[1] Despite growing interest in the visible light-absorbing organic component of atmospheric aerosols, referred to as "brown" carbon, our knowledge of its chemical composition remains limited. It is well accepted that biomass burning is one important source of "brown" carbon in the atmosphere. In this study, cloud water samples heavily affected by biomass burning were collected at Mount Tai (1534 m, ASL), located in Shandong province in the North China Plain in summer 2008. The samples were analyzed with high performance liquid chromatography equipped with a UV/Vis absorbance detector immediately followed by electrospray ionization and analysis using a time-of-flight (ToF) mass spectrometer. The high mass resolution and accuracy provided by the ToF mass spectrometer allow determination of the elemental composition of detected ions. Using this approach, the elemental compositions of 16 major light-absorbing compounds, which together accounted for approximately half of measured sample absorption between 300 and 400 nm, were determined. The most important classes of light-absorbing compounds were found to be nitrophenols and aromatic carbonyls. Light absorption over this wavelength range by reduced nitrogen compounds was insignificant in these samples.

Chemical composition of secondary organic aerosol (SOA) formed from the ozone-initiated oxidation of limonene is characterized by high-resolution electrospray ionization mass spectrometry in both positive and negative ion modes. The mass spectra reveal a large number of both monomeric (m/z < 300) and oligomeric (m/z > 300) condensed products of oxidation. A combination of high resolving power (m/Deltam approximately 60,000) and Kendrick mass defect analysis makes it possible to unambiguously determine the molecular composition of hundreds of individual compounds in SOA samples. Van Krevelen analysis shows that the SOA compounds are heavily oxidized, with average O : C ratios of 0.43 and 0.50 determined from the positive and negative ion mode spectra, respectively. A possible reaction mechanism for the formation of the first generation SOA molecular components is considered. The discussed mechanism includes known isomerization and addition reactions of the carbonyl oxide intermediates generated during the ozonation of limonene. In addition, it includes isomerization and decomposition pathways for alkoxy radicals resulting from unimolecular decomposition of carbonyl oxides that have been disregarded by previous studies. The isomerization reactions yield numerous products with a progressively increasing number of alcohol and carbonyl groups, whereas C-C bond scission reactions in alkoxy radicals shorten the carbon chain. Together these reactions yield a large number of isomeric products with broadly distributed masses. A qualitative agreement is found between the number and degree of oxidation of the predicted and measured reaction products in the monomer product range.

[1] Detailed chemical speciation of the dry residue particles from individual cloud droplets and interstitial aerosol collected during the Marine Stratus Experiment (MASE) was performed using a combination of complementary microanalysis techniques. Techniques include computer controlled scanning electron microscopy with energy dispersed analysis of X rays (CCSEM/EDX), time-of-flight secondary ionization mass spectrometry (TOF-SIMS), and scanning transmission X-ray microscopy with near edge X-ray absorption fine structure spectroscopy (STXM/NEXAFS). Samples were collected at the ground site located in Point Reyes National Seashore, approximately 1 km from the coast. This manuscript focuses on the analysis of individual particles sampled from air masses that originated over the open ocean and then passed through the area of the California current located along the northern California coast. On the basis of composition, morphology, and chemical bonding information, two externally mixed, distinct classes of sulfur containing particles were identified: chemically modified

25Emissions from biomass burning contribute significantly to water-soluble organic carbon (WSOC) 26 and light-absorbing organic carbon (brown carbon). Ambient atmospheric samples were collected at an 27 urban site in Beijing during winter and summer, along with source samples from residential crop straw 28 burning. Carbonaceous aerosol species, including organic carbon (OC), elemental carbon (EC), WSOC and 29 multiple saccharides as well as water-soluble potassium (K + ) in PM 2.5 (fine particulate matter with size less 30 than 2.5µm) were measured. Chemical signatures of atmospheric aerosols in Beijing during winter and 31 summer days with significant biomass burning influence were identified. Meanwhile, light absorption by 32 WSOC was measured and quantitatively compared to EC at ground level. The results from this study 33 indicated that levoglucosan exhibited consistently high concentrations (209±145 ng m -3 ) in winter. Ratios 34 of levoglucosan/mannosan (L/M) and levoglucosan/galacosan (L/G) indicated that residential biofuel use 35is an important source of biomass burning aerosol in winter in Beijing. Light absorption coefficient per 36 unit ambient WSOC mass calculated at 365 nm is approximately 1.54±0.16 m 2 g -1 in winter and 0.73±0.15 37 m 2 g -1 in summer. Biomass burning derived WSOC accounted for 23±7% and 16±7% of total WSOC 38 mass, and contributed to 17±4% and 19±5% of total WSOC light absorption in winter and summer, 39 respectively. It is noteworthy that, up to 30% of total WSOC light absorption was attributed to biomass 40 burning in significant biomass-burning-impacted summer day. Near-surface light absorption (over the 41 range 300-400 nm) by WSOC was about ~40% of that by EC in winter and ~25% in summer. 42 Keywords: Biomass burning, WSOC, saccharides, levoglucosan, light absorption 43 44 4 / 21 2. Methodology 83 2.1 Sampling of ambient and source samples 84 PM 2.5 (fine particulate matter with size less than 2.5 µm) was collected in the campus of Peking 85 University (39°59′21″N, 116°18′25″E) in the northwestern area of Beijing city, with no obvious emission 86 sources around except two major roads (150 m to the east and 200 m to the south). Situated in a mixed 87 district of teaching, residential and commercial areas, the sampling site is representative of the Beijing 88 urban area. 89 A high volume sampler (VFC-PM 2.5 , Thermo Fisher Scientific Co., U.S., 1.13 m 3 min -1 , 8＂×10＂quartz 90 filter) and a four-channel sampler (TH-16A, Tianhong, China, 16.7 L min -1 , 47 mm i.d. Teflon and quartz 91 filters) were co-located at the site, mounted on the rooftop of a building approximately 20 m above ground 92 level. Particles less than 2.5 micron in aerodynamic diameter were collected by both samplers. Quartz 93 filters (Pallflex, Tissuquartz, 2500 QAT-UP) were used for EC and OC analysis and Teflon filters 94 (Whatman Inc. Clifton, NJ, USA) were used for ion analysis. All quartz filters were pre-baked in a furnace 95 at 550℃ for 6 hours. After sampling, all filter samples were kept frozen at ...

Abstract. This study was part of the Megacities Initiative: Local and Global Research Observations (MILAGRO) field campaign conducted in Mexico City metropolitan area during spring 2006. The physical and chemical transformations of particles aged in the outflow from Mexico City were investigated for the transport event of 22 March 2006. A detailed chemical analysis of individual particles was performed using a combination of complementary microscopy and micro-spectroscopy techniques. The applied techniques included scanning transmission X-ray microscopy (STXM) coupled with near edge X-ray absorption fine structure spectroscopy (NEXAFS) and computer controlled scanning electron microscopy with an energy dispersive X-ray analyzer (CCSEM/EDX). As the aerosol plume evolves from the city center, the organic mass per particle increases and the fraction of carbon-carbon double bonds (associated with elemental carbon) decreases. Organic functional groups enhanced with particle age include: carboxylic acids, alkyl groups, and oxygen bonded alkyl groups. At the city center (T0) the most prevalent aerosol type contained inorganic species (composed of sulfur, nitrogen, oxygen, and potassium) coated with organic material. At the T1 and T2 sites, located northeast of T0 (∼29 km and ∼65 km, respectively), the fraction of homogenously mixed organic particles increased in both Correspondence to: M. K. Gilles (mkgilles@lbl.gov) size and number. These observations illustrate the evolution of the physical mixing state and organic bonding in individual particles in a photochemically active environment.

Recent ice core measurements show lead concentrations increasing since 1970, suggesting new nonautomobile-related sources of Pb are becoming important worldwide (1). Developing a full understanding of the major sources of Pb and other metals is critical to controlling these emissions. During the March, 2006 MILAGRO campaign, single particle measurements in Mexico City revealed the frequent appearance of particles internally mixed with Zn, Pb, Cl, and P. Pb concentrations were as high as 1.14 µg/m 3 in PM 10 and 0.76 µg/m 3 in PM 2.5 . Real time measurements were used to select time periods of interest to perform offline analysis to obtain detailed aerosol speciation. Many Zn-rich particles had needle-like structures and were found to be composed of ZnO and/or Zn(NO 3 ) 2 · 6H 2 O. The internally mixed Pb-Zn-Cl particles represented as much as 73% of the fine mode particles (by number) in the morning hours between 2-5 am. The Pb-Zn-Cl particles were primarily in the submicrometer size range and typically mixed with elemental carbon suggesting a combustion source. The unique single particle chemical associations measured in this study closely match signatures indicative of waste incineration. Our findings also show these industrial emissions play an important role in heterogeneous processing of NO y species. Primary emissions of metal and sodium chloride particles emitted by the same source underwent heterogeneous transformations into nitrate particles as soon as photochemical production of nitric acid began each day at ∼7 am. IntroductionParticulate air pollution is correlated with increased morbidity and mortality through cardiovascular and pulmonary effects (2). Although relatively little is known about the specific chemical constituents responsible for the adverse health effects, metal-containing particles are implicated in a number of studies (3-5). The solubility of metal ions present in particles affects their mobility in the human body while their oxidation state greatly affects their toxicity (5). Other factors such as particle size and shape determine how deep into the respiratory tract a particle may travel. Smaller particles with a compact morphology penetrate deeper into the lungs where they are more likely to be retained by the body (6-8). Anthropogenic particles created by high temperature processes (e.g., combustion and ore processing) possess many of the properties responsible for adverse health effects.In urban areas, anthropogenic sources of submicron metal-containing particles are plentiful. For example, the burning of fossil fuel leads to the association of Ni and V within particles (9). Prior to 2000, tetra-ethyl-lead was used as a gasoline additive in many countries and resulted in traffic related emissions of submicron lead particles (10). In industrial areas, smelting produce particulate emissions rich in heavy metals (11). Combustion of municipal waste produces submicron particles composed of Zn, Pb, and Cl as well as numerous other metals (12). Zn and Pb are often found to be internally ...

This study examined the effect of solvent on the analysis of organic aerosol extracts using electrospray ionization mass spectrometry (ESI-MS). Secondary organic aerosol (SOA) produced by ozonation of d-limonene, as well as several organic molecules with functional groups typical for OA constituents, were extracted in methanol, d3-methanol, acetonitrile, and d3-acetonitrile to investigate the extent and relative rates of reactions between analyte and solvent. High resolution ESI-MS showed that reactions of carbonyls with methanol produce significant amounts of hemiacetals and acetals on time scales ranging from several minutes to several days, with the reaction rates increasing in acidified solutions. Carboxylic acid groups were observed to react with methanol resulting in the formation of esters. In contrast acetonitrile extracts showed no evidence of reactions with analyte molecules, suggesting that acetonitrile is the preferred solvent for SOA extraction. The use of solvent-analyte reactivity as a tool for the improved characterization of functional groups in complex organic mixtures was demonstrated. Direct comparison between mass spectra of the same SOA samples extracted in methanol versus acetonitrile was used to estimate the lower limits for the relative fractions of carbonyls (> or = 42%) and carboxylic acids (> or = 55%) in d-limonene SOA.

Organic aerosol (OA) constitutes a substantial fraction of fine particles and affects both human health and climate. It is becoming clear that OA absorbs light substantially (hence termed Brown Carbon, BrC), adding uncertainties to global aerosol radiative forcing estimations. The few current radiative-transfer and chemical-transport models that include BrC primarily consider sources from biogenic and biomass combustion. However, radiocarbon fingerprinting here clearly indicates that light-absorbing organic carbon in winter Beijing, the capital of China, is mainly due to fossil sources, which contribute the largest part to organic carbon (OC, 67 ± 3%) and its sub-constituents (water-soluble OC, WSOC: 54 ± 4%, and water-insoluble OC, WIOC: 73 ± 3%). The dual-isotope (Δ14C/δ13C) signatures, organic molecular tracers and Beijing-tailored emission inventory identify that this fossil source is primarily from coal combustion activities in winter, especially from the residential sector. Source testing on Chinese residential coal combustion provides direct evidence that intensive coal combustion could contribute to increased light-absorptivity of ambient BrC in Beijing winter. Coal combustion is an important source to BrC in regions such as northern China, especially during the winter season. Future modeling of OA radiative forcing should consider the importance of both biomass and fossil sources.