Concentrations and origins of nitro-polycyclic aromatic hydrocarbons and oxy-polycyclic aromatic hydrocarbons in ambient air in urban and rural areas in northern China.

Twelve nitro-PAHs (nPAHs) and four oxy-PAHs (oPAHs) were measured in air samples for 12 months at 18 sites in urban settings, rural villages, or rural fields in northern China. The nPAH concentrations were higher in urban areas (1.3 ± 1.3 ng/m(3)), and nPAH/parent PAH ratios were higher (suggesting important contributions from motor vehicles and secondary formation) in urban sites than in rural villages. oPAHs are primarily emitted from solid fuel combustion and motor vehicles, and similar oPAH concentrations were found in urban areas (23 ± 20 ng/m(3)) and rural villages (29 ± 24 ng/m(3)). The high numbers of motor vehicles in Beijing and intensive industrial activity in Taiyuan and Dezhou caused higher nPAH concentrations. No spatial trend in oPAH concentrations was found in the rural villages, because similar oPAH mixtures are emitted from solild fuel combustion. The nPAH and oPAH concentrations were higher in the winter, and correlated with residential energy consumption and precipitation.