Assessments of seasonal trend, gas–particle partitioning and deposition flux of polycyclic aromatic hydrocarbons at a semi-rural site

Abstract

Air samples were collected at a semi-rural area between February 2013 and February 2014 to determine the concentrations and gas/particle partitionings of polycyclic aromatic hydrocarbons (PAHs). The sampling was done with a high volume air sampler to cover four seasons and 40 samples were taken. Each sample period was about 24 h. The gas–particle partition coefficients (Kp) of PAHs were calculated and correlated with their subcooled liquid vapor pressures (P0L). The determined slopes (mL) varying from –0.59 to –0.28 were far from the theoretical value (–1) due to the absorption, the dominant mechanism. Experimentally determined Kp values were compared with the results obtained using the octanol–air and soot–octanol partitioning models. An octanol-based absorptive partitioning model resulted in a better prediction than the soot–octanol based partitioning model. The total (gas + particle) PAH concentrations changed between 6 and 798 ng m−3 with an average of 205 ± 236 ng m−3. According to Clausius–Clapeyron equation, the local PAH sources were effective. The diagnostic ratios indicated that coal and wood-burning, and traffic emissions were the dominant PAH sources. Dry deposition fluxes for gas and particle phase were also estimated using documented dry deposition velocities and mass transfer coefficients in the literature and concentrations measured in this study.