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Environmental context: Organosulfates in the atmosphere are an indicator that particulate matter has formed from gases in the presence of anthropogenic pollution. By characterising organosulfates in atmospheric fine particulate matter from the Midwestern USA, we found that organosulfates account for a significant fraction of organic carbon and that they are associated with both plant-derived and anthropogenic gases. Our results demonstrate that anthropogenic pollution significantly influences atmospheric particle concentrations and composition. Organosulfates are components of secondary organic aerosol resulting from the oxidation of volatile organic compounds in the presence of acidic sulfate. This study characterises organosulfates in the Midwestern United States for the first time. In fine particulate matter (PM2.5) collected in Iowa City, IA, in September 2017, organosulfates were analysed using liquid chromatography coupled to high-resolution and tandem mass spectrometry (MS) to identify and quantify (or semi-quantify) major species. Among the 22 identified species, methyltetrol sulfate (m / z 215; C5H11SO7−) had the largest contribution to the bisulfate (m / z 97) product ion, as determined by precursor-ion MS/MS (59.5 % of signal), followed by ten other isoprene-derived organosulfates (15.2 %), seven monoterpene-derived organosulfates (5.6 %), three anthropogenic organosulfates (4.3 %) and one species of unknown origin (0.6 %). Among the quantified species were hydroxyacetone sulfate (4.8 ± 1.1 ng m−3), glycolic acid sulfate (21.0 ± 1.5 ng m−3), 2-methylgyceric acid sulfate (15.1 ± 0.8 ng m−3), C5H7SO7− (m / z 211; 17.9 ± 0.9 ng m−3), C5H9SO7− (m / z 213; 16.0 ± 1.0 ng m−3), and methyltetrol sulfate (214 ± 8 ng m−3); together, these species accounted for 4.4 % of organic carbon. To further validate the measurement of organic species in PM using filter samples, the stability of organosulfates on filters frozen at −20 °C was evaluated over the course of 1 year. The stored samples revealed no degradation of organosulfates, indicating their stability on filters stored frozen for extended periods of time. This study provides new insight into the abundance and identity of organosulfates in the Midwestern US and demonstrates that isoprene-derived organosulfates, in particular, are a significant contributor to PM2.5 organic carbon. Environmental context. Organosulfates in the atmosphere are an indicator that particulate matter has formed from gases in the presence of anthropogenic pollution. By characterising organosulfates in atmospheric fine particulate matter from the Midwestern USA, we found that organosulfates account for a significant fraction of organic carbon and that they are associated with both plant-derived and anthropogenic gases. Our results demonstrate that anthropogenic pollution significantly influences atmospheric particle concentrations and composition. [ABSTRACT FROM AUTHOR]

Online and offline measurements of ambient particulate matter (PM) near the urban and industrial Houston Ship Channel in Houston, Texas, USA, during May 2015 were utilized to characterize its chemical composition and to evaluate the relative contributions of primary, secondary, biogenic, and anthropogenic sources. Aerosol mass spectrometry (AMS) on nonrefractory PM1 (PM ≤ 1µm) indicated major contributions from sulfate (averaging 50% by mass), organic aerosol (OA, 40%), and ammonium (14%). Positive matrix factorization (PMF) of AMS data categorized OA on average as 22% hydrocarbon-like organic aerosol (HOA), 29% cooking-influenced less-oxidized oxygenated organic aerosol (CI-LO-OOA), and 48% more-oxidized oxygenated organic aerosol (MO-OOA), with the latter two sources indicative of secondary organic aerosol (SOA). Chemical analysis of PM2.5 (PM ≤ 2.5µm) filter samples agreed that organic matter (35%) and sulfate (21%) were the most abundant components. Organic speciation of PM2.5 organic carbon (OC) focused on molecular markers of primary sources and SOA tracers derived from biogenic and anthropogenic volatile organic compounds (VOCs). The sources of PM2.5 OC were estimated using molecular marker-based positive matric factorization (MM-PMF) and chemical mass balance (CMB) models. MM-PMF resolved nine factors that were identified as diesel engines (11.5%), gasoline engines (24.3%), nontailpipe vehicle emissions (11.1%), ship emissions (2.2%), cooking (1.0%), biomass burning (BB, 10.6%), isoprene SOA (11.0%), high-NOx anthropogenic SOA (6.6%), and low-NOx anthropogenic SOA (21.7%). Using available source profiles, CMB apportioned 41% of OC to primary fossil sources (gasoline engines, diesel engines, and ship emissions), 5% to BB, 15% to SOA (including 7.4% biogenic and 7.6% anthropogenic), and 39% to other sources that were not included in the model and are expected to be secondary. [ABSTRACT FROM AUTHOR]

Combustion of biomass, garbage, and fossil fuels in South Asia has led to poor air quality in the region and has uncertain climate forcing impacts. Online measurements of submicron aerosol (PM1) emissions were conducted as part of the Nepal Ambient Monitoring and Source Testing Experiment (NAMaSTE) to investigate and report emission factors (EFs) and vacuum aerodynamic diameter (dva) size distributions from prevalent but poorly characterized combustion sources. The online aerosol instrumentation included a "mini" aerosol mass spectrometer (mAMS) and a dual-spot eight-channel aethalometer (AE33). The mAMS measured non-refractory PM1 mass, composition, and size. The AE33-measured black carbon (BC) mass and estimated light absorption at 370 nm due to organic aerosol or brown carbon. Complementary gas-phase measurements of carbon dioxide (CO2), carbon monoxide (CO), and methane (CH4) were collected using a Picarro Inc. cavity ring-down spectrometer (CRDS) to calculate fuel-based EFs using the carbon mass balance approach. The investigated emission sources include open garbage burning, diesel-powered irrigation pumps, idling motorcycles, traditional cookstoves fueled with dung and wood, agricultural residue fires, and coal-fired brick-making kilns, all of which were tested in the field. Open-garbage-burning emissions, which included mixed refuse and segregated plastics, were found to have some of the largest PM1 EFs (3.77-19.8 g kg-1) and the highest variability of the investigated emission sources. Nonrefractory organic aerosol (OA) size distributions measured by the mAMS from garbage-burning emissions were observed to have lognormal mode dva values ranging from 145 to 380 nm. Particle-phase hydrogen chloride (HCl) was observed from open garbage burning and was attributed to the burning of chlorinated plastics. Emissions from two diesel-powered irrigation pumps with different operational ages were tested during NAMaSTE. Organic aerosol and BC were the primary components of the emissions and the OA size distributions were centered at *** 80 nm dva. The older pump was observed to have significantly larger EFOA than the newer pump (5.18 g kg-1 compared to 0.45 g kg-1) and similar EFBC. Emissions from two distinct types of coal-fired brick-making kilns were investigated. The less advanced, intermittently fired clamp kiln was observed to have relatively large EFs of inorganic aerosol, including sulfate (0.48 g kg-1) and ammonium (0.17 g kg-1), compared to the other investigated emission sources. The clamp kiln was also observed to have the largest absorption Ångström exponent (AAED4) and organic carbon (OC) to BC ratio (OC V BCD52). The continuously fired zigzag kiln was observed to have the largest fraction of sulfate emissions with an EFSO4 of 0.96 g kg-1. Non-refractory aerosol size distributions for the brick kilns were centered at **** 400 nm dva. The biomass burning samples were all observed to have significant fractions of OA and non-refractory chloride; based on the size distribution results, the chloride was mostly externally mixed from the OA. The dung-fueled traditional cookstoves were observed to emit ammonium, suggesting that the chloride emissions were partially neutralized. In addition to reporting EFs and size distributions, aerosol optical properties and mass ratios of OC to BC were investigated to make comparisons with other NAMaSTE results (i.e., online photoacoustic extinctiometer (PAX) and off-line filter based) and the existing literature. This work provides critical field measurements of aerosol emissions from important yet undercharacterized combustion sources common to South Asia and the developing world. [ABSTRACT FROM AUTHOR]

Products of secondary organic aerosol (SOA) from aromatic volatile organic compounds (VOCs) - 2,3-dihydroxy-4-oxopentanoic acid, dicarboxylic acids, nitromonoaromatics, and furandiones - were evaluated for their potential to serve as anthropogenic SOA tracers with respect to their (1) ambient concentrations and detectability in PM2.5 in Iowa City, IA, USA; (2) gas-particle partitioning behaviour; and (3) source specificity by way of correlations with primary and secondary source tracers and literature review. A widely used tracer for toluene-derived SOA, 2,3-dihydroxy-4-oxopentanoic acid was only detected in the particle phase (Fp = 1) at low but consistently measurable ambient concentrations (averaging 0.3 ng m-3). Four aromatic dicarboxylic acids were detected at relatively higher concentrations (9.1-34.5 ng m-3), of which phthalic acid was the most abundant. Phthalic acid had a low particle-phase fraction (Fp = 0.26) likely due to quantitation interferences from phthalic anhydride, while 4-methylphthalic acid was predominantly in the particle phase (Fp = 0.82). Phthalic acid and 4-methylphthalic acid were both highly correlated with 2,3-dihydroxy-4-oxopentanoic acid (rs = 0.73, p = 0.003; rs = 0.80, p < 0.001, respectively), suggesting that they were derived from aromatic VOCs. Isophthalic and terephthalic acids, however, were detected only in the particle phase (Fp = 1), and correlations suggested association with primary emission sources. Nitromonoaromatics were dominated by particle-phase concentrations of 4-nitrocatechol (1.6 ng m-3) and 4-methyl-5-nitrocatechol (1.6 ng m-3) that were associated with biomass burning. Meanwhile, 4-hydroxy-3-nitrobenzyl alcohol was detected in a lower concentration (0.06 ng m-3) in the particle phase only (Fp = 1) and is known as a product of toluene photooxidation. Furandiones in the atmosphere have only been attributed to the photooxidation of aromatic hydrocarbons; however the substantial partitioning toward the gas phase (Fp ≤ 0.16) and their water sensitivity limit their application as tracers. The outcome of this study is the demonstration that 2,3-dihydroxy-4-oxopentanoic acid, phthalic acid, 4-methylphthalic acid, and 4-hydroxy-3-nitrobenzyl alcohol are good candidates for tracing SOA from aromatic VOCs. [ABSTRACT FROM AUTHOR]

Organosulfates are components of secondary organic aerosols (SOA) that form from oxidation of volatile organic compounds (VOCs) in the presence of sulfate. In this study, the composition and abundance of organosulfates were determined in fine particulate matter (PM2.5) collected from Centreville, AL, during the Southern Oxidant and Aerosol Study (SOAS) in summer 2013. Six organosulfates were quantified using hydrophilic interaction liquid chromatography (HILIC) with triple quadrupole mass spectrometry (TQD) against authentic standards. Among these, the three most abundant species were glycolic acid sulfate (0.5–52.5 ng m−3), lactic acid sulfate (0.5–36.7 ng m−3), and hydroxyacetone sulfate (0.5–14.3 ng m−3). These three species were strongly inter-correlated, suggesting similar precursors and/or formation pathways. Further correlations with sulfate, isoprene, and isoprene oxidation products indicate important roles for these precursors in organosulfate formation in Centreville. Positive filter sampling artifacts associated with these organosulfates due to gas adsorption or reaction of gas phase precursors of organosulfates with sulfuric acid were assessed for a subset of samples and were less than 7.8 % of their PM2.5 concentrations. Together, the quantified organosulfates accounted for  <  0.3 % of organic carbon mass in PM2.5. To gain insights into other organosulfates in PM2.5 collected from Centreville, semi-quantitative analysis was employed by way of monitoring characteristic product ions of organosulfates (HSO4− at m∕z 97 and SO4− ⋅  at m∕z 96) and evaluating relative signal strength by HILIC–TQD. Molecular formulas of organosulfates were determined by high-resolution time-of-flight (TOF) mass spectrometry. The major organosulfate signal across all samples corresponded to 2-methyltetrol sulfates, which accounted for 42–62 % of the total bisulfate ion signal. Conversely, glycolic acid sulfate, the most abundant organosulfate quantified in this study, was 0.13–0.57 % of the total bisulfate ion signal. Precursors of m/z 96 mainly consisted of nitro-oxy organosulfates. Organosulfates identified were mainly associated with biogenic VOC precursors, particularly isoprene and to a lesser extent monoterpenes and 2-methyl-3-buten-2-ol (MBO). While a small number of molecules dominated the total organosulfate signal, a large number of minor species were also present. This study provides insights into the major organosulfate species in the southeastern US, as measured by tandem mass spectrometry that should be targets for future standard development and quantitative analysis. [ABSTRACT FROM AUTHOR]

Emission rates and properties of ice nucleating particles (INPs) are required for proper representation of aerosol-cloud interactions in atmospheric models. Few investigations have quantified marine INP emissions, a potentially important INP source for remote oceanic regions. Previous studies have suggested INPs in sea spray aerosol (SSA) are linked to oceanic biological activity. This proposed link was explored in this study by measuring INP emissions from nascent SSA during phytoplankton blooms during two mesocosm experiments. In a Marine Aerosol Reference Tank (MART) experiment, a phytoplankton bloom was produced with chlorophyll-a (Chl a) concentrations reaching 39μgL-1, while Chl a concentrations more representative of natural ocean conditions were obtained during the Investigation into Marine Particle Chemistry and Transfer Science (IMPACTS; peak Chl a of 5 μg L-1) campaign, conducted in the University of California, San Diego, wave flume. Dynamic trends in INP emissions occurred for INPs active at temperatures > -30°C. Increases in INPs active between -25° and -15°C lagged the peak in Chl a in both studies, suggesting a consistent population of INPs associated with the collapse of phytoplankton blooms. Trends in INP emissions were also compared to aerosol composition, abundances of microbes, and enzyme activity. In general, increases in INP concentrations corresponded to increases in organic species in SSA and the emissions of heterotrophic bacteria, suggesting that both microbes and biomolecules contribute to marine INP populations. INP trends were not directly correlated with a single biological marker in either study. Direct measurements of INP chemistry are needed to accurately identify particles types contributing to marine INP populations. [ABSTRACT FROM AUTHOR]

Bioaerosols pose risks to human health and agriculture and may influence the evolution of mixed-phase clouds and the hydrological cycle on local and regional scales. The availability and reliability of methods and data on the abundance and properties of atmospheric bioaerosols, however, are rather limited. Here we analyze and compare data from different real-time ultraviolet laser/lightinduced fluorescence (UV-LIF) instruments with results from a culture-based spore sampler and offline molecular tracers for airborne fungal spores in a semi-arid forest in the southern Rocky Mountains of Colorado. Commercial UVAPS (ultraviolet aerodynamic particle sizer) and WIBS-3 (wideband integrated bioaerosol sensor, version 3) instruments with different excitation and emission wavelengths were utilized to measure fluorescent aerosol particles (FAPs) during both dry weather conditions and periods heavily influenced by rain. Seven molecular tracers of bioaerosols were quantified by analysis of total suspended particle (TSP) high-volume filter samples using a high-performance anionexchange chromatography system with pulsed amperometric detection (HPAEC-PAD). From the same measurement campaign, Huffman et al. (2013) previously reported dramatic increases in total and fluorescent particle concentrations during and immediately after rainfall and also showed a strong relationship between the concentrations of FAPs and ice nuclei (Huffman et al., 2013; Prenni et al., 2013). Here we investigate molecular tracers and show that during rainy periods the atmospheric concentrations of arabitol (35.2 ± 10.5 ng m-3) and mannitol (44.9 ± 13.8 ng m-3) were 3-4 times higher than during dry periods. During and after rain, the correlations between FAP and tracer mass concentrations were also significantly improved. Fungal spore number concentrations on the order of 104 m-3, accounting for 2-5% of TSP mass during dry periods and 17-23% during rainy periods, were obtained from scaling the tracer measurements and from multiple analysis methods applied to the UV-LIF data. Endotoxin concentrations were also enhanced during rainy periods, but showed no correlation with FAP concentrations. Average mass concentrations of erythritol, levoglucosan, glucose, and (1→3)-β-D-glucan in TSP samples are reported separately for dry and rainy weather conditions. Overall, the results indicate that UV-LIF measurements can be used to infer fungal spore concentrations, but substantial development of instrumental and data analysis methods appears to be required for improved quantification. [ABSTRACT FROM AUTHOR]

Single-scattering albedo (SSA) and absorption Ångström exponent (AAE) are two critical parameters in determining the impact of absorbing aerosol on the Earth's radiative balance. Aerosol emitted by biomass burning represent a significant fraction of absorbing aerosol globally, but it remains difficult to accurately predict SSA and AAE for biomass burning aerosol. Black carbon (BC), brown carbon (BrC), and non-absorbing coatings all make substantial contributions to the absorption coefficient of biomass burning aerosol. SSA and AAE cannot be directly predicted based on fuel type because they depend strongly on burn conditions. It has been suggested that SSA can be effectively parameterized via the modified combustion efficiency (MCE) of a biomass burning event and that this would be useful because emission factors for CO and CO2, from which MCE can be calculated, are available for a large number of fuels. Here we demonstrate, with data from the FLAME-4 experiment, that for a wide variety of globally relevant biomass fuels, over a range of combustion conditions, parameterizations of SSA and AAE based on the elemental carbon (EC) to organic carbon (OC) mass ratio are quantitatively superior to parameterizations based on MCE.We show that the EC/OC ratio and the ratio of EC / (EC+OC) both have significantly better correlations with SSA than MCE. Furthermore, the relationship of EC / (EC+OC) with SSA is linear. These improved parameterizations are significant because, similar to MCE, emission factors for EC (or black carbon) and OC are available for a wide range of biomass fuels. Fitting SSA with MCE yields correlation coefficients (Pearson's r) of ~0.65 at the visible wavelengths of 405, 532, and 660 nm while fitting SSA with EC / OC or EC / (EC+OC) yields a Pearson's r of 0.94-0.97 at these same wavelengths. The strong correlation coefficient at 405 nm (r =0.97) suggests that parameterizations based on EC / OC or EC / (EC+OC) have good predictive capabilities even for fuels in which brown carbon absorption is significant. Notably, these parameterizations are effective for emissions from Indonesian peat, which have very little black carbon but significant brown carbon (SSA=0.990±0.001 at 532 and 660 nm, SSA=0.937±0.011 at 405 nm). Finally, we demonstrate that our parameterization based on EC / (EC+OC) accurately predicts SSA during the first few hours of plume aging with data from Yokelson et al. (2009) gathered during a biomass burning event in the Yucatán Peninsula of Mexico. [ABSTRACT FROM AUTHOR]

Abstract: Organosulfates have recently been observed in ambient atmospheres as a component of aerosol organic matter. This study presents the first characterization of organosulfates in Asia and demonstrates their ubiquity and chemical diversity, yet minor contribution to fine particulate mass. Organosulfates were characterized in ambient aerosol by ultra-performance liquid chromatography and high-resolution mass spectrometry, which allowed for experimental determination of molecular formulas and estimation of atmospheric abundance. Aerosols were analyzed from four sites spanning urban and remote locations, including Hanimaadhoo, Maldives, Gosan, Korea, Singapore, and Lahore, Pakistan. Semi-quantitative analysis yielded average estimates of OS accounting for less than 1% of PM2.5 mass, 2.3% of organic carbon, and 3.8% of total sulfate. The majority of the observed compounds were attributed to biogenic secondary organic aerosol from isoprene or monoterpenes. New organosulfates are also reported. [Copyright &y& Elsevier]

Abstract: The high-molecular weight water-soluble organic compounds present in atmospheric aerosols underwent functional-group characterization using liquid chromatography tandem mass spectrometry (LC-MS/MS), with a focus on understanding the chemical structure and origins of humic-like substances (HULIS) in the atmosphere. Aerosol samples were obtained from several locations in North America at times when primary sources contributing to organic aerosol were well-characterized: Riverside, CA, Fresno, CA, urban and peripheral Mexico City, Atlanta, GA, and Bondville, IL. Chemical analysis targeted identification and quantification of functional groups, such as aliphatic, aromatic, and bulk carboxylic acids, organosulfates, and carbohydrate-like substances that comprise species with molecular weights (MW) 200–600 amu. Measured high-MW functional groups were compared to modeled primary sources with the purpose of identifying associations between aerosol sources, high-MW aerosol species, and HULIS. Mobile source emissions were linked to high-molecular weight carboxylic acids, especially aromatic acids, biomass burning was associated with carboxylic acids and carbohydrate-like substances, and secondary organic aerosol (SOA) correlated well with the total amount of HULIS measured, whereas organosulfates showed no correlation with aerosol sources and exhibited unique spatial trends. These results suggested the importance of motor vehicles, biomass burning, and SOA as important sources of precursors to HULIS. Structural characteristics of atmospheric HULIS were compared to terrestrial humic and fulvic acids and revealed striking similarities in chemical structure, with the exception of organosulfates which were unique to atmospheric HULIS. [Copyright &y& Elsevier]

Primary and secondary sources contributing to atmospheric organic aerosol during the months of July and August were quantitatively assessed in three North American urban areas: Cleveland, Ohio, and Detroit, Michigan, in the Midwest region and Riverside, California, in the Los Angeles Air Basin. Organic molecular marker species unique to primary aerosol sources and secondary tracers derived from isoprene, α-pinene, β-caryophyllene, and toluene were measured using gas chromatography-mass spectrometry. Source contributions from motor vehicles, biomass burning, vegetative detritus, and secondary organic aerosol (SOA) were estimated using chemical mass balance (CMB) modeling. In Cleveland, primary sources accounted for 37 ± 2% of ambient organic carbon, measured biogenic and anthropogenic secondary sources contributed 46 ± 6%, and other unknown sources contributed 17 ± 4%. Similarly, Detroit aerosol was determined to be 44 ± 5% primary and 37 ± 3% secondary, while 19 ± 7% was unaccounted for by measured sources. In Riverside, 21 ± 3% of organic carbon came from primary sources, 26 ± 5% was attributed to measured secondary sources, and 53 ± 3% came from other sources that were expected to be secondary in nature. The comparison of samples across these two regions demonstrated that summertime SOA in the Midwestern United States was substantially different from the summertime SOA in the Los Angeles Air Basin and indicated the need to exert caution when generalizing about the sources and nature of SOA across different urban areas. Furthermore, the results of this study suggest that the contemporary understanding of SOA sources and formation mechanisms is satisfactory to explain the majority of SOA in the Midwest Additional SOA sources and mechanisms of formation are needed to explain the majority of SOA in the Los Angeles Air Basin. [ABSTRACT FROM AUTHOR]

Furandiones are products of the photooxidation of anthropogenic volatile organic compounds (VOC), like toluene, and contribute to secondary organic aerosol (SOA). Because few molecular tracers of anthropogenic SOA are used to assess this source in ambient aerosol, developing a quantification method for furandiones holds a great importance. In this study, we developed a direct and highly sensitive gas chromatography-mass spectrometry method for the quantitative analysis of furandiones in fine particulate matter that is mainly free from interference by structurally-related dicarboxylic acids. Our application of this method in Iowa City, IA provides the first ambient measurements of four furandiones: 2,5-furandione, 3-methyl-2,5-furandione, dihydro-2,5-furandione, and dihydro-3-methyl-2,5-furandione. Furandiones were detected in all collected samples with a daily average concentration of 9.1 ± 3.8 ng m −3 . The developed method allows for the accurate measurement of the furandiones concentrations in ambient aerosol, which will support future evaluation of these compounds as tracers for anthropogenic SOA and assessment of their potential health impacts. [ABSTRACT FROM AUTHOR]

Abstract: The contributions of anthropogenic and biogenic secondary organic carbon (SOC) to total PM2.5 mass are of interest to air quality management agencies required to demonstrate maintenance of the PM2.5 NAAQS. Reductions of SOC can be used in conjunction with the mitigation of other PM2.5 constituents to maintain PM2.5 concentrations below the regulatory limit. Currently, quantitative tools to understand the SOC source contributions to PM2.5 mass are not well developed, and the spatial variation of different types of SOC is not known. In this study concentrations of anthropogenic and biogenic SOC mass were determined using PM2.5 measurements made in Cleveland, OH and Mingo Junction, OH. Twenty-four hour averaged samples were collected on the EPA 1-in-6 day schedule over the course of one year between June 2007 and May of 2008. Organic molecular markers for anthropogenic and biogenic SOC were extracted from the PM2.5, silylated, and then analyzed by GC–MS. Source apportionment calculations were conducted using the EPA CMB (v.8.2) software and organic molecular markers as source tracers. SOC concentrations calculated from SOC tracers measurements followed the expected seasonal patterns with maximum contributions during the summer and minimum contributions during the winter. Anthropogenic SOC constituted approximately 37% to the apportioned SOC and 6% to the measured OC, on average across both sites. Biogenic SOC contributed the 42% to the apportioned SOC, and 4% to the measured OC. Anthropogenic SOC contributed strongly to organic PM2.5 meaning that SOC may by partially controllable by reductions in VOC emissions from anthropogenic sources. Similarities in the month-to-month patterns in α-pinene markers were observed between Cleveland and Mingo Junction, suggesting a regional character to this type of SOC. However, such patterns were not readily apparent in the isoprene markers. Limitations were found in the current version of the model. Approximately half of the water soluble organic carbon unrelated to biomass burning (NB-WSOC) during spring, summer and early fall could not be apportioned by the CMB model with the SOC markers available during this study. This suggested that additional sources not included in the CMB model used in this study contributed to SOC, or that models using markers measured in chamber oxidations are not entirely representative of the study sites. The unapportioned OC did not correlate particularly well with any of the known OC sources. While performance of the model is limited due to uncertainties in the source profiles, the apportionments calculated still give a preliminary insight into the relative contributions to SOC from anthropogenic and biogenic emissions. [Copyright &y& Elsevier]

Sea spray aerosol (SSA) is a globally important source of particulate matter. A mesocosm study was performed to determine the relative enrichment of saccharides and inorganic ions in nascent fine (PM2.5) and coarse (PM10-2.5) SSA and the sea surface microlayer (SSML) relative to bulk seawater. Saccharides comprise a significant fraction of organic matter in fine and coarse SSA (11 and 27%, respectively). Relative to sodium, individual saccharides were enriched 14-1314-fold in fine SSA, 3-138-fold in coarse SSA, but only up to 1.0-16.2-fold in SSML. Enrichments in SSML were attributed to rising bubbles that scavenge surface-active species from seawater, while further enrichment in fine SSA likely derives from bubble films. Mean enrichment factors for major ions demonstrated significant enrichment in fine SSA for potassium (1.3), magnesium (1.4), and calcium (1.7), likely because of their interactions with organic matter. Consequently, fine SSA develops a salt profile significantly different from that of seawater. Maximal enrichments of saccharides and ions coincided with the second of two phytoplankton blooms, signifying the influence of ocean biology on selective mass transfer across the ocean-air interface. [ABSTRACT FROM AUTHOR]

Organosulfates (OS) are important components of secondary organic aerosol (SOA) that have been identified in numerous field studies. This class of compounds within SOA can potentially affect aerosol physicochemical properties such as hygroscopicity because of their polar and hydrophilic nature as well as their low volatility. Currently, there is a dearth of information on how aerosol particles that contain OS interact with water vapor in the atmosphere. Herein we report a laboratory investigation on the hygroscopic properties of a structurally diverse set of OS salts at varying relative humidity (RH) using a Hygroscopicity-Tandem Differential Mobility Analyzer (H-TDMA). The OS studied include the potassium salts of glycolic acid sulfate, hydroxyacetone sulfate, 4-hydroxy-2,3-epoxybutane sulfate, and 2-butenediol sulfate and the sodium salts of benzyl sulfate, methyl sulfate, ethyl sulfate, and propyl sulfate. In addition, mixtures of OS and sodium chloride were also studied. The results showed gradual deliquescence of these aerosol particles characterized by continuous uptake and evaporation of water in both hydration and dehydration processes for the OS, while the mixture showed prompt deliquescence and effloresce transitions, albeit at a lower relative humidity relative to pure sodium chloride. Hygroscopic growth of these OS at 85% RH were also fit to parameterized functional forms. This new information provided here has important implications about the atmospheric lifetime, light scattering properties, and the role of OS in cloud formation. Moreover, results of these studies can ultimately serve as a basis for the development and evaluation of thermodynamic models for these compounds in order to consider their impact on the atmosphere. [ABSTRACT FROM AUTHOR]

Atmospheric aerosols are often collected on substrates and analyzed weeks or months after the initial collection. We investigated how the selection of substrate and microscopy method influence the measured size, phase, and morphology of sea spray aerosol (SSA) particles and how sample storage conditions affect individual particles using three common microscopy techniques: optical microscopy, atomic force microscopy, and scanning electron microscopy. Micro-Raman spectroscopy was used to determine changes in the water content of stored particles. The results show that microscopy techniques operating under ambient conditions provide the most relevant and robust measurement of particle size. Samples stored in a desiccator and at ambient conditions leads to similar sizes and morphologies, while storage that involves freezing and thawing leads to irreversible changes due to phase changes and water condensation. Typically, SSA particles are deposited wet and, if possible, samples used for single-particle analysis should be stored at or near conditions at which they were collected in order to avoid dehydration. However, if samples need to be dry, as is often the case, then this study found that storing SSA particles at ambient laboratory conditions (17-23% RH and 19-21 °C) was effective at preserving them and reducing changes that would alter samples and subsequent data interpretation. [ABSTRACT FROM AUTHOR]

Understanding the interactions ofwater with atmospheric aerosolsis crucial for determining the size, physical state, reactivity, andclimate impacts of this important component of the Earth’satmosphere. Here we show that water uptake and hygroscopic growthof multicomponent, atmospherically relevant particles can be sizedependent when comparing 100 nm versus ca. 6 μm sized particles.It was determined that particles composed of ammonium sulfate withsuccinic acid and of a mixture of chlorides typical of the marineenvironment show size-dependent hygroscopic behavior. Microscopicanalysis of the distribution of components within the aerosol particlesshow that the size dependence is due to differences in the mixingstate, that is, whether particles are homogeneously mixed or phaseseparated, for different sized particles. This morphology-dependenthygroscopicity has consequences for heterogeneous atmospheric chemistryas well as aerosol interactions with electromagnetic radiation andclouds. [ABSTRACT FROM AUTHOR]

The Lake Michigan Ozone Study from 21 May to 23 June 2017 (LMOS 2017) aimed to better understand the anthropogenic and biogenic sources that contribute to ozone and fine particles (PM 2.5) along the coast of Lake Michigan. Here, we focus on the chemical composition of daytime and nighttime PM 2.5 —especially organic carbon, inorganic ions and organosulfates—at a ground-based supersite in Zion, Illinois. PM 2.5 mass concentrations ranged from 1.5 to 12.9 μg m−3 with an average (±standard error) of 5.2 ± 0.4 μg m−3. The most significant contributor to PM 2.5 mass was organic matter (OM; calculated as 1.7 × organic carbon [OC]; contributing an average of 59 ± 2%), followed by sulfate (17 ± 1%), ammonium (6.3 ± 0.3%), nitrate (3.5 ± 0.4%), and elemental carbon (EC; 3.4 ± 0.2%). During each of the three periods of high ozone, PM 2.5 had different regional characteristics. Period A (2–3 June) was impacted by lake breeze and south-easterly air masses that travelled over major urban areas. Period A had the highest daily PM 2.5 mass concentrations (11.4 ± 1.5 μg m−3) and EC with a relatively low OC:EC ratio of 7.0, indicating the influence of sources with low OC:EC ratios, which includes the anthropogenic combustion of fossil fuels and biomass. Period B (10–13 June) was impacted by air masses traveling from the southern US. It had a relatively high OC:EC ratio of 18, the highest PM 2.5 sulfate concentrations and aerosol acidity, and elevated mixing ratios of isoprene along with its oxidation products methyl vinyl ketone (MVK) and methacrolein (MACR). Peak concentrations of organosulfates, including methyltetrol sulfate (m/z 215; C 5 H 11 SO 7 −), were also observed throughout period B. Period C (13–17 June) followed a change to northerly winds. PM 2.5 concentrations decreased along with decreases in sulfate, acidity, and most organosulfates. Throughout the study, organosulfates accounted for an average of 4% of OM and up to 15% of OM in Period B. Organosulfates were largely isoprene-derived, with lessor contributions from monoterpenes (0.3%) and anthropogenic sources (0.5%). Through these measurements of organosulfates in the Great Lakes region, we demonstrate the importance of anthropogenic sulfate emissions and aerosol acidity on SOA formation, and establish that isoprene-derived organosulfates, in particular, contribute significantly to PM 2.5. With other LMOS observations, the chemical signatures of PM 2.5 , and back trajectories show that ozone episodes cooccur with localized lake-breeze meteorology within air masses that vary from episode to episode in chemical history and source region. Image 1 • PM 2.5 composition differed across three periods of elevated ozone. • Isoprene-derived organosulfates contribute substantially to secondary organic aerosol (SOA). • SOA tracers indicate transformations occurred via photooxidation and ozonolysis. • SOA formation was highly sensitive to aerosol acidity and inorganic sulfate. [ABSTRACT FROM AUTHOR]

Tracers of secondary organic aerosols (SOA) from thirteen aromatic hydrocarbons were quantified in laboratory smog chamber experiments. Class-specific SOA tracers emerged, including 2,3-dihydroxy-4-oxo-pentatonic acid (DHOPA) from monoaromatic volatile organic compounds (VOCs), phthalic acid from naphthalene and 1-methylnaphthalene, and methyl-nitrocatechol isomers from o,m,p-cresol oxidation. Organic carbon mass fractions (f SOC) for these and other tracers were determined and extend the SOA tracer method widely used to apportion biogenic secondary organic carbon (SOC). The extended SOA tracer model was applied to evaluate the sources of SOC in Atlanta, GA during summer 2015 and winter 2016 after modifying the chamber-derived f SOC values to reflect SOA yields and local VOC levels (f SOC '). Monoaromatic, diaromatic, and cresol SOC contributed an average of 24%, 8%, and 0.12% of organic carbon (OC) mass during summer and 17%, 5%, and 0.27% during winter, respectively. Cresol SOC peaked during winter and was highly correlated with levoglucosan (r = 0.83, p < 0.001), consistent with its' precursors originating from biomass burning. Together, aromatic, biogenic, and biomass burning derived SOC accounted for an average of 77% and 28% of OC in summer and winter, respectively. The new understanding of SOA composition from aromatic VOCs advances the tracer-based method by including important precursors of SOC and enables a better understanding of the sources of atmospheric aerosol. Image 1 • Secondary organic aerosol (SOA) tracers from 13 aromatic VOC were quantified. • The SOA tracer model was extended and applied in Atlanta, Georgia. • Mono- and di-aromatic VOC contributed 32% of organic carbon in summer 22% in winter. • Biomass burning impacts on SOA were indicated by nitroaromatics from cresols. [ABSTRACT FROM AUTHOR]