Optimizing a multimedia model to assess the differential roles of crops and natural vegetation in the fate of PAHs.

Vegetation plays an important role in the environmental transport behavior of organic pollutants, however, the different roles of crops and natural vegetation have been ignored in most previous studies. In this study, we developed the BETR-Urban-Rural-Veg model to quantitatively evaluate the influences of both natural vegetation and crops on the multimedia transport processes of Phenanthrene (PHE) and Benzo(a)pyrene (BaP) in mainland of China. The geographic distribution of polycyclic aromatic hydrocarbon (PAH) emissions and concentrations were consistent, displaying higher levels in northern China while lower levels in southern China. Under seasonal simulations, for both natural vegetation and crops, PAH concentrations in winter and spring were 1.5 to 27-fold higher than in summer and autumn, especially for PHE. Owing to the higher leaf area index (LAI) of natural vegetation and harvesting of crops, the filter and sequestration effect of natural vegetation was stronger than crops, while the seasonal changes of PAH concentrations in crops were more significant than natural vegetation. Temperature, precipitation rates and LAI might have important influences on seasonal concentrations and overall persistence of PAHs. PHE was more sensitive to the impacts of seasonal environmental parameters. Under different landscape scenarios, average annual PAH concentrations in natural vegetation were always a little higher than those in crops, and the overall persistence of BaP was greatly affected increasing by 15.15 %-16.47 %. This improved model provides a useful tool for environmental management. The results of this study are expected to support land use plans and decision-making in mainland China.