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A vast area in northern China, especially during wintertime, iscurrently suffering from severe haze events due to the high levels ofatmospheric PM2. 5. To recognize the reasons for the high levels ofPM2. 5, daily samples of PM2. 5 were simultaneouslycollected at the four sampling sites of Beijing city (BJ), Baoding city (BD),Wangdu county (WD) and Dongbaituo (DBT) during the winter and spring of2014–2015. The concentrations of the typical water-soluble ions (WSIs, suchas Cl−, NO3−, SO42− and NH4+) at DBTwere found to be remarkably higher than those at BJ in the two winters, butalmost the same as those at BJ in the two springs. The evidently greaterconcentrations of OC, EC and secondary inorganic ions (NO3−,SO42−, NH4+ and Cl−) at DBT than at WD, BD and BJduring the winter of 2015 indicated that the pollutants in the rural areawere not due to transportation from neighbouring cities but dominated bylocal emissions. As the distinct source of atmospheric OC and EC in the ruralarea, the residential coal combustion also made a contribution to secondaryinorganic ions through the emissions of their precursors (NOx,SO2, NH3 and HCl) as well as heterogeneous or multiphasereactions 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 veryclose 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 fullysurrounded by the countryside, were strongly affected by the residential coalcombustion. The OC ∕ EC ratios at the four sampling siteswere almost the same value (4.8) when the concentrations of PM2. 5were greater than 150 µg m−3, suggesting that the residentialcoal combustion could also make a dominant contribution to atmosphericPM2. 5 at BJ during the severe pollution period when the air parcelswere usually from southwest–south regions, where a high density of farmersreside. The evident increase in the number of the species involved insignificant correlations (p < 0. 05) from the countryside to thecities further confirmed that residential coal combustion was thedominant source of key species in the rural area. However, the complexsources including local emissions and regional transportation wereresponsible for the atmospheric species in the cities. Strong correlationsamong OC, EC, Cl−, NO3− and NH4+ were found at thefour sampling sites but only a strong correlation was found between OC (orEC) and SO42− at BJ, implying that the formation rate ofSO42− via heterogeneous or multiphase reactions might berelatively slower than those of NO3−, NH4+ and Cl−.Based on the chemical mass closure (CMC) method, the contributions of theprimary particle emission from residential coal combustion to atmosphericPM2. 5 at BJ, BD, WD and DBT were estimated to be 32, 49, 43 and58 %, respectively

The contribution of residential coal combustion to atmospheric PM&lt;sub&gt;2. 5&lt;/sub&gt; in northern China during winter

The contribution of residential coal combustion to atmospheric PM<sub>2. 5</sub> in northern China during winter