Microscale spatial distribution and health assessment of PM_2.5-bound polycyclic aromatic hydrocarbons (PAHs) at nine communities in Xi'an, China

Spatial variability of polycyclic aromatic hydrocarbons (PAHs) associated with fine particulate matter (PM_2.5) was investigated in Xi'an, China, in summer of 2013. Sixteen priority PAHs were quantified in 24-h integrated air samples collected simultaneously at nine urban and suburban communities. The total quantified PAHs mass concentrations ranged from 32.4 to 104.7 ng m⁻³, with an average value of 57.1 ± 23.0 ng m⁻³. PAHs were observed higher concentrations at suburban communities (average: 86.3 ng m⁻³) than at urban ones (average: 48.8 ng m⁻³) due to a better enforcement of the pollution control policies at the urban scale, and meanwhile the disorganized management of motor vehicles and massive building constructions in the suburbs. Elevated PAH levels were observed in the industrialized regions (west and northwest of Xi'an) from Kriging interpolation analysis. Satellite-based visual interpretations of land use were also applied for the supporting the spatial distribution of PAHs among the communities. The average benzo[a]pyrene-equivalent toxicity (Σ[BaP]_eq) at the nine communities was 6.9 ± 2.2 ng m⁻³ during the sampling period, showing a generally similar spatial distribution to PAHs levels. On average, the excess inhalation lifetime cancer risk derived from Σ[BaP]_eq indicated that eight persons per million of community residents would develop cancer due to PM_2.5-bound PAHs exposure in Xi'an. The great in-city spatial variability of PAHs confirmed the importance of multiple points sampling to conduct exposure health risk assessment.