Non-polar organic compounds in autumn and winter aerosols in a typical city of eastern China: size distribution and impact of gas-particle partitioning on PM2.5 source apportionment

Aerosol-associated non-polar organic compounds (NPOCs), including 15 polycyclic aromatic hydrocarbons (PAHs), 30 n-alkanes, 2 iso-alkanes, 5 hopanes and 5 steranes, were identified and quantified in PM2.5 samples using the thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS) method. The samples were mainly collected in autumn and winter in a typical city of eastern China. The total concentrations of NPOCs were 31.7-388.7 ngm(-3), and n-alkanes were the most abundant species (67.2 %). The heavy-molecular-weight PAHs (four-and fivering) contributed 67.9% of the total PAHs, and the middle-chain-length n-alkanes (C25-C34) were the most abundant (72.3 %) in n-alkanes. PAHs and n-alkanes were mainly distributed in the 0.56-1.00 mu m fraction, while P (hopanes C steranes) were associated with the 0.32-1.00 mu m fraction, suggesting condensation of combustion products was their important origin. The ratio-ratio plots indicated that NPOCs in the local area were affected by photochemical degradation. To reduce the uncertainty caused by only particle NPOC data for source apportionment, the particle and predicted gaseous-phase NPOCs, incorporated with other PM2.5 compound were used as input data for the positive matrix factorization (PMF) model. Eight factors were extracted for both cases: secondary aerosol formation, vehicle exhaust, industrial emission, coal combustion, biomass burning, ship emission, and dust and light NPOCs. These findings highlight the emissions from different aerosol-associated NPOC origins, which caused different size-specific distributions, photodegradation and gas-particle partitioning, which further affect PM2.5 source apportionment. Considering these effects on organic tracers will help us accurately identify the potential sources of aerosols and then asses the contributions from each source.