The impacts of pollution control measures on PM2.5 reduction: Insights of chemical composition, source variation and health risk

To understand the impact of pollution control measures on the ambient fine particle (PM2.5) in Nanjing, two sampling campaigns before and after the release of pollution control measures (BPCM: Jan.–Nov. 2014 and APCM: Nov. 2015–Jul. 2016) were conducted. Chemical compositions, sources, regional transport, and potential health risks of PM2.5 for the two distinguishable periods were compared. Results showed that the annual averaged PM2.5 concentrations in Nanjing decreased by 12.4% from BPCM (100 ± 54.3 μg m−3) to APCM (87.6 ± 56.4 μg m−3). Chemical mass closure showed that secondary inorganic aerosols (SIA) contributed most to the PM2.5 mass (50.7% and 47.1% for BPCM and APCM), followed by carbonaceous components (30.8% and 33.8%) for both the two periods. Positive matrix factorization (PMF) modeling showed that the annual average mass contributions of biomass burning (BB), industrial process (IP), vehicle emission (VE), and secondary inorganic aerosol (SIA) decreased by 5.60%, 60.9%, 22.0% and 35.8%, respectively, from BPCM to APCM, whereas the contribution of coal combustion (CC) increased by 94.1% due to the significant increase in winter. Combined with the PMF, Hybrid Single Particle Lagrange Trajectory (HYSPLIT), potential source contribution function (PSCF), concentration-weighted trajectory (CWT), and cluster analysis results, the regional transport of the five identified sources in different periods were obtained. The regional transport of BB, IP, VE and SIA decreased by 50.9%, 82.9%, 10.5%, and 23.4%, respectively from BPCM to APCM, while the CC increased by 131% from BPCM to APCM. Health risk assessment showed that the non-carcinogenic risk and carcinogenic risk of PM2.5-bound heavy metals decreased by 50.0% and 58.3%, respectively. These results indicated that the PM2.5 pollution control measures were effective in Nanjing, for both reducing the mass concentrations and health risks of PM2.5. Further attention should be paid to the reduction of the secondary inorganic aerosols and industrial process, due to their high contribution to PM2.5 mass and health risks. This study also highlighted the impact of regional transport of coal combustion emission from north China on south cities, which should be controlled more strictly especially in winter of China.