Sources and Health Risks of PM2.5-bound PAHs in a Small City along with the “Clean Heating” Policy

Abstract

Levels, composition, and sources of PM2.5-bound polycyclic aromatic hydrocarbons (PAHs) vary significantly along with the “Clean Heating” (CH) policy in Beijing-Tianjin-Hebei (BTH) region, whereas the PAH characteristics with CH in small cities still remain unclear. A field observation was conducted in Baoding City, a small city within the BTH region, in winter of 2019 covering both the pre-heating season (PHS) and the heating season (HS). From the PHS to the HS, the mean concentrations for both PM2.5 and Σ18PAHs increased from 69.1 to 125.0 µg m–3 and from 8.09 to 26.2 ng m–3 due to the heating activities. The far lower PAHs in this study than those of small cities before CH implementation indicated the CH effectiveness. Higher diagnostic ratios (DRs) of FA/(FA + PY), BaA/(BaA + CHR), and IP/(IP + BgP) in the HS were in agreement with the increased coal/biomass usage. Positive matrix factorization (PMF) demonstrated that biomass/natural-gas burning (BNGB) contributed most to PAHs of 36.9% in the HS, the increased natural gas (NG) usage for heating should be responsible for this contribution due to the policies of biomass-burning prohibition and “Coal to Gas”. Coal combustion (CC) shares increased by 152% in the HS despite the “Coal Banning” project. Again, the medium-molecular-weight PAHs (MMW-PAHs) increased most by 400% in the HS, evidencing the increased impacts of fossil-fuel consumptions. As an indicator for carcinogenic risk, BaP increased from 0.937 in the PHS to 1.29 ng m–3 in the HS. Furthermore, the incremental lifetime cancer risks (ILCR) and BaP equivalent concentrations (BaPeq) increased in the HS. The mean ILCR values of 1.15 × 10–6 for adults in the HS exceeded the threshold of 1 × 10–6, while they were lower than 1 × 10–6 for children in both the PHS and the HS, and adults in the PHS due to the CH positive effects.