Size-segregated emission factors and health risks of PAHs from residential coal flaming/smoldering combustion.

Residential coal combustion is one of the main sources of ambient polycyclic aromatic hydrocarbons (PAHs). Updating its emission estimation is limited by the shortages of emission factors, especially for them in different particle sizes and from different combustion conditions. PAH emission factors (EFs) for nine size-segregated particle segments emitted from smoldering and flaming combustion of residential coals (four kinds of raw coals (RCs) and three kinds of honeycomb coal briquettes (HCBs)) were obtained in China, using a dilution sampling system. EFs of PAHs for the flaming and smoldering of HCB ranged from 1.32 to 2.04 mg kg and 0.35 to 5.36 mg kg, respectively. The EFs of PAHs for RC flaming combustion varied from 0.50 to 218.96 mg kg. About 53.5-96.4% and 47.4-90.9% of PAHs concentrated in PM and PM, respectively. Different fuel types and combustion conditions strongly affected the PAH EFs. The PAH EF for the RC was 0.3 times that for HCB in Guizhou, which implied that PAH EFs for RC combustion were not always higher than those from HCB burning. For different combustion conditions, the PAH EFs from flaming were more than 2.5 times higher than those from smoldering for HCB except in the Anhui region. Results indicated that current PAH EFs may not be universal, which may bias the establishment of control policies for toxic pollutants emitted from domestic coal burning. On average, 73.2 ± 15.5% of total PAH potential toxicity risks were concentrated in submicron particles. More size-segregated PAH EFs for residential coal combustion should be investigated considering combustion conditions with a uniform sampling method in China.