Atmospheric deposition of Polycyclic Aromatic Hydrocarbons (PAHs) to a coastal site of Hong Kong, South China

Abstract

Dry and wet deposition of atmospheric particles is a dominant pathway for PAHs to the coastal environments. Very few studies have been conducted to quantify the contribution of atmospheric deposition to PAH levels in the coastal regions. In this study, PAHs were analyzed in samples collected during a year-round campaign using atmospheric (gas and particle) and depositional samples at a coastal site South China. The average PAH particle deposition fluxes observed calculated 260 ± 190 ng m-2 d-1. Remarkable seasonal variations were recorded in the total PAH deposition fluxes, with higher deposition fluxes in the dry seasons and lower fluxes in the wet seasons. The temporal trend of deposition fluxes was influenced by PAH concentration in the aerosols and changes in meteorological parameters, such as temperature, rainfall, and wind speed etc. Dry deposition velocities of individual PAH compound ranged from 0.02 to 1.03 cm s-1, and there was a decrease pattern in dry deposition velocity with increasing molecular weight of PAHs. The annual mean washout ratio, defined as the ratio between the particle-associated concentrations of PAHs in precipitations and aerosols, was 3.4 × 105 in this study. Washout ratios decreased with increasing rainfall frequency and reached a consistent level afterward. The contribution of atmospheric deposition to PAH concentrations in the sediments was estimated to be 30%-40% in the coastal regions of South China.