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. While residential coal/biomass burning might be a major and underappreciatedemission source for PM 2.5 , especially during winter, it is notwell constrained whether burning solid fuels contributes substantially toambient volatile organic compounds (VOCs), which are precursors to secondaryorganic aerosols (SOAs) that typically have a higher contribution toparticulate matter during winter haze events. In this study, ambient airsamples were collected in 2014 from 25 October to 31 December at a ruralsite on the campus of the University of Chinese Academy of Sciences (UCAS)in northeastern Beijing for the analysis of VOCs. Since temporaryintervention measures were implemented on 3–12 November to improve the airquality for the Asian-Pacific Economic Cooperation (APEC) summit held on5–11 November in Beijing, and wintertime central heating started on 15 November in Beijing after the APEC summit, this sample collection periodprovided a good opportunity to study the influence of temporary controlmeasures and wintertime heating on ambient VOCs. As a result of thetemporary intervention measures implemented during 3–12 November (periodII), the total mixing ratios of non-methane hydrocarbons averaged 11.25 ppb,approximately 50 % lower than the values of 23.41 ppb in period I (25 October–2 November) and 21.71 ppb in period III (13 November–31 December).The ozone and SOA formation potentials decreased by ∼50  %and ∼70  %, respectively, during period II relative toperiod I, with the larger decrease in SOA formation potentials attributed tomore effective control over aromatic hydrocarbons mainly from solvent use.Back trajectory analysis revealed that the average mixing ratios of VOCs insoutherly air masses were 2.3, 2.3 and 2.9 times those in northerly airmasses during periods I, II and III, respectively; all VOC episodes occurredunder the influence of southerly winds, suggesting much stronger emissionsin the southern urbanized regions than in the northern rural areas. Based ona positive matrix factorization (PMF) receptor model, the alteredcontributions from traffic emissions and solvent use could explain 47.9 %and 37.6 % of the reduction in ambient VOCs, respectively, during periodII relative to period I, indicating that the temporary control measures onvehicle emissions and solvent use were effective at lowering the ambientlevels of VOCs. Coal/biomass burning, gasoline exhaust and industrialemissions were among the major sources, and they altogether contributed60.3 %, 78.6 % and 78.7 % of the VOCs during periods I, II andIII, respectively. Coal/biomass burning, mostly residential coal burning,became the dominant source, accounting for 45.1 % of the VOCs during thewintertime heating period, with a specifically lower average contributionpercentage in southerly air masses (38.2 %) than in northerly air masses(48.8 %). The results suggest that emission control in the industry andtraffic sectors is more effective in lowering ambient reactive VOCs innon-heating seasons; however, during the winter heating season reducingemissions from residential burning of solid fuels would be of greaterimportance and would have health co-benefits from lowering both indoor andoutdoor air pollution.

Volatile organic compounds at a rural site in Beijing: influence of temporary emission control and wintertime heating