High molecular weight SOA formation during limonene ozonolysis: insights from ultrahigh-resolution FT-ICR mass spectrometry characterization

The detailed molecular composition of laboratory generated limonene ozonolysis secondary organic aerosol (SOA) was studied using ultrahigh-resolution Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Approximately 1200 molecular formulas were identified in the SOA over the mass range of 140 to 850 Da. Four characteristic groups of high relative abundance species were observed; they indicate an array of accretion products that retain a large fraction of the limonene skeleton. The identified molecular formulas of each of the groups are related to one another by CH2, O and CH2O homologous series. The CH2 and O homologous series of the low molecular weight (MW) SOA (m/z \u3c 300) are explained with a combination of functionalization and fragmentation of radical intermediates and reactive uptake of gas-phase carbonyls. They include isomerization and elimination reactions of Criegee radicals, reactions between alkyl peroxy radicals, and scission of alkoxy radicals resulting from the Criegee radicals. The presence of compounds with 10–15 carbon atoms in the first group (e.g. C11H18O6) provides evidence for SOA formation by the reactive uptake of gas-phase carbonyls during limonene ozonolysis. The high MW compounds (m/z \u3e 300) were found to constitute a significant number fraction of the identified SOA components. The formation of high MW compounds was evaluated by molecular formula trends, fragmentation analysis of select high MW compounds and a comprehensive reaction matrix including the identified low MW SOA, hydroperoxides and Criegee radicals as building blocks. Although the formation of high MW SOA may occur via a variety of radical and non-radical reaction channels, the combined approach indicates a greater importance of the non-condensation reactions over aldol and ester condensation reaction channels. Among these hemi-acetal reactions appear to be most dominant followed by hydroperoxide and Criegee reaction channels

Aromatic organosulfates in atmospheric aerosols: Synthesis, characterization, and abundance

Aromatic organosulfates are identified and quantified in fine particulate matter (PM2.5) from Lahore, Pakistan, Godavari, Nepal, and Pasadena, California. To support detection and quantification, authentic standards of phenyl sulfate, benzyl sulfate, 3-and 4-methylphenyl sulfate and 2-, 3-, and 4-methylbenzyl sulfate were synthesized. Authentic standards and aerosol samples were analyzed by ultra-performance liquid chromatography (UPLC) coupled to negative electrospray ionization (ESI) quadrupole time-of-flight (ToF) mass spectrometry. Benzyl sulfate was present in all three locations at concentrations ranging from 4 – 90 pg m−3. Phenyl sulfate, methylphenyl sulfates and methylbenzyl sulfates were observed intermittently with abundances of 4 pg m−3, 2-31 pg m−3, 109 pg m−3, respectively. Characteristic fragment ions of aromatic organosulfates include the sulfite radical (•SO3−, m/z 80) and the sulfate radical (•SO4−,m/z 96). Instrumental response factors of phenyl and benzyl sulfates varied by a factor of 4.3, indicating that structurally-similar organosulfates may have significantly different instrumental responses and highlighting the need to develop authentic standards for absolute quantitation organosulfates. In an effort to better understand the sources of aromatic organosulfates to the atmosphere, chamber experiments with the precursor toluene were conducted under conditions that form biogenic organosulfates. Aromatic organosulfates were not detected in the chamber samples, suggesting that they form through different pathways, have different precursors (e.g. naphthalene or methylnaphthalene), or are emitted from primary sources

Seasonal variations of stable carbon isotopic composition of bulk aerosol carbon from Gosan site, Jeju Island in the East China Sea

This study explores the usefulness of stable isotopic composition (delta C-13) along with other chemical tracers and air mass trajectory to identify the primary and secondary sources of carbonaceous aerosols. Aerosol samples (n = 84) were collected continuously from April 2003 to April 2004 at Gosan site in Jeju Island, South Korea. The concentrations of total carbon (TC), HCl fumed carbonate-free total carbon (fumed-TC) and their delta C-13 were measured online using elemental analyzer interfaced to isotope ratio mass spectrometer (EA-IRMS). Similar concentrations of TC and fumed-TC and their similar delta C-13 values suggest the insignificant contribution of inorganic carbon to Gosan aerosols. The monthly averaged delta C-13(TC) showed the lowest in April/May (-24.2 to 24.4 parts per thousand), which is related with the highest concentrations of oxalic acid (a secondary tracer). The result indicates an enhanced contribution of TC from secondary sources. The monthly averaged delta C-13(TC) in July/August (-23.0 to 22.5 parts per thousand) were similar to those in January/February (-23.1 parts per thousand to 22.7 parts per thousand). However, chemical tracers and air mass transport pattern suggest that the pollution source regions in January/February are completely different from those in July/August Higher delta C-13 values in July/August are aligned with higher concentration ratios of marine tracers (azelaic acid/TC and methanesulfonate/TC), suggesting an enhanced contribution of marine organic matter to the aerosol loading. Higher delta C-13 values in January/February are associated with higher concentrations of phthalic acid and K+/TC, indicating more contributions of carbonaceous aerosols from fossil fuel and C-4-plant biomass combustion. This study demonstrates that delta C-13(TG) along with other chemical tracers and air mass trajectory, can be used as a tracer to understand the importance of primary versus secondary pollution sources of carbonaceous aerosols in the atmosphere. (C) 2014 Elsevier Ltd. All rights reserved

Seasonal variation of the concentrations of nitrogenous species and their nitrogen isotopic ratios in aerosols at Gosan, Jeju Island : Implications for atmospheric processing and source changes of aerosols

Atmospheric aerosol samples (n = 84) were collected at Gosan site, Jeju Island, South Korea between April 2003 and April 2004 for the measurements of total nitrogen (TN) and its isotopic ratio (δ15N) as well as nitrogen species (NH4+ and NO3-). Measurements were also conducted for remained nitrogen (remained N) and removed nitrogen (removed N) on HC1 fume treatment. A pronounced seasonal variation was found in the δ15N of TN, remained N (mostly NH4+), and removed N (mostly NO3-). The highest mean δ15N values of TN (+16.9‰ ± 4.5‰) and remained N (+20.2‰ ± 5.2‰) are detected in summer (June-August) whereas the lowest mean δ15N values (+12.9‰ ± 3.4‰ and +11.3‰± 5.1‰, respectively) are in winter (December-February). These trends can partly be explained by an enhanced contribution of 15N-enriched emissions from agricultural straw burning in China in a harvest season (summer and autumn). The mean δ15N of removed N showed an opposite trend: the lowest (+8.9‰ ± 3.7‰) in warm season (March-August) and the highest (+14.1‰ ± 3.7‰) in cold season (September-February). These results can be explained by changes in source regions and emission strengths of nitrogenous species, as well as difference in secondary aerosol nitrogen formation between warm and cold seasons. Higher ratios of Ca2+/Na+ and the lowest ratios of Na+/(Cl- + NO3-) are associated with lower δ15N values of removed N as a result of less isotopic enrichment (εproduct‐reactant) during the reaction between HNO3 and dust particles. This study proposes that 15N/14N ratio can be regarded as process tracer of nitrogenous species in the atmosphere

Seasonal variations of diacids, ketoacids, and α-dicarbonyls in aerosols at Gosan, Jeju Island, South Korea : Implications for sources, formation, and degradation during long-range transport

Aerosol samples (n = 84) were collected continuously from April 2003 to April 2004 at Gosan site in Jeju Island, South Korea. The samples were analyzed for diacids, ketoacids, and α-dicarbonyls, as well as organic carbon (OC), elemental carbon (EC), water‐soluble organic carbon (WSOC), and water-soluble inorganic ions. Oxalic acid (C2) was the most abundant followed by malonic acid (C3) in all the seasons. The mean concentration (784 ng m^[-3]) of total diacids (C2-C12) and their relative abundances in total organic species detected, OC and WSOC were found to be the highest in summer, whereas those of ketoacids and dicarbonyls were the highest in winter. The annual mean contributions of diacids, ketoacids, and dicarbonyls to WSOC are 12, 1, and 0.4%, respectively. They are several times higher than those reported in East Asia from which air masses are transported to Gosan, indicating an importance of photochemical processing of aerosols during a long-range transport. Diacids and related compounds show different seasonal variations, suggesting their season-specific sources and photochemical processing. This study demonstrates an enhanced photochemical production and degradation of water-soluble organics in summer. In contrast, higher positive correlations between combustion tracers (non-sea-salt K+ and EC) and diacids and related compounds were observed in the winter, pointing out higher emission of diacids and related compounds or their precursors from fossil fuel/biomass burning

Diurnal variation in the water-soluble inorganic ions, organic carbon and isotopic compositions of total carbon and nitrogen in biomass burning aerosols from the LBA-SMOCC campaign in Rondônia, Brazil

Aerosol particles (PM2.5) were collected during the day (n=6) and nighttime (n=9) from a tropical pasture site in Rondônia, Brazil during an intensive biomass burning period (16-26 September, 2002). Higher normalized (by K+, levoglucosan, or apparent elemental carbon, ECa) mass concentrations of SO4^[2-] and CH3SO3- in daytime suggest their photochemical production, while the opposite trend for NO3- suggests its transfer to the aerosol phase at lower temperatures and higher humidities, as well as possibly production through hydrolysis of N2O5 on aqueous aerosol particles. About 4.2-7.5% of OC (5-13% of water-soluble organic carbon (WSOC)) could be characterized at the molecular level using GC-MS and GC-FID. Among the detected organic compound classes, the relative abundances of anhydrosugars and aromatics were higher in night samples, but sugars/sugar alcohols, diacids, oxoacids and α-dicarbonyls were more abundant in day samples. Consecutive day and night samples showed that δ13C values of total carbon (TC) were lower in daytime samples, which can be interpreted as resulting from higher contributions of refractory TC depleted in 13C due to predominantly flaming combustion. The δ15N values of total nitrogen (TN) ranged from +23.5‰ to +25.7‰, however, there was no trend in day and night samples. Higher values of δ13C and δ15N for biomass burning particles than those of unburned vegetation reflect positive isotopic enrichment either during the formation of particles or after the emission of particles in the atmosphere

Comparison of Amazonian biomass burning and East Asian marine aerosols : Bulk organics, diacids and related compounds, water-soluble inorganic ions, stable carbon and nitrogen isotope ratios

In this study, biomass burning and marine aerosols collected in the Amazon, Brazil and on an island south of South Korea are compared in terms of chemical characteristics and ageing by the determination of water-soluble organic carbon (WSOC), water-insoluble organic carbon (WIOC), elemental carbon (EC), diacids (C2-C11) and related compounds (ketoacids and α-dicarbonyls), stable carbon isotopic ratios (δ13C) of total carbon (TC), and nitrogen isotopic ratios (δ15N) of total nitrogen (TN). The concentration ratios of WSOC, WIOC, and EC to aerosol mass are 2-12 times higher in biomass burning aerosols than in marine aerosols. In contrast, concentration ratios of water-soluble cations and anions to aerosol mass are lower by a factor of 0.2-0.6 in biomass burning aerosols than in marine aerosols. Among diacids and related compounds, oxalic acid (C2) was found to be the most abundant, followed by succinic acid (C4) in biomass burning aerosols, while malonic acid (C3) dominated in marine aerosols. Lower relative abundances of C2-C4 diacids, unsaturated diacids, and α-dicarbonyls in total diacids and related compounds were observed in biomass burning aerosols than in marine aerosols, whereas those of C5-C11 diacids, branched diacids, multifunctional diacids, and ketoacids were higher in biomass burning aerosols. These results suggest that there are significant differences in the sources and photochemical production pathways of individual diacids and related compounds. While the δ13C values (－26.5 to －20.5‰) of TC and δ15N values (＋6.8 to ＋26.9 ‰) of TN showed a large variation in marine aerosols, the variations were rather small (δ13C:－26.1 to －23.6‰; δ15N: ＋21.5 to ＋25.7‰) in biomass-burning aerosols. We propose that these δ13C and δ15N values can be used to characterize biomass-burning aerosols