Abstract
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.
Highlights
Volatile organic compounds (VOCs) are precursors of tropospheric ozone and secondary organic aerosols (SOAs) (Forstner et al, 1997; Odum et al, 1997; Atkinson, 2000; O’Dowd et al, 2002; Sato et al, 2010)
The results suggest that emission control in the industry and traffic sectors is more effective in lowering ambient reactive VOCs in non-heating seasons; 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
Our measurements at a rural site in this study and the measurements at an urban site by Li et al (2015) consistently demonstrated that the temporary emission controls resulted in a large decrease in ambient VOCs during the AsianPacific Economic Cooperation (APEC) summit, with a more than 30 % reduction in urban areas (Li et al, 2015) and an approximately 50 % reduction in rural areas, as observed in this study
Summary
Volatile organic compounds (VOCs) are precursors of tropospheric ozone and secondary organic aerosols (SOAs) (Forstner et al, 1997; Odum et al, 1997; Atkinson, 2000; O’Dowd et al, 2002; Sato et al, 2010). As ozone formation in urban areas is largely VOC limited (Shao et al, 2009; Tang et al, 2010) and SOAs are important components of fine particles or PM2.5 (particulate matter with an aerodynamic diameter less than 2.5 μm) (Cabada et al, 2004; Lonati et al, 2005; Huang et al, 2014), reducing emissions of VOCs would be very important for improving the air quality in megacities, such as China’s capital city Beijing, where air pollution has become a widespread concern, with increasing surface ozone levels during summer and severe PM2.5 pollution during winter (Streets et al, 2007; Ji et al, 2012; Wang et al, 2014). In residential areas of Izmir, Turkey, for example, household burning of coal on uncontrolled burners for domestic heating during winter was found to be a larger source of VOCs than the local traffic (Sari and Bayram, 2014)
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