Implications of seasonal control of PM 2.5 -bound PAHs: An integrated approach for source apportionment, source region identification and health risk assessment.

PM _2.5 -bound PAHs are ubiquitous in urban atmospheres and are characterized as carcinogenic, teratogenic and mutagenic upon inhalation. A total of 218 daily PM _2.5 samples were collected during one year in the urban district of Beijing, China. Analysis showed that the annual mean concentration of total PAHs (TPAHs) was 66.2 ng/m ³ , with benzo(a)pyrene (BaP) accounting for 12.4%. High-molecular-weight (HMW, 4-6 rings) PAHs were the dominant components. Seasonal TPAH concentrations decreased in the order of heating season (156 ng/m ³ ) > autumn (20.4 ng/m ³ ) > spring (16.0 ng/m ³ ) > summer (12.5 ng/m ³ ) and were related to meteorological conditions and source emission intensity. The source-attributed mass contribution and source regions of three sources (i.e., (1) vehicle emissions; (2) coal combustion; and (3) petroleum volatilization, natural gas and biomass combustion) were identified by integrating the positive matrix factorization (PMF), potential source contribution function (PSCF) and conditional probability function (CPF). Vehicle emissions contributed the most mass (54.6%), followed by coal combustion (29.8%), on an annual basis. Combined with actual regional emissions, vehicle emissions were mainly derived from local sources, while coal combustion mainly came from regional transport from surrounding areas. Vehicle emissions and coal combustion have much higher mass contributions in the heating season. The source-attributed cancer risk was further evaluated based on source mass contribution and inhalation unit risk. Vehicle emissions contributed the largest risk (2.8 × 10 ^-6 , accounting for 71%) as a result of 30 years of exposure for local residents, exceeding the acceptable level (10 ^-6 ). The heating season showed the most risk, especially in response to vehicle emissions and coal combustion. Overall, the source-attributed cancer risk was regarded as the better index for the development of a control strategy of PM _2.5 -bound PAHs for protecting residents. Based on this index, priority control sources in each season were identified to supply a more effective management solution.
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