Organosulfates in Atlanta, Georgia: anthropogenic influences on biogenic secondary organic aerosol formation

Organosulfates are secondary organic aerosol (SOA) products that form from reactions of volatile organic compounds (VOC), such as isoprene, in the presence of sulfate that is primarily emitted by fossil fuel combustion. This study examines the anthropogenic influence on biogenic organosulfate formation at an urban site in Atlanta, Georgia (GA) in the southeastern United States (US). Organosulfates were analyzed in fine particulate matter (PM2.5) collected during August 2015 in Atlanta using hydrophilic interaction liquid chromatography (HILIC), tandem mass spectrometry (MS/MS), and high-resolution time-of-flight (ToF) mass spectrometry. By their MS/MS response, 32 major organosulfate species were identified, selected species were quantified, and other species were semi-quantified using surrogate standards. Organosulfates accounted for 16.5&thinsp;% of PM2.5 organic carbon (OC). Isoprene-derived organosulfates were the most abundant, dominated by methyltetrol sulfate which accounted for 12.6&thinsp;% of PM2.5 OC. Together, the isoprene-derived organosulfates accounted for the majority of the isoprene-derived SOA that had been previously observed in Atlanta, but had not been identified at the molecular level. Other major species included seven monoterpene-derived organosulfates, five diesel and/or biodiesel-derived organosulfates, and three new organosulfates that are also expected to derive from isoprene. Organosulfate species and concentrations in Atlanta were compared to those in a rural forested site in Centreville, Alabama (AL) during summer 2013, which were also dominated by isoprene-derived organosulfates. In Atlanta, isoprene-derived organosulfate concentrations were 2–6 times higher and accounted for twice as much OC. The greatest enhancement in concentration was observed for 2-methylglyceric acid sulfate whose formation is enhanced in the presence of nitrogen oxides (NO and NO2; NOx) and is a tracer for isoprene high-NOx SOA. The isoprene-derived organosulfates indicated a stronger influence of NOx in Atlanta compared to Centreville. Overall, these results suggest that SOA in the southeastern US can be reduced by controlling NOx and SO2 emissions from fossil fuel combustion. This study gives insights into the major organosulfate species that should be targets for future measurements in urban environments and standard development.</p

Source apportionment of organic carbon in Centreville, AL using organosulfates in organic tracer-based positive matrix factorization

Organic tracer-based positive matrix factorization (PMF) was used to apportion fine particulate (PM_(2.5)) organic carbon (OC) to its sources in Centreville, AL, USA, a rural forested site influenced by anthropogenic emissions, during the Southern Oxidant and Aerosol Study (SOAS) in the summer of 2013. Model inputs included organosulfates, a group of organic compounds that are tracers of anthropogenically-influenced biogenic secondary organic aerosols (SOA), as well as, OC, elemental carbon, water-soluble organic carbon, and other organic tracers for primary and secondary sources measured during day and night. The organic tracer-based PMF resolved eight factors that were identified as biomass burning (11%, average contribution to PM_(2.5) OC), vehicle emissions (8%), isoprene SOC formed under low-NO_x conditions (13%), isoprene SOC formed under high-NO_x conditions (11%), SOC formed by photochemical reactions (9%), oxidatively aged biogenic SOC (6%), sulfuric acid-influenced SOC (21%, that also includes isoprene and monoterpene SOC), and monoterpene SOC formed under high-NO_x conditions (21%). These results indicate that OC in Centreville during summer is mainly secondary in origin (81%). Fossil fuel combustion is the major source of NO_x, ozone, and sulfuric acid that play a key role in SOA formation in the southeastern US. Fossil fuel was found to influence 61–76% of OC through vehicle emissions and SOA formation. Together with prescribed burns, which were the major type of biomass burning during this study, the OC influenced by anthropogenic activities reached 87%. The organic tracer-based PMF results were further compared with two complementary source apportionment techniques: PMF factors resolved for submicron organic aerosols measured using aerosol mass spectrometry (AMS) by Xu et al. (2015a) in Centreville during SOAS; biomass burning organic aerosols (BBOA, 11% of OC), isoprene-derived organic aerosols (isoprene-OA, 20% of OC), more-oxidized oxygenated organic aerosols (MO-OOA, 34% of OC), and less-oxidized oxygenated organic aerosols (LO-OOA, 35% of OC); and PM_(2.5) OC apportioned by chemical-mass balance model (CMB), considering the same chemical species as this study, save for organosulfates; biomass burning (5%), diesel engines (2%), gasoline smokers (3%), vegetative detritus (1%), isoprene SOC (23%) and monoterpene SOC (34%), and other (likely biogenic secondary) sources (33%). Overall, this study indicates the primary and secondary sources resolved by the organic tracer-based PMF are in good agreement with CMB and AMS-PMF results, while the organic tracer-based PMF provides additional insight to the SOC formation pathways through the inclusion of organosulfates and other organic tracers measured during day and night

Response of the Aerodyne Aerosol Mass Spectrometer to Inorganic Sulfates and Organosulfur Compounds: Applications in Field and Laboratory Measurements

Organosulfur compounds are important components of secondary organic aerosols (SOA). While the Aerodyne high-resolution time-of-flight aerosol mass spectrometer (AMS) has been extensively used in aerosol studies, the response of the AMS to organosulfur compounds is not well-understood. Here, we investigated the fragmentation patterns of organosulfurs and inorganic sulfates in the AMS, developed a method to deconvolve total sulfate into components of inorganic and organic origins, and applied this method in both laboratory and field measurements. Apportionment results from laboratory isoprene photooxidation experiment showed that with inorganic sulfate seed, sulfate functionality of organic origins can contribute ∼7% of SOA mass at peak growth. Results from measurements in the Southeastern U.S. showed that 4% of measured sulfate is from organosulfur compounds. Methanesulfonic acid was estimated for measurements in the coastal and remote marine boundary layer. We explored the application of this method to unit mass-resolution data, where it performed less well due to interferences. Our apportionment results demonstrate that organosulfur compounds could be a non-negligible source of sulfate fragments in AMS laboratory and field data sets. A reevaluation of previous AMS measurements over the full range of atmospheric conditions using this method could provide a global estimate/constraint on the contribution of organosulfur compounds

Source apportionment of organic carbon in Centreville, AL using organosulfates in organic tracer-based positive matrix factorization

Organic tracer-based positive matrix factorization (PMF) was used to apportion fine particulate (PM_(2.5)) organic carbon (OC) to its sources in Centreville, AL, USA, a rural forested site influenced by anthropogenic emissions, during the Southern Oxidant and Aerosol Study (SOAS) in the summer of 2013. Model inputs included organosulfates, a group of organic compounds that are tracers of anthropogenically-influenced biogenic secondary organic aerosols (SOA), as well as, OC, elemental carbon, water-soluble organic carbon, and other organic tracers for primary and secondary sources measured during day and night. The organic tracer-based PMF resolved eight factors that were identified as biomass burning (11%, average contribution to PM_(2.5) OC), vehicle emissions (8%), isoprene SOC formed under low-NO_x conditions (13%), isoprene SOC formed under high-NO_x conditions (11%), SOC formed by photochemical reactions (9%), oxidatively aged biogenic SOC (6%), sulfuric acid-influenced SOC (21%, that also includes isoprene and monoterpene SOC), and monoterpene SOC formed under high-NO_x conditions (21%). These results indicate that OC in Centreville during summer is mainly secondary in origin (81%). Fossil fuel combustion is the major source of NO_x, ozone, and sulfuric acid that play a key role in SOA formation in the southeastern US. Fossil fuel was found to influence 61–76% of OC through vehicle emissions and SOA formation. Together with prescribed burns, which were the major type of biomass burning during this study, the OC influenced by anthropogenic activities reached 87%. The organic tracer-based PMF results were further compared with two complementary source apportionment techniques: PMF factors resolved for submicron organic aerosols measured using aerosol mass spectrometry (AMS) by Xu et al. (2015a) in Centreville during SOAS; biomass burning organic aerosols (BBOA, 11% of OC), isoprene-derived organic aerosols (isoprene-OA, 20% of OC), more-oxidized oxygenated organic aerosols (MO-OOA, 34% of OC), and less-oxidized oxygenated organic aerosols (LO-OOA, 35% of OC); and PM_(2.5) OC apportioned by chemical-mass balance model (CMB), considering the same chemical species as this study, save for organosulfates; biomass burning (5%), diesel engines (2%), gasoline smokers (3%), vegetative detritus (1%), isoprene SOC (23%) and monoterpene SOC (34%), and other (likely biogenic secondary) sources (33%). Overall, this study indicates the primary and secondary sources resolved by the organic tracer-based PMF are in good agreement with CMB and AMS-PMF results, while the organic tracer-based PMF provides additional insight to the SOC formation pathways through the inclusion of organosulfates and other organic tracers measured during day and night

Source apportionment of fine particulate matter in Houston, Texas: insights to secondary organic aerosols

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  ≤  1&thinsp;µm) indicated major contributions from sulfate (averaging 50&thinsp;% by mass), organic aerosol (OA, 40&thinsp;%), and ammonium (14&thinsp;%). Positive matrix factorization (PMF) of AMS data categorized OA on average as 22&thinsp;% hydrocarbon-like organic aerosol (HOA), 29&thinsp;% cooking-influenced less-oxidized oxygenated organic aerosol (CI-LO-OOA), and 48&thinsp;% more-oxidized oxygenated organic aerosol (MO-OOA), with the latter two sources indicative of secondary organic aerosol (SOA). Chemical analysis of PM2.5 (PM  ≤  2.5&thinsp;µm) filter samples agreed that organic matter (35&thinsp;%) and sulfate (21&thinsp;%) 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&thinsp;%), gasoline engines (24.3&thinsp;%), nontailpipe vehicle emissions (11.1&thinsp;%), ship emissions (2.2&thinsp;%), cooking (1.0&thinsp;%), biomass burning (BB, 10.6&thinsp;%), isoprene SOA (11.0&thinsp;%), high-NOx anthropogenic SOA (6.6&thinsp;%), and low-NOx anthropogenic SOA (21.7&thinsp;%). Using available source profiles, CMB apportioned 41&thinsp;% of OC to primary fossil sources (gasoline engines, diesel engines, and ship emissions), 5&thinsp;% to BB, 15&thinsp;% to SOA (including 7.4&thinsp;% biogenic and 7.6&thinsp;% anthropogenic), and 39&thinsp;% to other sources that were not included in the model and are expected to be secondary.This study presents the first application of in situ AMS-PMF, MM-PMF, and CMB for OC source apportionment and the integration of these methods to evaluate the relative roles of biogenic, anthropogenic, and BB-SOA. The three source apportionment models agreed that  ∼ &thinsp;50&thinsp;% of OC is associated with primary emissions from fossil fuel use, particularly motor vehicles. Differences among the models reflect their ability to resolve sources based upon the input chemical measurements, with molecular marker-based methods providing greater source specificity and resolution for minor sources. By combining results from MM-PMF and CMB, BB was estimated to contribute 11&thinsp;% of OC, with 5&thinsp;% primary emissions and 6&thinsp;% BB-SOA. SOA was dominantly anthropogenic (28&thinsp;%) rather than biogenic (11&thinsp;%) or BB-derived. The three-model approach demonstrates significant contributions of anthropogenic SOA to fine PM. More broadly, the findings and methodologies presented herein can be used to advance local and regional understanding of anthropogenic contributions to SOA.</p

Response of the Aerodyne Aerosol Mass Spectrometer to Inorganic Sulfates and Organosulfur Compounds: Applications in Field and Laboratory Measurements

Organosulfur compounds are important components of secondary organic aerosols (SOA). While the Aerodyne high-resolution time-of-flight aerosol mass spectrometer (AMS) has been extensively used in aerosol studies, the response of the AMS to organosulfur compounds is not well-understood. Here, we investigated the fragmentation patterns of organosulfurs and inorganic sulfates in the AMS, developed a method to deconvolve total sulfate into components of inorganic and organic origins, and applied this method in both laboratory and field measurements. Apportionment results from laboratory isoprene photooxidation experiment showed that with inorganic sulfate seed, sulfate functionality of organic origins can contribute ∼7% of SOA mass at peak growth. Results from measurements in the Southeastern U.S. showed that 4% of measured sulfate is from organosulfur compounds. Methanesulfonic acid was estimated for measurements in the coastal and remote marine boundary layer. We explored the application of this method to unit mass-resolution data, where it performed less well due to interferences. Our apportionment results demonstrate that organosulfur compounds could be a non-negligible source of sulfate fragments in AMS laboratory and field data sets. A reevaluation of previous AMS measurements over the full range of atmospheric conditions using this method could provide a global estimate/constraint on the contribution of organosulfur compounds

Qualitative and quantitative analysis of atmospheric organosulfates in Centreville, Alabama

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 (PM_2.5) 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 PM_2.5 concentrations. Together, the quantified organosulfates accounted for  &lt;  0.3 % of organic carbon mass in PM_2.5. To gain insights into other organosulfates in PM_2.5 collected from Centreville, semi-quantitative analysis was employed by way of monitoring characteristic product ions of organosulfates (HSO₄⁻ at <i>m</i>∕<i>z</i> 97 and SO₄^− ⋅ at <i>m</i>∕<i>z</i> 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 <i>m</i>∕<i>z</i> 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

Source apportionment of organic carbon in Centreville, AL using organosulfates in organic tracer-based positive matrix factorization

Organic tracer-based positive matrix factorization (PMF) was used to apportion fine particulate (PM2.5) organic carbon (OC) to its sources in Centreville, AL, USA, a rural forested site influenced by anthropogenic emissions, during the Southern Oxidant and Aerosol Study (SOAS) in the summer of 2013. Model inputs included organosulfates, a group of organic compounds that are tracers of anthropogenically-influenced biogenic secondary organic aerosols (SOA), as well as, OC, elemental carbon, water-soluble organic carbon, and other organic tracers for primary and secondary sources measured during day and night. The organic tracer-based PMF resolved eight factors that were identified as biomass burning (11%, average contribution to PM2.5 OC), vehicle emissions (8%), isoprene SOC formed under low-NOx conditions (13%), isoprene SOC formed under high-NOx conditions (11%), SOC formed by photochemical reactions (9%), oxidatively aged biogenic SOC (6%), sulfuric acid-influenced SOC (21%, that also includes isoprene and monoterpene SOC), and monoterpene SOC formed under high-NOx conditions (21%). These results indicate that OC in Centreville during summer is mainly secondary in origin (81%). Fossil fuel combustion is the major source of NOx, ozone, and sulfuric acid that play a key role in SOA formation in the southeastern US. Fossil fuel was found to influence 61-76% of OC through vehicle emissions and SOA formation. Together with prescribed burns, which were the major type of biomass burning during this study, the OC influenced by anthropogenic activities reached 87%. The organic tracer-based PMF results were further compared with two complementary source apportionment techniques: PMF factors resolved for submicron organic aerosols measured using aerosol mass spectrometry (AMS) by Xu et al. (2015a) in Centreville during SOAS; biomass burning organic aerosols (BBOA, 11% of OC), isoprene-derived organic aerosols (isoprene-OA, 20% of OC), more-oxidized oxygenated organic aerosols (MO-OOA, 34% of OC), and less-oxidized oxygenated organic aerosols (LO-OOA, 35% of OC); and PM2.5 OC apportioned by chemical-mass balance model (CMB), considering the same chemical species as this study, save for organosulfates; biomass burning (5%), diesel engines (2%), gasoline smokers (3%), vegetative detritus (1%), isoprene SOC (23%) and monoterpene SOC (34%), and other (likely biogenic secondary) sources (33%). Overall, this study indicates the primary and secondary sources resolved by the organic tracer-based PMF are in good agreement with CMB and AMS-PMF results, while the organic tracer-based PMF provides additional insight to the SOC formation pathways through the inclusion of organosulfates and other organic tracers measured during day and night. © 2018 Elsevier Lt