Modeling the atmospheric transport and outflow of polycyclic aromatic hydrocarbons emitted from China

An Euler atmospheric transport model CanMETOP (Canadian Model for Environmental Transport of Organochlorine Pesticides) was applied to the atmospheric transport and outflow of polycyclic aromatic hydrocarbons (PAHs) in China in 2003 based on a square kilometer resolution emission inventory. The reaction with OH radical, gas/particle partition by considering the adsorption onto total aerosol surface area, and dynamic soil/ocean–air exchange of PAHs were also considered. The results show that the spatial distribution of PAH concentration levels in the atmosphere is greatly controlled by emission and meteorological conditions. Elevated concentration levels are predicted in Shanxi, Guizhou, North China Plain, Sichuan Basin and Chongqing metropolitan areas due to the high emission densities at those locations. High concentrations are also modeled in environments offshore of China and in the western Pacific Ocean. The model also predicts a slightly decreasing vertical profile in the planetary boundary layer (lower than ∼1 km), but concentration decreases ∼2 orders of magnitude in the free atmosphere. The Westerlies as well as the East Asian Monsoon and local topographical forcings are identified as key factors influencing the transport pattern of PAHs in China. In 2003, ∼3800°tons of the sixteen parent PAHs listed on USEPA priority control list were transported out of China with about 80% transported through the eastern boundary. The outflow concentrates near 30°N, signifying a slight discrepancy from the position of emission density peaks. The center of the outflow plume is located at a height of ∼1 km at 120°E, and climbs to 3.5 km and 5 km at 130°E and 140°E, respectively. A seasonal variation of 5–6 fold is also found for the outflow flux with greatly elevated transport flux in spring and winter.