Molecular-level insight into the organic aerosol formation under the interactions between VOCs and inorganic sulfate and NOx

Field observations were conducted in various environments, from polluted urban to clean marine atmospheres, to understand the organic aerosol formation under the influence of inorganic sulfate and NO_x. Molecular compositions of organic aerosols were analyzed using an ultrahigh-resolution mass spectrometer. The S-containing and N-containing organics are important fractions for SOA accumulation during pollution episodes or under high humidity conditions. To further investigate their formation pathways, organosulfates (OSs) and nitro-aromatics (NACs) were quantified using HPLC-MS.

Particulate OSs were formed via acid-catalyzed aqueous-phase reactions in the presence of sulfate aerosols. When sulfate dominated the accumulation of secondary inorganic aerosols, OS formation would be obviously promoted as the increasing of acidic sulfate aerosols, aerosol liquid water and acidity. The formation of biogenic OSs and their notable roles in organic aerosols calls for elaboration in regions with substantial biogenic-anthropogenic interactions and over marine areas with high biological activity and high SST.

Anthropogenic NO_x influences the SOA formation via nighttime NO₃-initiated oxidation of monoterpene, as well as involving in the oxidation of toluene and benzene. As the increasing of NO_x concentration levels, the formation of nitrooxy-OSs or NACs shift from NO_x-limited to NO_x-excess regimes. Transported anthropogenic NO_x from continental outflows would obviously enhance the nitrooxy-OSs formation in organic aerosols over marginal seas.