Impact of pollution controls in Beijing on atmospheric oxygenated volatile organic compounds (OVOCs) during the 2008 Olympic Games: observation and modeling implications

Abstract

Abstract. Oxygenated volatile organic compounds (OVOCs) are important products of the photo-oxidation of hydrocarbons. They influence the oxidizing capacity and the ozone-forming potential of the atmosphere. In the summer of 2008, 2 months of emission restrictions were enforced in Beijing to improve air quality during the Olympic Games. Observational evidence reported in related studies that these control measures were efficient in reducing the concentrations of primary anthropogenic pollutants (CO, NOx and non-methane hydrocarbons, i.e., NMHCs) by 30–40%. In this study, the influence of the emission restrictions on ambient levels of OVOCs was explored using a neural network analysis with consideration of meteorological conditions. Statistically significant reductions in formaldehyde (HCHO), acetaldehyde (CH3CHO), methyl ethyl ketone (MEK) and methanol were found to be 12.9, 15.8, 17.1 and 19.6%, respectively, when the restrictions were in place. The effect of emission controls on acetone was not detected in neural network simulations, probably due to pollution transport from surrounding areas outside Beijing. Although the ambient levels of most NMHCs were reduced by ~35% during the full control period, the emission ratios of reactive alkenes and aromatics closely related to automobile sources did not present much difference (< 30%). A zero-dimensional box model based on the Master Chemical Mechanism version 3.2 (MCM3.2) was applied to evaluate how OVOC production responds to the reduced precursors during the emissions control period. On average, secondary HCHO was produced from the oxidation of anthropogenic alkenes (54%), isoprene (30%) and aromatics (15%). The importance of biogenic sources for the total HCHO formation was almost on par with that of anthropogenic alkenes during the daytime. Anthropogenic alkenes and alkanes dominated the photochemical production of other OVOCs such as acetaldehyde, acetone and MEK. The relative changes of modeled HCHO, CH3CHO, methyl vinyl ketone and methacrolein (MVK + MACR) before and during the pollution controlled period were comparable to the estimated reductions in the neural network, reflecting that current mechanisms can largely explain secondary production of those species under urban conditions. However, it is worth noting that the box model overestimated the measured concentrations of aldehydes by a factor of 1.4–1.7 without consideration of loss of aldehydes on aerosols, and simulated MEK was in good agreement with the measurements when primary sources were taken into consideration. These results suggest that the understanding of the OVOCs budget in the box model remains incomplete, and that there is still considerable uncertainty in particular missing sinks (unknown chemical and physical processes) for aldehydes and absence of direct emissions for ketones.

Observations and Explicit Modeling of Summertime Carbonyl Formation in Beijing: Identification of Key Precursor Species and Their Impact on Atmospheric Oxidation Chemistry

“…This suggests that reducing anthropogenic emissions of C 2 H 4 would reduce the HCHO pollution. In comparison, for CH 3 CHO, propene (C 3 H 6 ), i-butene, cis-2-pentene, and i-pentane showed the highest RIR values, which is consistent with previous results suggesting that alkenes and alkanes were the main precursors of CH 3 CHO at an urban site in Beijing (Liu et al, 2015). In terms of CHOCHO, in addition to C 5 H 8 showing the highest RIR, anthropogenic aromatics, especially toluene, also presented a significant contribution.…”

Sources and Potential Photochemical Roles of Formaldehyde in an Urban Atmosphere in South China

“…Factor 3 is highly loaded with isoprene, monoterpene, and MVK + MACR; all of these species are mostly natural emissions and degradation products (MVK + MACR) (Rinne et al, 2002). It has been reported that isoprene is the major precursor of HCHO, and its contribution to the total HCHO formation was 80-90% in summer in the Southeast U.S. (Marvin et al, 2017;Wolfe et al, 2016), 44% in New York City (Lin et al, 2012), and 30% in Beijing (Liu et al, 2015). Therefore, Factor 3 was identified as a biogenic source.…”

Differentiating local and regional sources of Chinese urban air pollution based on the effect of the Spring Festival

“…The toluene / benzene ratio can be used to estimate the contribution of traffic emissions (Schneider et al, 2005). Generally, a value of 1.2-3 is found to be characteristic of vehicular emission in many urban areas (Nelson and Quigley, 1984;Wang et al, 2002;Araizaga et al, 2013). The lower ratio of toluene to benzene (ave. = 2.6) in the SF period suggests that the dominant source is vehicle emission.…”