Combined effects of temperature and monsoon on seasonal variations of atmospheric polycyclic aromatic hydrocarbons in the coastal Shanghai, China

Abstract

An intensive sampling program was conducted at two coastal sites of megacity Shanghai - the emerging town Lingang New Area (LGNA), and the petrochemical-industry zone Jinshan Area (JSA) from July 2016–June 2017, to study the occurrence, sources, environmental behavior and fate of atmospheric polycyclic aromatic hydrocarbons (PAHs). Results showed the median concentrations of total atmospheric PAHs were 18 ng m−3 and 12 ng m−3 in JSA and LGNA, respectively, which were lower than those recently detected in northern coastal China, and previously detected in urban/suburban Shanghai. There was strong/opposite temperature dependence for gaseous and particle-bound PAHs, indicating the importance of ongoing local and nearby volatilization; While the gas-particle partitions of individual PAH compound changed dramatically with seasons, with most easily adsorbed on particles during colder months. The potential source contribution function (PSCF) and concentration weight trajectory (CWT) model demonstrated the interactions of terrestrial and marine air mass regulated by the East Asian monsoon. Specifically, PAHs released by wintertime coal heating in northern China and summertime marine shipping in East China Sea, that transported through northwest and southeast monsoon, respectively, and aggravated the pollution of coastal Shanghai, especially for the background site in LGNA. The positive matrix factorization (PMF) source apportionment suggested the dominance of petrogenic sources for gaseous PAHs, coal and biomass combustion sources for particle-bound PAHs, and further demonstrated the seasonal variations of these potential sources. Atmospheric PAHs would deposit to the coastal waters, with gaseous absorption fluxes almost an order of magnitude higher than those of particle-bound deposition.