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While aqueous-phase processing contributes to the formation of nitrogen-containing organic compounds (NOCs), the detailed pathways are not well understood. In this study, the molecular composition of NOCs in both pre-fog aerosols and fog water collected at a suburban site in northern China was characterized using Fourier-transform ion cyclotron resonance mass spectrometry in both negative and positive modes of electrospray ionization (ESI- and ESI+). In both pre-fog aerosols and fog water, NOCs account for number fractions of more than 60 % in all assigned formulas in ESI- mode and more than 80 % in ESI+ mode. By comparing the molecular composition of biomass burning, coal combustion, and vehicle emissions, 72.3 % of NOCs in pre-fog aerosols were assigned as originating from these primary anthropogenic sources (pNOCs), while the remaining NOCs were regarded as secondary NOCs formed in aerosol (saNOCs). On the other hand, the unique NOCs in fog water were regarded as secondary NOCs formed in fog (sfNOCs). According to “precursor-product pair” screening involving 39 reaction pathways, we found that the nitration reaction, the amine pathway and the intramolecular N-heterocycle pathway of NH3 addition reactions contribute to 43.6 %, 22.1 %, and 11.6 % of saNOCs, but 26.8 %, 28.4 %, and 29.7 % of sfNOCs, respectively. Such distinct formation pathways are most likely attributed to the diverse precursors and the aqueous acidity. Correspondingly, saNOCs contain more abundant carbohydrates-like and highly oxygenated compounds with two nitrogen atoms compared to pNOCs, whereas sfNOCs contain more lipids-like with fewer oxygen atoms. The results reveal the disparity in secondary processes that contribute to the richness of NOCs in aerosols and fog water. The findings are valuable for understanding the formation and control of organic nitrogen pollution. [ABSTRACT FROM AUTHOR]

Organosulfur compounds (OrgSs), especially organosulfates, have been widely reported at large quantities in particulate organic matter found in various atmospheric environments. Despite various kinds of organosulfates and their formation mechanisms being previously identified, a large fraction of OrgSs remain unexplained at the molecular level, impeding further knowledge on additional formation pathways and critical environmental parameters that help to explain their concentrations. In this work, the abundance and molecular composition of OrgSs in fine particulate samples collected in Guangzhou was reported. Our results revealed that organic sulfur can averagely contribute to 30% of total particulate sulfur, and showed positively correlations with the SO2 (푟=0.37, 푡<0.05) and oxidants (NOx+O3, 푟=0.40, 푝<0.01). Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) results presented that more than 80% by number of the detected OrgSs in our samples have the elemental composition of O/(4S+3N) =1, indicating that they were largely in the form of oxidized organosulfates and/or nitrooxy organosulfates . Many OrgSs, which are tentatively attributed to previously identified biogenic and anthropogenic origins, were also present in aerosols derived from freshly-emitted combustion sources. Results show that the formation of OrgSs through an epoxide intermediate pathway could be as much as 46%, and the oxidants levels could explain 20% variation of organic sulfur mass. The analysis from our large FT-ICR MS dataset suggests that relative humidity, oxidation of biogenic volatile organic compounds via ozonolysis, and NOx-related nitrooxy organosulfate formations were the major reasons for the molecular variation of OrgSs, possibly highlighting the importance of heterogeneous reactions involving either the uptake of SO2 or the heterogeneous oxidations of particulate organosulfates into additional unrecognized OrgSs. [ABSTRACT FROM AUTHOR]

Unlike the deep understanding of highly oxygenated organic molecules (HOMs) driving continental new particle formation (NPF), little is known about the organics involved in coastal and open ocean NPF. On the coastline of China we observed intense coastal NPF events initiated by iodine nucleation, but particle growth to cloud condensation nuclei (CCN) sizes was dominated by organic compounds. This article revealed a new group of C18,30HhOoNn and C20,24,28,33HhOo compounds with specific double bond equivalents and oxygen atom numbers in sub-20 nm coastal iodine new particles by using ultrahigh resolution Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR-MS). We proposed these compounds are oxygenated or nitrated products of long chain unsaturated fatty acids, fatty alcohols, non-protein amino acids or amino alcohols emitted mutually with iodine from coastal biota or biological-active sea surface. Group contribution method estimated that the addition of -ONO2, -OH and -C = O groups to the precursors reduced their volatility of by 2~7 orders of magnitude and thus made their products condensable onto iodine new particles in the coastal atmosphere. Non-target MS analysis also provided a list of 440 formulas of iodinated organic compounds in size-resolved aerosol samples during the iodine NPF days, which facilitates the understanding of unknown aerosol chemistry of iodine. [ABSTRACT FROM AUTHOR]

The physical evolution (metamorphism) of snow is known to affect the chemical composition of dissolved organic matter (DOM) within it. Here, we present a comprehensive study on the Dongkemadi glacier in the central Tibetan Plateau by analyzing surface snow/ice samples collected from May to October 2015. Based on their physical descriptions, these samples were grouped into four categories, i.e., fresh snow, fine firn, coarse firn, and granular ice that represented the different stages of snowmelt. The concentrations of dissolved organic carbon (DOC) decreased from fresh snow (26.8μmolL-1) to fine firn (15.0μmolL-1) and then increased from fine firn to coarse firn (26.1μmolL-1) and granular ice (34.4μmolL-1). This reflected the dynamic variations in DOC observed during snowmelt. The use of excitation emission matrix fluorescence with parallel factor analysis (EEM-PARAFAC) identified three protein-like components (C1, C2 and C4) and one microbial humic-like component (C3), which reflected the presence of significant amounts of microbially derived DOM in surface snow/ice. The molecular level compositions of DOM identified using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) also showed the presence of molecules that were newly produced during snowmelt. These results suggest that snowmelt not only induced a loss of DOM but also intensified the in situ microbial activities that enriched and modified it. These findings are important for understanding the evolution of the physical and chemical characteristics of DOM during the ablation season and can also shed some light on the nature of biogeochemical cycles in cryospheric regions. [ABSTRACT FROM AUTHOR]