Chemical analysis of particulate products of aged 1,3,5-trimethylbenzene secondary organic aerosol in the presence of ammonia

Ammonia (NH3) gas-aging of secondary organic aerosol (SOA) results in the formation of organonitrogen compound is an important class of brown carbon. The particulate products of aged 1,3,5-trimethylbenzene (135-TMB) SOA in the presence of NH3 were measured by UV-Vis spectrophotometer, attenuated total reflectance-Fourier transform infrared (ATR-FTIR), and aerosol laser time-of-flight mass spectrometer (ALTOFMS) in present study. Experimental results indicated that NH3 has significant promotion effect on 135-TMB SOA formation. Organic ammonium salts, such as ammonium methyl glyoxylate, ammonium 3,5-dimethylbenzoate, which are formed from NH3 reactions with gaseous organic acids were detected as the principal particulate products of NH3-aged 135-TMB SOA. 4-methyl-imidazole-2-acetaldehyde, 4-methyl- 1H-imidazole and other imidazole products via the heterogeneous reactions between NH3 and dialdehydes of 135-TMB SOA were newly measured. The formation of imidazole products suggests that some ambient particles contained organonitrogen compounds may be come from this mechanism. The results of this study may provide valuable information for discussing SOA aging mechanisms and new route for NH3 deposition.