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| Titel |
Impact of pollution controls in Beijing on atmospheric oxygenated volatile organic compounds (OVOCs) during the 2008 Olympic Games: observation and modeling implications |
| VerfasserIn |
Y. Liu, B. Yuan, X. Li, M. Shao, S. Lu, Y. Li, C.-C. Chang, Z. Wang, W. Hu, X. Huang, L. He, L. Zeng, M. Hu, T. Zhu |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 15, no. 6 ; Nr. 15, no. 6 (2015-03-18), S.3045-3062 |
| Datensatznummer |
250119557
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| Publikation (Nr.) |
 copernicus.org/acp-15-3045-2015.pdf |
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| Zusammenfassung |
| 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. |
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