Quantifying New Sources of Ambient Organic Aerosol and Their Roles in Particle Growth Using Oxygenated Organic Molecule (OOM) Tracers

Abstract

China is suffering from frequent PM_2.5 episodes in the winter characterized by rapid particle growth. Organic aerosol (OA) is often the bottleneck of further reducing PM pollution. To devise effective control measures, the sources of OA must be identified and quantified first. This study expanded the capability of cutting-edge iodide-based chemical ionization mass spectrometry in a source apportionment study by measuring a variety of oxygenated organic molecules (OOMs). A workflow was developed to find suitable tracers from these OOMs. The source apportionment research of OAs was advanced by incorporating these OOM tracers with traditional nonpolar/polar organic tracers. The OOMs-incorporated positive matrix factorization (PMF) was applied to two unique groups of aerosol samples collected in an inland megacity and an ocean expedition. PMF without OOM tracers overestimated the OA contribution from fossil fuel combustion, plastic burning, and monoterpene SOA. On average, PMF with OOM tracers assigned 28.8% and 44.1% of OA in inland megacity and marine samples, respectively, to 4 new factors: aliphatic SOA, highly oxidized aromatic SOA, sulfur-containing SOA, and nitrogen-containing SOA. A one-hour resolution measurement found nitrogen-containing SOA and sulfur-containing SOA were significantly enhanced in particles during nighttime and daytime particle growth events, respectively.