Articles | Volume 17, issue 18
Research article
27 Sep 2017
Research article |  | 27 Sep 2017

The contribution of residential coal combustion to atmospheric PM2. 5 in northern China during winter

Pengfei Liu, Chenglong Zhang, Chaoyang Xue, Yujing Mu, Junfeng Liu, Yuanyuan Zhang, Di Tian, Can Ye, Hongxing Zhang, and Jian Guan

Abstract. A vast area in northern China, especially during wintertime, is currently suffering from severe haze events due to the high levels of atmospheric PM2. 5. To recognize the reasons for the high levels of PM2. 5, daily samples of PM2. 5 were simultaneously collected at the four sampling sites of Beijing city (BJ), Baoding city (BD), Wangdu county (WD) and Dongbaituo (DBT) during the winter and spring of 2014–2015. The concentrations of the typical water-soluble ions (WSIs, such as Cl, NO3, SO42− and NH4+) at DBT were found to be remarkably higher than those at BJ in the two winters, but almost the same as those at BJ in the two springs. The evidently greater concentrations of OC, EC and secondary inorganic ions (NO3, SO42−, NH4+ and Cl) at DBT than at WD, BD and BJ during the winter of 2015 indicated that the pollutants in the rural area were not due to transportation from neighbouring cities but dominated by local emissions. As the distinct source of atmospheric OC and EC in the rural area, the residential coal combustion also made a contribution to secondary inorganic ions through the emissions of their precursors (NOx, SO2, NH3 and HCl) as well as heterogeneous or multiphase reactions on the surface of OC and EC. The average mass proportions of OC, EC, NO3 and SO42− at BD and WD were found to be very close to those at DBT, but were evidently different from those at BJ, implying that the pollutants in the cities of WD and BD, which are fully surrounded by the countryside, were strongly affected by the residential coal combustion. The OC ∕ EC ratios at the four sampling sites were almost the same value (4.8) when the concentrations of PM2. 5 were greater than 150 µg m−3, suggesting that the residential coal combustion could also make a dominant contribution to atmospheric PM2. 5 at BJ during the severe pollution period when the air parcels were usually from southwest–south regions, where a high density of farmers reside. The evident increase in the number of the species involved in significant correlations (p < 0. 05) from the countryside to the cities further confirmed that residential coal combustion was the dominant source of key species in the rural area. However, the complex sources including local emissions and regional transportation were responsible for the atmospheric species in the cities. Strong correlations among OC, EC, Cl, NO3 and NH4+ were found at the four sampling sites but only a strong correlation was found between OC (or EC) and SO42− at BJ, implying that the formation rate of SO42− via heterogeneous or multiphase reactions might be relatively slower than those of NO3, NH4+ and Cl. Based on the chemical mass closure (CMC) method, the contributions of the primary particle emission from residential coal combustion to atmospheric PM2. 5 at BJ, BD, WD and DBT were estimated to be 32, 49, 43 and 58 %, respectively.

Short summary
The North China Plain in winter frequently suffers from severe haze pollution which is mainly ascribed to elevation of PM2. 5. Although the government has performed a series of control measures for major pollution sources, the PM2. 5 levels were still above 1000 ug m-3 in some areas of the Beijing–Tianjin–Hebei region. In this study, we found that residential coal combustion made an evident contribution to PM2. 5 in the region, the contributions of which were estimated to be about 32–58 %.
Final-revised paper