Molecular Tracers, Mass Spectral Tracers and Oxidation of Organic Aerosols Emitted from Cooking and Fossil Fuel Burning Sources

Abstract

Secondary organic aerosol (SOA) composes a substantial fraction of atmospheric particles, yet the formation and aging mechanism of SOA remains unclear. Here we investigate the initial oxidation of primary organic aerosol (POA) and further aging of SOA in winter Beijing by using aerosol mass spectrometer (AMS) measurements along with offline molecular tracer analysis. ME-2 source apportionment was conducted to capture the characteristic of source-related SOA, and connect them with specific POA. Our results show that urban cooking and fossil fuel burning sources contribute significantly (17% and 20%) to total organic aerosol (OA) in winter Beijing. Molecular tracer analysis by GC×GC reveals that cooking SOA (CSOA) is produced through both photooxidation and aqueous-phase processing, while less oxidized SOA (LO-SOA) is the photooxidation product of fossil fuel burning OA (FFOA) and may experience aqueous-phase aging to form more-oxidized oxygenated OA (MO-OOA). Furthermore, C 3 HO 2 + and C 4 H 5 O 2 + are mass spectral tracers indicating the initial photooxidation, while CH 2 O + and C 2 H 2 O 2 + imply further aqueous-phase aging of OA. Tracer analysis indicates that the formation of diketones dominates the initial photooxidation of POA, while the formation of glyoxal and diacids dominates the further aqueous-phase aging of SOA.

Keywords: secondary organic aerosol, AMS, ME-2 analysis, photooxidation, aqueous-phase processing