Atmospheric polycyclic aromatic hydrocarbon concentrations and gas/particle partitioning at background, rural village and urban sites in the North China Plain

Gas and particle-phase polycyclic aromatic hydrocarbons (PAHs) were measured in air at a background site (Xiaolongmen), two rural village sites (Gubeikou and Donghe), and at an urban site (Beijing) in the North China Plain from September 2007 to August 2008. The annual average total PAH concentration in Donghe was 730.7 ± 608.0 ng/m3 and 18.2, 3.0, and 1.8 times higher than Xiaolongmen, Gubeikou and Beijing, respectively. Gas/particle partitioning coefficients, Kp, were calculated for each PAH and their relationship with the subcooled liquid vapor pressure p0l and octanol–air partition coefficients (Koa) of the PAHs was investigated. At the rural (Gubeikou) and urban (Beijing) sites, the regression slopes of log Kp versus log p0l were much steeper than −1, indicating that adsorption of PAHs to particulate matter dominated over absorption possibly because, at these sites, the freshly emitted particulate matter and PAHs had not yet reached equilibrium. However, gas/particle partitioning of PAHs approached equilibrium at the background site (Xiaolongmen) because of long-range transport and longer transport times of the PAHs. In addition, the partitioning between the gas and particle phases was studied according to three different models: the Junge–Pankow adsorption model, the Koa absorption model, and the dual organic matter absorption model combined with the soot carbon adsorption model. The Junge–Pankow model and Koa model both under-predicted our experimental Kp values. However, the dual model fit our experimental Kp values well. This suggests that PAH adsorption onto soot carbon and absorption into organic matter were both important for PAH gas/particle partitioning in the North China Plain.