Seasonal variations, gas-PM2.5 partitioning and long-distance input of PM2.5-bound and gas-phase polycyclic aromatic hydrocarbons in Shanghai, China

Abstract

The sources of PAHs in the urban atmosphere are particularly complex. This study focused on the local emissions and long-distance input of PAHs in the urban atmosphere, which will contribute to the reduction of air pollution. PM2.5-bound and gas-phase concentrations of 16 atmospheric polycyclic aromatic hydrocarbons (PAHs) were investigated during different seasons in Shanghai. The results showed that total concentration of 16 PAHs ranged from 3.19 to 22.26 ng m−3 and 6.13–53.97 ng m−3 in PM2.5 and gas phase, respectively. The seasonal variation is in the following orders: winter > autumn > spring > summer for PM2.5-bound PAHs and winter > summer > autumn > spring for gas-phase PAHs, respectively. The result of gas-particle partitioning between PM2.5 and gas phase indicated that PAHs were most easily adsorbed in particles in autumn. Concentrations of other major air pollutants (PM2.5, SO2, NO2, and CO) had a significant positive correlation with the PM2.5-phase PAHs suggesting both local and regional coal combustion emissions were one of the important sources. Positive Matrix Factorization (PMF) was applied to identify the sources of atmospheric PAHs. It was found that the PM2.5-bound PAHs in Shanghai were mainly from coke and coal combustion (38.71%), traffic emission (23.55%) and biomass combustion (20.98%). However, the sources of gas-phase PAHs were biomass combustion/petroleum combustion and leakage (45.96%), natural gas combustion (29.98%), coke and coal combustion (24.06%). Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLT) showed that Shanghai was more susceptible to atmospheric pollutants from the north of China in spring and winter. The results of Potential Source Contribution Function (PSCF) and Concentration Weighted Trajectory (CWT) indicated that gas-phase PAHs in Shanghai were greatly affected by long-distance input, while the potential source area of PM2.5-bound PAHs mainly distributed in the local and surrounding industrial areas of Shanghai.