compared to 0.105 in the emission inventory.
A31B-0079
Dependence of Precursor and OH on the Oxygenated SOA: Experimental Potential Aerosol Mass Chamber Studies
The dependence of the formation and aging of secondary organic aerosol (SOA) is studied from the mass
spectra analysis of SOA formed in a Potential Aerosol Mass (PAM) chamber. PAM is defined as the maximum
aerosol mass that precursor gases can be oxidized to form particulate matter. The PAM chamber is a flow-
through photo-oxidation chamber with extremely high OH and ozone amounts that were controlled by varying
the UV light exposure and relative humidity. The oxidant levels in the PAM chamber were calibrated by direct
measurements. The extreme oxidizing environment with measured values of up to 10 ppmv of O3, 500
pptv of OH, and 5 ppbv of HO2 enabled fast oxidation of volatile organic compounds (VOCs) and
formation of SOA in a few minutes. The exposure to OH and O3 in the PAM chamber were equivalent to
exposures of a few days to weeks in the atmosphere.
The mass spectra of the SOA from the photo-oxidation of alpha-pinene, m-xylene and p-xylene in the PAM
chamber were measured with a High-Resolution Aerosol Mass Spectrometer (HR-AMS). The mass spectra
are used
to determine the level of oxidation (oxygen/carbon ratio) of the SOA as a function of the
initial precursor gas and the OH exposure (OH concentration multiplied by reaction time). The aerosol is
found to become increasingly oxidized at higher exposures, indicating the importance of ongoing
photochemical 'aging' reactions.
A31B-0080
Gas-phase Precursors to Anthropogenic SOA: Using the MCM to Probe Detailed Observations of Aromatic Photo-oxidation
The formation of photochemical ozone and particulate matter are major priorities in the determination of European air quality policies. Predictions of the future state of the atmosphere and the development of appropriate mitigation strategies rely on models, which necessarily incorporate chemistry. The Master Chemical Mechanism (MCM, http://mcm.leeds.ac.uk/MCM) is a near-explicit chemical mechanism originally conceived to model ozone formation in Europe but now also employed as a benchmark mechanism in a wide variety of applications where chemical detail is required. The MCM currently describes the detailed gas- phase tropospheric degradation of a 135 primary emitted volatile organic compounds (VOCs) leading to a mechanism containing ca. 5900 species and 13500 reactions. In order that the MCM continues to be a state-of-the-art resource for the atmospheric science community it resides under a constant regime of evaluation, development and improvement. Individual VOC photochemical mechanisms are evaluated using data obtained, under a variety of atmospheric conditions, from highly instrumented smog chambers. Smog chamber experiments are crucial, not only for mechanism evaluation, but also for mechanism development. Findings obtained from combined model and chamber studies can additionally provide key insight for guiding the directions of future laboratory experiments. Recently, the MCM was updated to MCMv3.1 in order to take into account recent advancements in the understanding of aromatic photo-oxidation, an important class of anthropogenic VOCs. As well as constituting precursors to secondary organic aerosol (SOA), aromatics generally have high photochemical ozone creation potentials (POCPs) and hence contribute significantly towards tropospheric ozone formation. In the work presented, a detailed gas-phase photochemical chamber box model, incorporating the MCMv3.1 degradation mechanism for 1,3,5-trimethylbenzene (TMB), has been used to simulate data measured during a series of chamber experiments carried out at the Paul Scherrer Institute Aerosol Chamber in order to evaluate the mechanism under a variety of VOC/NOx conditions. More specifically, the model was used in the interpretation of data recorded by the University of Leicester's Chemical Ionisation Reaction Time-of- Flight Mass Spectrometer (CIR-TOF-MS), a novel instrument used to provide comprehensive, high (mass and time) resolution measurements of the organic gaseous oxidation products formed from the TMB precursor. Additional supporting gas and aerosol measurements also enable us to explore the "missing link" between the gas and aerosol phases. Model-measurement comparisons have been used to gain an insight into the complex array of oxygenated products formed, including the peroxide bicyclic ring opening products (gamma-dicarbonyls and furanones) and the O2-bridged peroxide bicyclic ring retaining products (diol, ketone and nitrate). To our knowledge this is the first time these O2-bridged species have been identified in the gas-phase. The model was also used to give insights into which gas-phase species were participating in SOA formation, with the primary and secondary peroxide products, formed primarily under NOx-limiting conditions ([NO] approaches zero), identified as likely candidates.
A31B-0081
Oxidation of the PAH Coronene by Ozone and the Hydroxyl Radical
Polycyclic aromatic hydrocarbons (PAHs) are a class of organic pollutants, consisting of two or more fused benzene rings, emitted directly into the atmosphere primarily through incomplete combustion processes and known to have allergenic, mutagenic, and carcinogenic effects. In the atmosphere, smaller PAHs are found primarily in gas-phase, whereas three or four- member ring compounds are partitioned between gas and particulate matter, and compounds with greater than five-member rings mostly reside in the particle phase. The atmospheric fate of these heavier PAHs is governed by heterogeneous reactions between the surface bound PAHs and gas-phase atmospheric oxidants such as ozone, the hydroxyl radical, and nitrates, however, these heterogeneous chemical reactions are relatively poorly understood and studied. In the current study, reactivity of the seven-member ring PAH coronene to oxidation sources ozone and hydroxyl radical is examined. To probe the extent of chemical reaction, product formation, and change in surface morphology as a function of reaction, we examine coronene adsorbed onto various substrates, from both a surface and bulk perspective, with ambient pressure photoemission spectroscopy (APPES) and aerosol mass spectrometry (AMS), respectively. In bulk on-line analysis, a 20nm thick layer of coronene adsorbed onto NaCl seed particles and reacted with either oxidant in a flow tube showed very little reactant conversion to product in the AMS. However, surface analysis by the APPES of the same reaction where coronene was adsorbed onto model substrates showed up to 90% conversion of the carbon species to volatilized or oxidized carbon. Data obtained with these two complimentary bulk and surface techniques provide evidence for a surface selective reaction. Using APPES, we are able observe the two oxidation reactions transforming on different timescales and through differing pathways, resulting in dissimilar final states.
A31B-0082
Branching between fragmentation and functionalization pathways in the oxidation of atmospheric organics
Oxidation reactions that affect the volatility of organics are of central importance to the chemistry of the troposphere, as they lead to the formation of secondary organic aerosol, and can change the properties or loadings of existing particulate matter via oxidative processing ("aging"). Atmospheric oxidation can decrease the vapor pressure of an organic compound by adding oxygen-containing functional groups (increasing its polarity), or increase vapor pressure by breaking carbon-carbon bonds (decreasing its molecular weight). Despite being a fundamental determinant of the changes to volatilities of atmospheric organics, the functionalization/fragmentation branching ratio is not well-constrained for large atmospheric organics, especially for highly oxidized ones. Here we present laboratory measurements of this branching ratio for the heterogeneous oxidation of particulate organics. Particles of pure squalane (a branched C30 alkane) are sent into a flow reactor and are rapidly oxidized by exposure to high levels of OH; particle size and composition are measured as a function of OH exposure using a scanning mobility particle sizer (SMPS) and high-resolution time-of-flight aerosol mass spectrometer (AMS). Oxidation reactions are found to decrease particle mass, indicating volatilization (from carbon-carbon bond breaking) and also to increase the oxygen/carbon (O/C) ratio of the particulate organics, indicating the addition of functional groups. The relative rates of these two processes allows for the determination of the branching ratio between fragmentation and functionalization. Functionalization is found to dominate the oxidation of the pure hydrocarbon, but the importance of fragmentation increases as the organics become increasingly oxidized. Fragmentation pathways appear to dominate for organics with O/C ratios above ~30%.
A31B-0083
Investigations of ROx Radical Photochemistry During the MCMA-2006 Field Campaign
Measurements of hydroxyl (OH) and hydroperoxy (HO2) radicals were made during the Mexico City Metropolitan Area (MCMA) field campaign, providing an opportunity to investigate the strong coupling between ROX radicals (HOX = OH + HO2 + RO2), nitrogen oxides (NOX = NO + NO2) and Volatile Organic Compounds (VOCs). A highly constrained zero-dimensional box model, based on the Regional Atmospheric Chemical Mechanism (RACM), was used to investigate the daytime ROX chemistry. Several points are highlighted in this study: (i) Median concentrations of both OH and HO2 were underpredicted during morning hours, suggesting a significant source of radicals is missing from current atmospheric models under polluted conditions. (ii) The predicted HO2/OH ratios are underestimated for NO mixing ratios higher than 5 ppb, consistent with previous urban field campaigns, suggesting that under high NOX conditions, the propagation rate of HO2 to OH may be overestimated by the model, and/or a process converting OH into peroxy radicals is missing from the chemical mechanism. An investigation of the radical budget indicates that radical initiation in the MCMA is the result of several photolytic and non-photolytic processes. On a daily basis, O3-alkene reactions, photolysis of HONO, photolysis of HCHO and photolysis of dicarbonyls are the main source of radicals, while production of OH from O(1D) + H2O was found to be a small radical source for MCMA-2006. In addition, OH production from excited NO2 chemistry was found to be negligible compared to other sources.
A31B-0084
Initial Composition, Transformations, and Transport of Particles and Trace Gases From Mexican Biomass Burning
As part of the MILAGRO project we investigated the amount, transport, and chemical composition of emissions from biomass burning (BB) in Mexico. Up to 48 trace gas and particle species were measured. BB near Mexico City (MC) and in the Yucatan was sampled from the NCAR C-130 in March 2006. During the same month, a Twin Otter aircraft deployed by the University of Montana was used to sample fires in the above areas and also forest, grass, and agricultural fires throughout much of the rest of Mexico. BB adjacent to MC accounted for about 30% of the CO and half or more of the fine particle mass in the MC-area outflow. The Yucatan measurements now provide the most comprehensive data available on the emissions from BB in tropical dry forests: the ecosystem that accounts for the most biomass burned globally. Rapid changes in ozone and many other trace gas species were observed in one BB plume. The Δ PM2.5/Δ CO ratio increased by a factor of ~ 2.6 in < 2 hours after emission as measured by both light scattering and an aerosol mass spectrometer. This is the best field evidence to date of significant secondary aerosol formation in BB plumes. During April-May 2007, ground-based, portable FTIR and particle measuring systems were deployed throughout central Mexico to characterize the emissions from garbage burning, cooking fires, brick-making kilns, and other ubiquitous, but poorly characterized sources. The first detailed chemical speciation of garbage burning emissions included the observation of extremely high HCl levels (Δ HCl/Δ CO 3.5-18%). Thus, garbage burning could be an important source of atmospheric chlorine in some regions. In addition, the HCl results suggest that large amounts of other chlorinated compounds may be emitted. Further measurements are needed, especially for highly toxic chlorinated organic compounds. Cooking fires are the second largest global source of BB emissions. The measurements of trace gas and particle emissions from cooking fires included particulate organic and elemental carbon by filter sampling. Many residents of rural Mexican communities are routinely exposed to sustained, unhealthy levels of particulate pollution (PM2.5 ~ 1 mg/m3) during cooking operations. The newly available chemical speciation for the sources sampled in the ground-based campaign could significantly improve emissions inventories for much of the developing world.
A31B-0085
Unraveling Contributions of Urban, Biomass Burning and Secondary Organic Aerosols Near Mexico City During MILAGRO 2006
Organic aerosols (OA) can be classified into three broad categories: 1) primary organic aerosols (POA) directly emitted from urban sources (e.g., vehicular exhaust), 2) biomass burning organic aerosols (BBOA) directly emitted from forest/vegetation fires, and 3) secondary organic aerosols (SOA) from gas-to-particle conversion of semi-volatile and non-volatile organic species formed as a result of photooxidation of volatile organic compounds (VOCs) of both anthropogenic and biogenic origins. It is of great interest for both air quality and climate forcing purposes to quantify the contributions of these three types to the total OA mass observed at any given location. The Aerodyne Aerosol Mass Spectrometer (AMS) is particularly useful for obtaining high time-resolution measurements of OA mass concentrations. However, the difficulty lies in separating the POA, BBOA, and SOA fractions from the observed total OA mass. In this paper we focus on the analysis of the 10-min average AMS and PTR-MS data at the T1 ground site (just outside of Mexico City to the north) to unravel the contributions of the three OA fractions. We make use of acetylene (C2H2) and acetonitrile (CH3CN) mixing ratios as tracers of urban and biomass burning emissions, respectively, to first determine the POA and BBOA masses with the rather straightforward multi-linear regression (MLR) technique. SOA is then estimated from the difference between the total OA and POA+BBOA masses. A similar multi-linear regression analysis is also performed on the CO data to determine the urban and biomass burning components. We also apply the more sophisticated Positive Matrix Factorization (PMF) technique to deconvolve the AMS mass spectra into hydrocarbon-like organic aerosol (HOA), biomass burning-like organic aerosol (BBOA), and oxygenated organic aerosol (OOA). A comparison of the estimates of POA, BBOA, and SOA from the MLR and PMF analyses will be presented. The Δ[POA]/Δ[CO]urban and Δ[BBOA]/Δ[CO]fire ratios estimated from both the techniques will also be compared with those obtained from the available emissions inventory for the Mexico City area as well as with the available values in literature. Implications of our findings on POA and BBOA emission factors will be discussed.
A31B-0086
Understanding the Evolution of Organic Aerosols in the Mexico City Airshed in 2002, 2003 and 2006 using Positive Matrix Factorization
Aerosol mass spectrometric measurements yield spectra of ambient aerosols that are a mix of various primary and secondary sources. Organic aerosol (OA) datasets acquired using Aerodyne aerosol mass spectrometers (Q-AMS, C-ToF-AMS, and HR-ToF-AMS) deployed in 2002, 2003, and 2006 in the Mexico City Metropolitan Area (MCMA) at multiple ground locations and from aircraft flights are analyzed with Positive Matrix Factorization to deconvolve information about important sources and processes for organic aerosols. Several components are identified in each dataset. Most datasets resolve contributions from: reduced (oxidative state) hydrocarbon-like OA (HOA), which correlates well with primary combustion tracers such as CO, NOx, and BC; biomass burning OA (BBOA), which correlates with regional fire counts, potassium, levoglucosan, acetonitrile, and HCN; highly-oxidized OA (OOA-I) which shows more regional behavior; and less oxidized OA (OOA-II) which correlates with semivolatile inorganic species such as ammonium nitrate and gas-phase secondary species such as Ox (NO2 + O3) and glyoxal. These correlations are consistent across most datasets when run separately in PMF. Factor spectra are also compared to reference spectra, and ratios of factor concentrations to relevant tracers (e.g., HOA/CO, OOA/Ox) are presented. Factor spectra, time series, diurnal cycles, and ratios are compared at sampling locations across the MCMA and in different years in order to understand the evolution of OA across the airshed. The effect of running multiple datasets within a single PMF model (e.g., simultaneous measurements made at two locations in Mexico City), and the stability of PMF solutions will be described.
A31B-0087
Organic Aerosols in New York City -- Insights into Sources, Processes, and Seasonal Variations Based on Aerosol Mass Spectrometry
Size-resolved organic aerosol (OA) chemistry was characterized in New York City during summer 2001 and winter 2004 with an Aerodyne Quadrupole Aerosol Mass Spectrometer (Q-AMS), as part of the PM2.5 Technology Assessment and Characterization Study – New York (PMTACS-NY). The AMS OA data were analyzed with multivariate statistical techniques, including Multiple Component Analysis (MCA) and Positive Matrix Factorization (PMF), to deconvolve and determine the time series, mass spectra, and size distributions of multiple OA components. The hydrocarbon-like organic aerosol (HOA) components extracted separately for the summer and winter datasets showed close similarity in mass spectra and size distributions. The oxygenated organic aerosol (OOA) components, however, showed more seasonal variations and were overall more oxidized in summer than in winter. Although the HOA concentration was on average higher in winter than in summer, the average OOA concentration was significantly lower, indicating much more intensified production of secondary OA in summer. The average mass concentration of total OA was approximately 20 percent higher in summer than in winter. In order to understand the sources and atmospheric processes of OA in New York City, we examined the correlations of OA components with various gas phase and particulate tracer compounds as well as their diurnal variation patterns and the time-resolved size distributions. In addition, the results of back trajectory analysis with HYSPLIT will also be included for discussions on the source regions and possible transportation pathways of submicron OA particles observed in New York City.
A31B-0088
Size-Resolved Volatility and Chemical Composition of Aged European Aerosol Measured During FAME-2008
We present first results on the volatility and chemical composition of aged organic aerosol measured during the Finokalia Aerosol Measurement Experiment – 2008 (FAME-2008). Finokalia is located in the Southeast of Crete, Greece, and this remote site allows for the measurement of aged European aerosol as it is transported from Central to Southeastern Europe. We measured the volatility of the aerosol at Finokalia as a function of its size by combining several instruments. We used an Aerodyne quadrupole aerosol mass spectrometer (Q-AMS) to measure the size-resolved chemical composition of the particles, a scanning mobility particle sizer (SMPS) to measure the volume distribution of particles, and a thermodenuder system to induce changes in size and composition via moderate heating of the particles. The largest fraction of the non-refractory material in the aerosol sampled was ammonium sulfate and ammonium bisulfate, followed by organic material and a small contribution from nitrate. Most of the organic aerosol was highly oxidized, even after only a few days of transport over continental Europe. These highly oxidized organics had lower volatility than fresh primary or secondary aerosol measured in the laboratory. Significant changes in air-parcel trajectories and wind direction led to changes in the chemical composition of the sampled aerosol and corresponding changes of the volatility. These results allow the quantification of the effect of atmospheric processing on organic aerosol volatility and can be used as constraints for atmospheric Chemical Transport Models that predict the aerosol volatility.
A31B-0089
Measurement of Glyoxal Using an Incoherent Broadband Cavity Enhanced Absorption Spectrometer
Glyoxal (CHOCHO) is the simplest alpha-dicarbonyl and one of the most prevalent dicarbonyls in the atmosphere. It is formed from the photooxidation of anthropogenic hydrocarbons (e.g. aromatics and acetylene), and is a minor oxidation product of isoprene and other biogenic species. Photolysis of glyoxal is a significant source of HOx (OH + HO2), and there is growing evidence that heterogeneous reactions of glyoxal play an important role in the formation of secondary organic aerosol. We present a novel technique for measurement of glyoxal using cavity enhanced absorption spectroscopy with a broadband light source (IBBCEAS). The output of a Xenon arc lamp is coupled into a 1 m optical cavity, and the spectrum of light exiting the cavity is recorded by a grating spectrometer with a charge- coupled device (CCD) array detector. The mirror reflectivity and effective path lengths are determined from the known Rayleigh scattering of He and dry zero air (N2 + O2). We use least-squares fitting with published reference spectra to simultaneous retrieve glyoxal, nitrogen dioxide (NO2), oxygen dimer (O4) and water (H2O) in the 441 to 469 nm spectral range. For a 1-min sampling time, the precision (±1σ) on signal for measurements of CHOCHO and NO2 is 29 pptv and 20 pptv respectively. We directly compare the incoherent broadband cavity enhanced absorption spectrometer to 404 and 532 nm cavity ringdown instruments for CHOCHO and NO2 detection, and find linear agreement over a wide range of concentrations. We present laboratory measurements of synthetic and real air samples containing CHOCHO and NO2, and discuss the potential for field measurements.
A31B-0090
Aerosol-Forming Reactions of Glyoxal, Methylglyoxal and Amino Acids in Clouds
Glyoxal and methylglyoxal are two common aldehydes present in fog and cloud water. Amino acids are present in clouds at similar concentrations. Here we present bulk and aerosol mass spectroscopic data demonstrating that irreversible reactions between glyoxal and amino acids, triggered by droplet evaporation, produce N-derivatized imidazole compounds along with deeply colored Maillard reaction products. These reactions can occur in the dark and in the absence of oxidants. Reactions between methylglyoxal and amino acids produce analogous methylated products plus oligomers with masses up to m/z = 1000. These reactions, which go to completion on the 10-min-timescale of cloud processing, could be significant sources of secondary organic aerosol and humic-like substances (HULIS or brown carbon).
A31B-0091
Size distributions of low molecular weight dicarboxylic acids, ketocarboxylic acids, glyoxal and methylglyoxal in the marine aerosols from Okinawa Island, Japan
Size-segregated marine aerosol samples (5 sets) were collected in 2008 spring at Cape Hedo Station of National Institute of Environmental Studies, Okinawa (128.25° E, 26.87° N), an outflow region of Chinese aerosols and their precursors, using an Andersen middle volume impactor at a flow rate of 100 lpm and pre-combusted quartz fiber filters. The samples were analyzed for low molecular weight diacids and related compounds, using a capillary gas chromatography and GC/MS after BF3/n-butanol derivatization. Particle size cuts (8 stages + BUF) are 0.43, 0.65, 1.1, 2.1, 3.3, 4.7, 7 and 11.3 µm in diameter. Homologous series of aliphatic (C2-C12) and aromatic (phthalic, iso- and tere-phthalic) diacids were detected as well as w-oxoacids (C2-C9), glyoxal and methylglyoxal. Oxalic acid (C2) was found as the dominant diacid in all the size ranges, followed by malonic (C3) and succinic (C4) acids. Glyoxylic (wC2) acid was the most abundant ketoacid followed by wC4 acid. Most of the organic species maximized in fine mode of 0.65-1.1 or 1.1-2.1µm. Oxalic acid (C2, 4.4-70.6 ngm-3, av. 23.9 ngm-3) comprised 54-80% (av. 67%) of total diacid concentrations. The small diacids showed concentration peaks on fine mode, suggesting that they are produced by photochemical oxidation of volatile organic precursors during long-range atmospheric transport from Asian Continent. They may also be produced by heterogeneous reactions in the atmospheric particles (dusts and cloud droplets).
A31B-0092
Aerosol organic nitrate characterization and quantification with the High Resolution-Time of Flight-Aerosol Mass Spectrometer
Organic nitrates (RONO2) are the results of NOx-VOC-HOx chemistry and account for a significant fraction of reactive oxidized nitrogen in the troposphere, particularly in urban and sub-urban sites. Based on their physical properties, organic nitrates may comprise a significant fraction of secondary organic aerosol (SOA). However, few studies have investigated this possibility as instrumental limitations have hindered investigation into the extent to which complex organic nitrates partition between the gaseous and particulate phases. This partitioning affects not only our understanding of SOA chemistry, but also the lifetime of organic nitrates, the extent to which they act as sinks for NOx, and nitrogen deposition to ecosystems. High-resolution mass spectral characterization of particulate organic nitrate standards derived from reactions of anthropogenic precursors, namely oleic acid with NO3 radicals and 1-tetradecane with OH radicals in the presence of NOx, with a High Resolution-Time of Flight-Aersol Mass Spectrometer (HR-ToF-AMS; DeCarlo et al., Anal. Chem., 2006) in conjunction with a High Performance Liquid Chromatograph allow us to characterize the response of the HR-ToF-AMS to particulate organic nitrates. Several alternative methods for organic nitrate estimation from ambient data are developed based on the laboratory calibrations, and applied to recent datasets from megacities (Mexico City during MILAGRO and the Los Angeles area during SOAR-1) and rural environments such as Blodgett Forest.
A31B-0093
Characterization of Atmospheric Organic Nitrates in Particles
Aerosols in the atmosphere significantly affect climate, human health and visibility. Knowledge of aerosol composition is necessary to understand and then predict the specific impacts of aerosols in the atmosphere. It is known that organic nitrates are present in particles, but there is limited knowledge of the individual compounds and quantity. This is in part due to the lack of a wide variety of proven analytical techniques for particulate organic nitrates. In this study, several known organic nitrates, as well as those present in complex mixtures formed from oxidation of Ą-pinene, were studied using a variety of techniques. These include Fourier Transform infrared spectroscopy (FTIR) of samples collected by impaction on ZnSe discs. Samples were also collected on quartz fiber filters and the extracts analyzed by electrospray mass spectrometry (ESI- MS), atmospheric pressure chemical ionization mass spectrometry (APCI-MS), HPLC-UV, LC-MS and GC-MS. In addition, real-time analysis was provided by SPLAT-II and aerosol mass spectrometry (AMS). FTIR analysis of particles collected on ZnSe discs provides information on the ratio of organic nitrate to total organic content, while the analysis of filter extracts allows identification of specific organic nitrates. These are compared to the particle mass spectrometry data and the implications for detecting and measuring particulate organic nitrate in air is discussed.
A31B-0094
Measurement of Organic Nitrogen Budget in Atmospheric Aerosol
Organic nitrogen in atmospheric aerosol is little known due to lack of measurement techniques. In this study, we determined the amount of organic nitrogen by imposing a new technique at the Duke Forest Research Facility. At first, the aerosol sample was collected from the SJAC. Then, the amount of organic nitrogen was calculated by subtracting the inorganic nitrogen species (NO3-, NH4+ which was measured from the ICs) from the total nitrogen (measured by the TOC/TN unit) with a resolution time of 30min. We will also exam how organic nitrogen correlates with other measured aerosol components and its dependence on meteorological parameters. Along with observed seasonal and diurnal characteristics of organic nitrogen, the origin and properties of organic nitrogen in atmospheric aerosol will be further elucidated.
A31B-0095
Heterogeneous OH oxidation of organic aerosols
The hydroxyl radical (OH) is the most important reactive species in both clean and polluted atmospheres, and therefore gas-phase OH chemistry has been extensively studied for decades. Due to this enormous effort the rates and mechanism of OH reactions with gas phase organics are relatively well understood. However, it unclear whether these well established gas-phase chemical mechanisms apply to the more complex heterogeneous reactions of OH radicals with organic aerosols (OA). Although recent studies have begun to examine OH oxidation of OA, numerous outstanding questions still remain regarding both the rate and chemical mechanism of these reactions. Here we present an in depth investigation of the heterogeneous oxidation of organic squalane particles by OH radicals. By combining a photochemical aerosol flow reactor with a high-resolution aerosol mass spectrometer (AMS), with both electron impact and vacuum ultraviolet photoionization, we investigate OH heterogeneous chemistry in unprecedented detail. Employing elemental composition measurements with detailed kinetics we have arrived at a simple oxidation model which accurately accounts for the evolution of squalane and its" oxidation products. In addition, by exploring a large range of OH concentrations we are able to directly measure the role of secondary particle-phase chain chemistry which can significantly accelerate the oxidation of OA in the atmosphere. Based on these measurements we have arrived at an explicit chemical mechanism for heterogeneous OH oxidation of OA which accurately accounts for our observations over a wide range of reaction conditions.