Non-polar organic compounds in aerosols in a typical city of Eastern China: Size distribution, gas-particle partitioning and tracer for PM2.5 source apportionment

摘要

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 PM samples using thermal desorption–gas chromatography/mass spectrometry (TD-GC/MS) method. The samples were collected in a typical city of Eastern China. The total concentrations of NPOCs were 31.7–388.7&thinsdp;ng m, and n–alkanes were the most abundant species (67.2 %). The heavy molecular weight PAHs (4- and 5-ring) contributed 67.88 % of the total PAHs, and the middle chain length n–alkanes (C25–C34) were the most abundant in n-alkanes. PAHs and n-alkanes were majorly distributed in 0.56–1.00 μm fraction. ∑(hopanes+steranes) were associated with the 0.32–1.00 μm fraction. Analysis showed that 83.0 % of NPOCs were originated from anthropogenic sources, especially pyrogenic sources such as fossil fuel combustion and biomass burning. The ratio–ratio plots indicated that NPOCs in local area were affected by photochemical degradation and emissions from mixed sources. Gas-particle partitioning model showed that the particle-phase fraction (φ) of light molecular weight NPOCs ranged from 2.4 % to 62.5 %, while that of heavy NPOCs accounted for more than 90.0 %. The data based on single particle phase and the data based on gas-particles phases incorporated with other PM compounds were used as input data for positive matrix factorization (PMF) model, respectively. Eight factors were extracted for both cases: secondary aerosol formation, vehicle exhaust, industrial emission, coal combustion, biomass burning, ship emission, dust and light NPOCs. This study provides new information on the profiles of PM-associated NPOCs, size-specific distributions, photodegradation and their gas-particle partitioning. This will help us accurately identify the potential sources of aerosols and then asses the contributions from each source.