Source-specific risks of synchronous heavy metals and PAHs in inhalable particles at different pollution levels: Variations and health risks during heavy pollution.

Synchronous heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) in inhalable particulate matter (PM) were measured during 2009-2012 and 2015-2016 in a Chinese megacity (Chengdu) to understand the variations in source-specific health risks during haze episodes. Samples were divided into four mass concentration levels: PM ≤ 150 μg m (L1), 150 μg m < PM ≤ 250 μg m (L2), 250 μg m < PM ≤ 350 μg m (L3), and PM > 350 μg m (L4). The percentages of some HMs and PAHs (accounting for PM) decreased from L1 to L4, indicating that they exhibited lower growth rates than other species during heavy pollution. The combined cancer risk (R) for HMs and PAHs was higher at L1 and L4, and the combined non-cancer risk (HQ) was significantly high at L4. The HMs and PAHs combined source-specific risk apportion (HP-SRA) model was employed to quantify the source-specific risks. The relative contributions of (i) diesel and gasoline vehicles to the R, and (ii) crustal dust to the HQ increased during heavy pollution (L3 and L4). The relative contribution of industrial source declined from 81% (L1) to 60% (L4) for the HQ, and from 49% (L1) to 36% (L4) for the R, implying that the control of industrial emissions during heavy pollution events could alleviate risk growth as a co-benefit of controlling PM mass concentration. However, the risks associated with industrial emissions should also be considered during 'clean' days.