Volatile organic compounds measured in summer in Beijing and their role in ground‐level ozone formation

Abstract

[1] Beijing has long suffered from serious ground-level ozone pollution, and volatile organic compounds (VOCs) play a key role in ozone formation. To understand the chemical speciation of VOCs in Beijing, nonmethane hydrocarbons (NMHCs) and oxygenated VOCs (OVOCs) were measured in summer in Beijing and nearby provinces (VOCs in this work means NMHCs+OVOCs). A variation of VOC mixing ratios and chemical speciation from 2004 to 2006 was observed at an urban site in Beijing. The typical VOC species, e.g., propane, propene, and toluene, had comparable or lower mixing ratios than levels found in other cities that previously hosted the Olympic Games, while the mixing ratios for isoprene were higher. The chemical compositions of VOCs within Beijing were heavily influenced by vehicular emissions and differed from those obtained in Tianjin and Hebei Province. OVOCs were an important component, accounting for 54% and 37% in the VOC mixing ratio in 2005 and 2006, respectively, and about 40% of the OH loss rates. The main reactive VOC compounds were aldehydes and alkenes. By using isoprene chemistry and the ratio of ethylbenzene to mp-xylene, the initial mixing ratios of VOCs were estimated. The VOCs had similar variation patterns to ambient ozone and peroxyacetyl nitrate (PAN) concentrations. The correlation between daily maximum ozone concentrations and initial VOCs revealed that ozone formation was sensitive to VOCs for both urban (Peking University, PKU) and rural (Yufa) sites. A reduction in NO x would lead to a decrease in ozone at Yufa, but would cause increased ozone at the PKU site.

The impact of speciated VOCs on regional ozone increment derived from measurements at the UK EMEP supersites between 1999 and 2012

“…However, the "state" of atmospheric composition variation producing a regional O 3 increment above hemispheric background concentrations is more rigorously evaluated by considering the chemical loss of the measured VOCs, since it is the VOC chemical loss in the air mass that drives the production of a regional O 3 increment, not the VOC concentration remaining in the air mass. In urban environments, the chemical loss of VOCs has been calculated through the estimation of initial emission ratios of two VOCs and calculation of photochemical age through parameters such as "OH exposure" or "VOC consumption" (Shao et al, 2009;Yuan et al, 2012). This method is not appropriate for rural studies since it assumes that local sources dominate emissions.…”

Seasonal and diurnal variations of atmospheric peroxyacetyl nitrate, peroxypropionyl nitrate, and carbon tetrachloride in Beijing

“…Beijing, the capital of China, is suffering from serious photo-oxidants pollution as indicated by elevation of O 3 (Gao and Zhang, 2012;Shao et al, 2009;Tang et al, 2009;Wang et al, 2006;Zhang et al, 2004). However, the measurements of PANs as the indicator of photochemical pollution, in the megacity are relatively sparse (Wang and Zhang, 2007;Yang et al, 2009;Zhang et al, 2011), and the existing studies mostly carried out over short period during summer, generally a few weeks.…”

Sources of C2–C4 alkenes, the most important ozone nonmethane hydrocarbon precursors in the Pearl River Delta region

“…Although Shao et al (2009) attempted to restore initial ratios to indicate sources of VOCs, there still existed large uncertainties since an individual VOC species in ambient air may vary greatly in where and when it was emitted to the atmosphere. Some paired VOCs, like trans-2-butene/cis-2-butene and m,p-xylenes/ethylbenzene, share common sources but have different atmospheric lifetimes, so their slopes are frequently used as indicators of chemical aging Yuan et al, 2012;Y.J.…”

“…A recent study by Liu et al (2012), with a comprehensive photochemical modeling analysis based on measurements in Beijing, demonstrated that ozone production might be in a transition regime where it is sensitive to both VOC and NO x emissions. As for the PRD region, previous studies revealed that ground-level ozone production was sensitive to VOC emissions (Zhang et al, 2007;Shao et al, 2009;Cheng et al, 2010), and aromatic hydrocarbons (AHs) and alkenes were the critical VOC groups contributing to ozone formation (Tang et al, 2007;Zhang et al, 2007;Cheng et al, 2010;Y.L. Zhang et al, 2012).…”