Volatile organic compounds at a rural site in Beijing: influence of temporary emission control and wintertime heating
Authors: Yang Weiqiang , Zhang Yanli , Wang Xinming , Li Sheng , Zhu Ming , Yu Qingqing , Li Guanghui , Huang Zhonghui , Zhang Huina , Wu Zhenfeng , Song Wei , Tan Jihua , Shao Min 
Published: August 2018

Abstract. While residential coal/biomass burning might be a major and underappreciated
emission source for PM2.5, especially during winter, it is not
well constrained whether burning solid fuels contributes substantially to
ambient volatile organic compounds (VOCs), which are precursors to secondary
organic aerosols (SOAs) that typically have a higher contribution to
particulate matter during winter haze events. In this study, ambient air
samples were collected in 2014 from 25 October to 31 December at a rural
site on the campus of the University of Chinese Academy of Sciences (UCAS)
in northeastern Beijing for the analysis of VOCs. Since temporary
intervention measures were implemented on 3–12 November to improve the air
quality for the Asian-Pacific Economic Cooperation (APEC) summit held on
5–11 November in Beijing, and wintertime central heating started on 15 November in Beijing after the APEC summit, this sample collection period
provided a good opportunity to study the influence of temporary control
measures and wintertime heating on ambient VOCs. As a result of the
temporary intervention measures implemented during 3–12 November (period
II), 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 to
period I, with the larger decrease in SOA formation potentials attributed to
more effective control over aromatic hydrocarbons mainly from solvent use.
Back trajectory analysis revealed that the average mixing ratios of VOCs in
southerly air masses were 2.3, 2.3 and 2.9 times those in northerly air
masses during periods I, II and III, respectively; all VOC episodes occurred
under the influence of southerly winds, suggesting much stronger emissions
in the southern urbanized regions than in the northern rural areas. Based on
a positive matrix factorization (PMF) receptor model, the altered
contributions from traffic emissions and solvent use could explain 47.9 %
and 37.6 % of the reduction in ambient VOCs, respectively, during period
II relative to period I, indicating that the temporary control measures on
vehicle emissions and solvent use were effective at lowering the ambient
levels of VOCs. Coal/biomass burning, gasoline exhaust and industrial
emissions were among the major sources, and they altogether contributed
60.3 %, 78.6 % and 78.7 % of the VOCs during periods I, II and
III, respectively. Coal/biomass burning, mostly residential coal burning,
became the dominant source, accounting for 45.1 % of the VOCs during the
wintertime heating period, with a specifically lower average contribution
percentage in southerly air masses (38.2 %) than in northerly air masses
(48.8 %). The results suggest that emission control in the industry and
traffic sectors is more effective in lowering ambient reactive VOCs in
non-heating seasons; however, during the winter heating season reducing
emissions from residential burning of solid fuels would be of greater
importance and would have health co-benefits from lowering both indoor and
outdoor air pollution.