Chemical Composition Of Organic Aerosol Research Articles

Chemical Characterization of Rural Organic Aerosol in the North China Plain Using Ultrahigh-Resolution Mass Spectrometry

Atmospheric organic aerosol (OA) affects air quality and human health. However, compared with urban areas, the chemical composition and temporal distribution of OA in rural regions are still not well understood. In this study, one-year atmospheric particles with an aerodynamic equivalent diameter of ≤2.5 μm (PM2.5) were collected at a rural site in Quzhou County, the North China Plain (NCP), from August 2020 to July 2021. OA in PM2.5 samples were analyzed with an ultrahigh-performance liquid chromatograph (UHPLC) coupled to an ultrahigh-resolution Orbitrap mass spectrometer in negative mode (ESI−). The results show that the chemical composition and properties of OA varied in different seasons. According to the hierarchical cluster analysis, the molecular formulas of winter OA were close to those in spring, whereas the chemical composition of OA in summer and autumn was similar. The O/C ratio of summer OA was the highest at 1.21, followed by that in autumn (0.92) and spring (0.87), while the winter OA had the lowest O/C ratio of 0.64. It indicates that, compared to the other three seasons, OA underwent more intense oxidation processes in the summer. Moreover, winter OA contained more aromatic compounds with a relative peak abundance fraction of 40%, which may be related to anthropogenic sources (e.g., coal burning) in the winter in the NCP. In addition, biomass burning is considered an important source of OA in the rural region of Quzhou County, the NCP, in all seasons.

Hybrid Targeted/Untargeted Screening Method for the Determination of Wildfire and Water-Soluble Organic Tracers in Ice Cores and Snow.

Wildfires can influence the earth's radiative forcing through the emission of biomass-burning aerosols. To better constrain the impacts of wildfires on climate and understand their evolution under future climate scenarios, reconstructing their chemical nature, assessing their past variability, and evaluating their influence on the atmospheric composition are essential. Ice cores are unique to perform such reconstructions representing archives not only of past biomass-burning events but also of concurrent climate and environmental changes. Here, we present a novel methodology for the quantification of five biomass-burning proxies (syringic acid, vanillic acid, vanillin, syringaldehyde, and p-hydroxybenzoic acid) and one biogenic emission proxy (pinic acid) using solid phase extraction (SPE) and ultrahigh-performance liquid chromatography coupled with high-resolution mass spectrometry. This method was also optimized for untargeted screening analysis to gain a broader knowledge about the chemical composition of organic aerosols in ice and snow samples. The method provides low detection limits (0.003-0.012 ng g-1), high recoveries (74 ± 10%), and excellent reproducibility, allowing the quantification of the six proxies and the identification of 313 different molecules, mainly constituted by carbon, hydrogen, and oxygen. The effectiveness of two different sample storage strategies, i.e., re-freezing of previously molten ice samples and freezing of previously loaded SPE cartridges, was also assessed, showing that the latter approach provides more reproducible results.

Diurnal variations in primary and secondary organic aerosols in an eastern China coastal city: The impact of land-sea breezes

The land-sea breeze circulation significantly impacts the atmospheric transport of organic aerosols in coastal regions. However, the links between organic aerosols and land-sea breezes remain poorly understood. In this study, organic marker compounds for biomass burning, primary biological aerosols, biogenic and anthropogenic secondary organic aerosols (SOA) in fine particles from a coastal city in East China were analysed using gas chromatography–mass spectrometry. Land-sea breeze circulations were identified to explore their potential influence on organic molecular compositions. Organic marker compounds showed obvious diurnal/seasonal patterns. Surprisingly, due to the combined influence of weakened East Asian monsoons and land-sea breezes, all detected organic markers decreased except α/β-pinene SOA markers during land-sea breeze periods in early autumn; whereas, all the organic markers increased except α/β-pinene SOA markers, pollen and plant debris markers during land-sea breeze periods in early spring. Furthermore, the reaction pathway and aging of biogenic SOA were also related to land-sea breezes. During the land-sea breeze periods, the ratios of 2-methylglyceric acid (2-MGA) to 2-methyltetrols increased in early autumn, indicating that more isoprene-derived SOA generated from the high-NOx (nitrogen oxides) pathway when the land-sea breezes occurred; while the ratios decreased in early spring, this may be related to the chemical transformation of 2-MGA to 2-MGA sulfates. Changes in the ratio of monoterpene SOA markers demonstrate that monoterpene SOA was relatively aged during sea breeze periods, while it was fresher when the land breeze occurred. Although boundary layer height, emissions, gas/particle partitioning, etc. are important reasons for the diurnal variations of organic aerosols, night/day ratios of molecular markers increased obviously when land-sea breezes occurred in both early autumn and early spring. Our results provide new insights into the shift in the chemical composition of organic aerosols over coastal areas that are influenced by land-sea breezes.

Regional heterogeneities in the emission of airborne primary sugar compounds and biogenic secondary organic aerosols in the East Asian outflow: evidence for coal combustion as a source of levoglucosan

Abstract. Biomass burning (BB) significantly influences the chemical composition of organic aerosols (OAs) in the East Asian outflow. The source apportionment of BB-derived OA is an influential factor for understanding their regional emissions, which is crucial for reducing uncertainties in their projected climate and health effects. We analyzed here three different classes of atmospheric sugar compounds (anhydrosugars, primary sugars, and sugar alcohols) and two types of biogenic secondary organic aerosol (BSOA) tracers (isoprene- and monoterpene-derived SOA products) from a year-long study that collected total suspended particulate matter (TSP) from an island-based receptor site in Gosan, South Korea. We investigate the seasonal variations in the source emissions of BB-derived OA using mass concentrations of anhydrosugars and radiocarbon (14C-) isotopic composition of organic carbon (OC) and elemental carbon (EC) in ambient aerosols. Levoglucosan (Lev) is the most abundant anhydrosugar, followed by galactosan (Gal), and mannosan (Man). Strong correlations of Lev with Gal and Man, along with their ratios (Lev/Gal is 6.65±2.26; Lev/Man is 15.1±6.76) indicate the contribution from hardwood burning emissions. The seasonal trends revealed that the BB impact is more pronounced in winter and fall, as evidenced by the high concentrations of anhydrosugars. Likewise, significant correlations among three primary sugars (i.e., glucose, fructose, and sucrose) emphasized the contribution of airborne pollen. The primary sugars showed higher concentrations in spring/summer than winter/fall. The fungal spore tracer compounds (i.e., arabitol, mannitol, and erythritol) correlated well with trehalose (i.e., a proxy for soil organic carbon), suggesting the origin from airborne fungal spores and soil microbes in the East Asian outflow. These sugar alcohols peaked in summer, followed by spring/fall and winter. Monoterpene-derived SOA tracers were most abundant compared to isoprene SOA tracers. Both BSOA tracers were dominant in summer, followed by fall, spring, and winter. The source apportionment based on multiple linear regressions and diagnostic mass ratios together revealed that BB emissions mostly contributed from hardwood and crop residue burning. We also found significant positive linear relationships of 14C-based nonfossil- and fossil-derived organic carbon fractions with Lev C, along with the comparable regression slopes, suggesting the importance of BB and coal combustion sources in the East Asian outflow.

Airborne extractive electrospray mass spectrometry measurements of the chemical composition of organic aerosol

Abstract. We deployed an extractive electrospray ionization time-of-flight mass spectrometer (EESI-MS) for airborne measurements of biomass burning aerosol during the Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) study onboard the NASA DC-8 research aircraft. Through optimization of the electrospray working solution, active control of the electrospray region pressure, and precise control of electrospray capillary position, we achieved 1 Hz quantitative measurements of aerosol nitrocatechol and levoglucosan concentrations up to pressure altitudes of 7 km. The EESI-MS response to levoglucosan and nitrocatechol was calibrated for each flight, with flight-to-flight calibration variability of 60 % (1σ). Laboratory measurements showed no aerosol size dependence in EESI-MS sensitivity below particle geometric diameters of 400 nm, covering 82 % of accumulation-mode aerosol mass during FIREX-AQ. We also present a first in-field intercomparison of EESI-MS with a chemical analysis of aerosol online proton-transfer-reaction mass spectrometer (CHARON PTR-MS) and a high-resolution Aerodyne aerosol mass spectrometer (AMS). EESI-MS and CHARON PTR-MS levoglucosan concentrations were well correlated, with a regression slope of 0.94 (R2=0.77). AMS levoglucosan-equivalent concentrations and EESI-MS levoglucosan showed a greater difference, with a regression slope of 1.36 (R2=0.96), likely indicating the contribution of other compounds to the AMS levoglucosan-equivalent measurement. The total EESI-MS signal showed correlation (R2=0.9) with total organic aerosol measured by AMS, and the EESI-MS bulk organic aerosol sensitivity was 60 % of the sensitivity to levoglucosan standards.

Chemical composition of waste burning organic aerosols at landfill and urban sites in Delhi

Organic composition of total suspended particles collected from an open waste burning landfill site and an urban site of Delhi, one of the most populated cities of Asia was studied. Among the organic compounds detected, fatty acids were found to be the most abundant class of compounds at both the sites, urban (16823 ng m−3) as well as landfill site (1218120 ng m−3). As a single compound detected (on average), levoglucosan (2925 ng m−3) was found to be most abundant at urban site, whereas C18:0 fatty acid (76090 ng m−3) dominated at the landfill site. Levoglucosan contributed up to 87% of total identified sugars at urban and 86% at landfill site, suggesting biomass burning to be one of the major contributors of sugar compounds, and a possible influence of landfill waste burning on urban aerosols. CPI value for n-alkanes was close to unity at both sites (0.81 at landfill and 1.27 at urban site) indicating the anthropogenic nature of the aerosols. A predominance of tere-phthalic acid (42555 ng m−3) was found in aerosol samples collected at landfill site because of plastic enriched waste burning activity. Except 4- hydroxybenzoic acid, all other lignin and resin products are first time reported to be released by open waste burning activities in the present study. We also found a strong positive correlation between di-isobutyl phthalate and di-n-butyl phthalate at both urban (r2 = 0.94) and landfill site (r2 = 0.86), suggesting them to be the commonly used plasticizers, and plastics to be a main constituent of municipal waste. Since, the waste burning at landfill sites is a common practice either to reduce waste heaps or be it a self-ignited burning leading to significant emissions, we report the chemical composition of organic aerosols originating from such emissions. The information presented in this paper may further be useful in estimating the contribution of municipal waste burning aerosols on urban burden of particulate matter.

Infrared Ion Spectroscopy of Environmental Organic Mixtures: Probing the Composition of α-Pinene Secondary Organic Aerosol.

Characterizing the chemical composition of organic aerosols can elucidate aging mechanisms as well as the chemical and physical properties of the aerosol. However, the high chemical complexity and often low atmospheric abundance present a difficult analytical challenge. Milligrams or more of material may be needed for speciated spectroscopic analysis. In contrast, mass spectrometry provides a very sensitive platform but limited structural information. Here, we combine the strengths of mass spectrometry and infrared (IR) action spectroscopy to generate characteristic IR spectra of individual, mass-isolated ion populations. Soft ionization combined with in situ infrared ion spectroscopy, using the tunable free-electron laser FELIX, provides detailed information on molecular structures and functional groups. We apply this technique, along with quantum mechanical modeling, to characterize organic molecules in secondary organic aerosol (SOA) formed from the ozonolysis of α-pinene. Spectral overlap with a standard is used to identify cis-pinonic acid. We also demonstrate the characterization of isomers for multiple SOA products using both quantum mechanical computations and analyses of fragment ion spectra. These results demonstrate the detailed structural information on isolated ions obtained by combining mass spectrometry with fingerprint IR spectroscopy.

Multiphase composition changes and reactive oxygen species formation during limonene oxidation in the new Cambridge Atmospheric Simulation Chamber (CASC)

Abstract. The chemical composition of organic aerosols influences their impacts on human health and the climate system. Aerosol formation from gas-to-particle conversion and in-particle reaction was studied for the oxidation of limonene in a new facility, the Cambridge Atmospheric Simulation Chamber (CASC). Health-relevant oxidising organic species produced during secondary organic aerosol (SOA) formation were quantified in real time using an Online Particle-bound Reactive Oxygen Species Instrument (OPROSI). Two categories of reactive oxygen species (ROS) were identified based on time series analysis: a short-lived component produced during precursor ozonolysis with a lifetime of the order of minutes, and a stable component that was long-lived on the experiment timescale (∼ 4 h). Individual organic species were monitored continuously over this time using Extractive Electrospray Ionisation (EESI) Mass Spectrometry (MS) for the particle phase and Proton Transfer Reaction (PTR) MS for the gas phase. Many first-generation oxidation products are unsaturated, and we observed multiphase aging via further ozonolysis reactions. Volatile products such as C9H14O (limonaketone) and C10H16O2 (limonaldehyde) were observed in the gas phase early in the experiment, before reacting again with ozone. Loss of C10H16O4 (7-hydroxy limononic acid) from the particle phase was surprisingly slow. A combination of reduced C = C reactivity and viscous particle formation (relative to other SOA systems) may explain this, and both scenarios were tested in the Pretty Good Aerosol Model (PG-AM). A range of characterisation measurements were also carried out to benchmark the chamber against existing facilities. This work demonstrates the utility of CASC, particularly for understanding the reactivity and health-relevant properties of organic aerosols using novel, highly time-resolved techniques.

Comprehensive modeling study of ozonolysis of oleic acid aerosol based on real‐time, online measurements of aerosol composition

AbstractThe chemical composition of organic aerosols profoundly influences their atmospheric properties, but a detailed understanding of heterogeneous and in‐particle reactivity is lacking. We present here a combined experimental and modeling study of the ozonolysis of oleic acid particles. An online mass spectrometry (MS) method, Extractive Electrospray Ionization (EESI), is used to follow the composition of the aerosol at a molecular level in real time; relative changes in the concentrations of both reactants and products are determined during aerosol aging. The results show evidence for multiple non‐first‐order reactions involving stabilized Criegee intermediates, including the formation of secondary ozonides and other oligomers. Offline liquid chromatography MS is used to confirm the online MS assignment of the monomeric and dimeric products. We explain the observed EESI‐MS chemical composition changes, and chemical and physical data from previous studies, using a process‐based aerosol chemistry simulation, the Pretty Good Aerosol Model (PG‐AM). In particular, we extend previous studies of reactant loss by demonstrating success in reproducing the time dependence of product formation and the evolving particle size. This advance requires a comprehensive chemical scheme coupled to the partitioning of semivolatile products; relevant reaction and evaporation parameters have been refined using our new measurements in combination with PG‐AM.

Heterogeneous Oxidation of Atmospheric Organic Aerosol: Kinetics of Changes to the Amount and Oxidation State of Particle-Phase Organic Carbon.

Atmospheric oxidation reactions are known to affect the chemical composition of organic aerosol (OA) particles over timescales of several days, but the details of such oxidative aging reactions are poorly understood. In this study we examine the rates and products of a key class of aging reaction, the heterogeneous oxidation of particle-phase organic species by the gas-phase hydroxyl radical (OH). We compile and reanalyze a number of previous studies from our laboratories involving the oxidation of single-component organic particles. All kinetic and product data are described on a common basis, enabling a straightforward comparison among different chemical systems and experimental conditions. Oxidation chemistry is described in terms of changes to key ensemble properties of the OA, rather than to its detailed molecular composition, focusing on two quantities in particular, the amount and the oxidation state of the particle-phase carbon. Heterogeneous oxidation increases the oxidation state of particulate carbon, with the rate of increase determined by the detailed chemical mechanism. At the same time, the amount of particle-phase carbon decreases with oxidation, due to fragmentation (C-C scission) reactions that form small, volatile products that escape to the gas phase. In contrast to the oxidation state increase, the rate of carbon loss is nearly uniform among most systems studied. Extrapolation of these results to atmospheric conditions indicates that heterogeneous oxidation can have a substantial effect on the amount and composition of atmospheric OA over timescales of several days, a prediction that is broadly in line with available measurements of OA evolution over such long timescales. In particular, 3-13% of particle-phase carbon is lost to the gas phase after one week of heterogeneous oxidation. Our results indicate that oxidative aging represents an important sink for particulate organic carbon, and more generally that fragmentation reactions play a major role in the lifecycle of atmospheric OA.

A molecular-level approach for characterizing water-insoluble components of ambient organic aerosol particulates using ultrahigh-resolution mass spectrometry

Abstract. The chemical composition of organic aerosols in the atmosphere is strongly influenced by human emissions. The effect these have on the environment, human health, and climate change is determined by the molecular nature of these chemical species. The complexity of organic aerosol samples limits the ability to study the chemical composition, and therefore the associated properties and the impacts they have. Many studies have addressed the water-soluble fraction of organic aerosols and have had much success in identifying specific molecular formulas for thousands of compounds present. However, little attention is given to the water-insoluble portion, which can contain most of the fossil material that is emitted through human activity. Here we compare the organic aerosols present in water extracts and organic solvent extracts (pyridine and acetonitrile) of an ambient aerosol sample collected in a rural location that is impacted by natural and anthropogenic emission sources. A semiquantitative method was developed using proton nuclear magnetic resonance spectroscopy to determine that the amount of organic matter extracted by pyridine is comparable to that of water. Electrospray ionization Fourier transform ion cyclotron resonance mass spectra show that pyridine extracts a molecularly unique fraction of organic matter compared to water or acetonitrile, which extract chemically similar organic matter components. The molecular formulas unique to pyridine were less polar, more aliphatic, and reveal formulas containing sulfur to be an important component of insoluble aerosol organic matter.

Characterizing an Extractive Electrospray Ionization (EESI) Source for the Online Mass Spectrometry Analysis of Organic Aerosols

Organic compounds comprise a major fraction of tropospheric aerosol and understanding their chemical complexity is a key factor for determining their climate and health effects. We present and characterize here a new online technique for measuring the detailed chemical composition of organic aerosols, namely extractive electrospray ionization mass spectrometry (EESI-MS). Aerosol particles composed of soluble organic compounds were extracted into and ionized by a solvent electrospray, producing molecular ions from the aerosol with minimal fragmentation. We demonstrate here that the technique has a time resolution of seconds and is capable of making stable measurements over several hours. The ion signal in the MS was linearly correlated with the mass of aerosol delivered to the EESI source over the range tested (3-600 μg/m(3)) and was independent of particle size and liquid water content, suggesting that the entire particle bulk is extracted for analysis. Tandem MS measurements enabled detection of known analytes in the sub-μg/m(3) range. Proof-of-principle measurements of the ozonolysis of oleic acid aerosol (20 μg/m(3)) revealed the formation of a variety of oxidation products in good agreement with previous offline studies. This demonstrates the technique's potential for studying the product-resolved kinetics of aerosol-phase chemistry at a molecular level with high sensitivity and time resolution.

THE INFLUENCE OF BENZENE AS A TRACE REACTANT IN TITAN AEROSOL ANALOGS

Benzene has been detected in Titan's atmosphere by Cassini instruments, with concentrations ranging from sub-ppb in the stratosphere to ppm in the ionosphere. Sustained levels of benzene in the haze formation region could signify that it is an important reactant in the formation of Titan's organic aerosol. To date, there have not been laboratory investigations to assess the influence of benzene on aerosol properties. We report a laboratory study on the chemical composition of organic aerosol formed from C6H6/CH4/N2 via far ultraviolet irradiation (120-200 nm). The compositional results are compared to those from aerosol generated by a more traditional Titan mixture of CH4/N2. Our results show that even a trace amount of C6H6 (10 ppm) has significant impact on the chemical composition and production rates of organic aerosol. There are several pathways by which photolyzed benzene may react to form larger molecules, both with and without the presence of CH4, but many of these reaction mechanisms are only beginning to be explored for the conditions at Titan. Continued work investigating the influence of benzene in aerosol growth will advance understanding of this previously unstudied reaction system.

Molecular characterization of marine organic aerosols collected during a round-the-world cruise

[1] Organic molecular compositions of marine aerosol samples, collected at low latitudes to midlatitudes in the Northern Hemisphere during a round-the-world cruise, were studied using gas chromatography/mass spectrometry. More than 140 organic species were detected in the samples and were grouped into different compound classes based on the functionality and sources. The concentrations of total quantified organics ranged from 0.94 to 111 ng m−3 (average of 34 ng m−3). Biogenic secondary organic aerosol (SOA) tracers from the oxidation of isoprene (e.g., 2-methyltetrols), α/β-pinene (e.g., pinonic and pinic acids), and β-caryophyllene (β-caryophyllinic acid) were detected in all the samples. Their total concentrations ranged from 0.19 to 27 ng m−3, which account for 0.48–29% of the total identified organics and 0.05–1.5% of organic carbon in the marine aerosols. The spatial distributions of biogenic SOA tracers exhibited higher loadings over the coastal/tropical regions than the open oceans. In marine aerosols collected over the North Pacific and North Atlantic, the contributions of marine natural emissions (22–33%) were higher than those in the coastal regions (4–14%). Over the tropical regions, atmospheric oxidation products can account for 47–59% of the total organics, with biomass burning emissions of only 1–2%. However, over the western North Pacific, fossil fuel combustion (26%), atmospheric oxidation products (25%), and biomass burning (24%) were the main sources. This study indicates that long-range atmospheric transport of continental aerosols and sea-to-air emission of marine organics, as well as atmospheric oxidation and/or photochemical aging, are important factors controlling the chemical composition of organic aerosols in the marine atmosphere.

Analysis of the chemical composition of organic aerosol at the Mt. Sonnblick observatory using a novel high mass resolution thermal-desorption proton-transfer-reaction mass-spectrometer (hr-TD-PTR-MS)

Abstract. For the first time a high mass resolution thermal desorption proton transfer reaction mass spectrometer (hr-TD-PTR-MS) was deployed in the field to analyze the composition of the organic fraction of aerosols. We report on measurements from the remote Mt. Sonnblick observatory in the Austrian alps (3108 m a.s.l.) during a 7 week period in summer 2009. A total of 638 mass peaks in the range 18–392 Da were detected and quantified in aerosols. An empirical formula was tentatively attributed to 464 of these compounds by custom-made data analysis routines which consider compounds containing C, H, O, N, and S atoms. Most of the other (unidentified) compounds must contain other elements – most likely halogenated compounds. The mean total concentration of all detected compounds was 1.1 μg m−3. Oxygenated hydrocarbons constitute the bulk of the aerosol mass (75%) followed by organic nitrogen compounds (9%), inorganic compounds (mostly NH3, 8%), unidentified/halogenated (3.8%), hydrocarbons (2.7%), and organic sulfur compounds (0.8%). The measured O/C ratios are lower than expected and suggest a significant effect from charring. Organic carbon concentrations measured with TD-PTR-MS were about 25% lower than measurements on high volume filter samples.

Identification of secondary organic aerosol based on aerosol mass spectrometry

Secondary organic aerosol (SOA) is one of the major components of aerosols in the atmosphere and has not been well understood so far. Due to the complex chemical composition of organic aerosols, the identification of SOA has been a hotspot and difficult issue in the field of aerosol study. This study attempts to quantitatively identify SOA in winter, Shenzhen based on positive matrix factorization (PMF) analysis. Major sources were resolved and SOA were identified subsequently according to the characteristic ion fragments measured by highly time-resolved Aerosol Mass Spectrometer measurement. It showed that in the winter of Shenzhen the average SOA concentration was 9.41±6.33 μg/m3, accounting for 39.9±21.8% of the total organic mass. Compared with primary organic aerosol (POA), the SOA concentrations had no large variation, suggestive of characteristics of regional secondary pollutants. The ratio of SOA/BC had pronounced diurnal variation, similar to that of Ox (O3 + NO2), indicating SOA formation was significantly controlled by activity of photochemistry in the atmosphere. The most effective period for SOA formation was from 9 am–3 pm since the SOA/BC ratio increased by 122% during this period. This study provides a new technical method and a new idea for SOA investigation.

Identification of secondary organic aerosols based on aerosol mass spectrometry

Secondary organic aerosol (SOA) is one of the major components of aerosols in the atmosphere and has not been well understood so far. Due to the complex chemical composition of organic aerosols, the identification of SOA has been a hotspot and difficult issue in the field of aerosol study. This study attempts to quantitatively identify SOA in winter of Shenzhen based on positive matrix factorization (PMF) analysis. Major sources were resolved and SOA was identified subsequently according to the characteristic ion fragments measured by highly time-resolved aerosol mass spectrometer measurement. It showed that in the winter of Shenzhen the average SOA concentration was 9.41 ± 6.33 μg/m3, accounting for 39.9 ± 21.8% of the total organic mass. Compared with primary organic aerosol (POA), the SOA concentrations had no large variation, suggestive of characteristics of regional secondary pollutants. The ratio of SOA/BC had pronounced diurnal variation, similar to that of O x (O3+NO2), indicating SOA formation was significantly controlled by activity of photochemistry in the atmosphere. The most effective period for SOA formation was from 9 am ∼3 pm since the SOA/BC ratio increased by 122% during this period. This study provides a new technical method and a new idea for SOA investigation.

Aerosol analysis using a Thermal-Desorption Proton-Transfer-Reaction Mass Spectrometer (TD-PTR-MS): a new approach to study processing of organic aerosols

Abstract. We present a novel analytical approach to measure the chemical composition of organic aerosol. The new instrument combines proton-transfer-reaction mass-spectrometry (PTR-MS) with a collection-thermal-desorption aerosol sampling technique. For secondary organic aerosol produced from the reaction of ozone with isoprenoids in a laboratory reactor, the TD-PTR-MS instrument detected typically 80% of the mass that was measured with a scanning mobility particle sizer (SMPS). The first field deployment of the instrument was the EUCAARI-IOP campaign at the CESAR tall tower site in the Netherlands. For masses with low background values (~30% of all masses) the detection limit of aerosol compounds was below 0.2 ng/m3 which corresponds to a sampled compound mass of 35 pg. Comparison of thermograms from ambient samples and from chamber-derived secondary organic aerosol shows that, in general, organic compounds from ambient aerosol samples desorb at much higher temperatures than chamber samples. This suggests that chamber aerosol is not a good surrogate for ambient aerosol and therefore caution is advised when extrapolating results from chamber experiments to ambient conditions.

Photochemical and Other Sources of Organic Compounds in the Canadian High Arctic Aerosol Pollution during Winter−Spring

Total suspended particles collected at Alert in the Canadian high Arctic (February-June) were analyzed for solvent extractable organic compounds using gas chromatography-mass spectrometry to better understand the sources and source apportionment of aerosol pollution that can affect the Arctic climate. More than 100 organic species were detected in the aerosols and were grouped into different compound classes based on the functional groups. Polyacids were found to be the most abundant compound class, followed by phthalates, aromatic acids, fatty acids, fatty alcohols, sugars/sugar alcohols, and n-alkanes, while polycyclic aromatic hydrocarbons, sterols, and lignin and resin acids were minor. Concentrations of total quantified organics seemed slightly higher in darkwinter aerosols (13.2-16.6 ng m(-3), average 14.5 ng m(-3)) than those after polar sunrise (6.70-17.7 ng m(-3), average 11.8 ng m(-3)). During dark winter, fossil fuel combustion products (30-51%), secondary oxidation products, as well as higher plant emissions were found as major contributors to the Arctic aerosols. However, after polar sunrise on 5 March, secondary oxidation products (5-53%) and plasticizer-derived phthalates became the dominant compound classes, followed by fossil fuel combustion and microbial/marine sources. Biomass burning emissions were found to contribute only 0.4-6% of the total identified organics, although they maximized in dark winter. This study demonstrates that long-range atmospheric transport, changes in the solar irradiance, and ambient temperature can significantly control the chemical composition of organic aerosols in the Arctic region.

NMR Determination of Total Carbonyls and Carboxyls: A Tool for Tracing the Evolution of Atmospheric Oxidized Organic Aerosols

Nuclear magnetic resonance (NMR) spectroscopy is used to investigate the chemical composition of organic aerosol in terms of functional group distribution with a special focus on secondary organic aerosol (SOA) formation. The knowledge of the functional group composition is a benchmark for understanding how SOA components partition into the particulate phase and undergo chemical transformation. The paper presents a new chemical derivatization procedure coupled to proton NMR (1H NMR) analysis for the specific determination of total carbonylic groups in atmospheric aerosol samples, which couples with the procedure for determination of total carboxylic acid groups described in a previous work. A first deployment of the combined techniques for the analysis of PM10 samples collected in the Po Valley in the warm season shows that the concentration in the particulate phase of total carbonyls varies and covaries with respect to those of carboxylic acids and of less-oxidized functional groups. The proposed methodology provides the breakdown of the oxygenated fraction of the organic aerosol into major functional groups through well-established chemical methods and can be used to benchmark the more sensitive and widely used aerosol mass spectrometric techniques.