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| Titel |
Summertime photochemistry during CAREBeijing-2007: ROx budgets and O3 formation |
| VerfasserIn |
Z. Liu, Y. Wang, D. Gu, C. Zhao, L. G. Huey, R. Stickel, J. Liao, M. Shao, T. Zhu, L. Zeng, A. Amoroso, F. Costabile, C.-C. Chang, S.-C. Liu |
| 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 ; 12, no. 16 ; Nr. 12, no. 16 (2012-08-28), S.7737-7752 |
| Datensatznummer |
250011414
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| Publikation (Nr.) |
 copernicus.org/acp-12-7737-2012.pdf |
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| Zusammenfassung |
| We analyze summertime photochemistry near the surface in Beijing, China,
using a 1-D photochemical model (Regional chEmical and trAnsport Model,
REAM-1D) constrained by in situ observations, focusing on the budgets of
ROx (OH + HO2 + RO2) radicals and O3 formation.
While the modeling analysis focuses on near-surface photochemical budgets,
the implications for the budget of O3 in the planetary boundary layer
are also discussed. In terms of daytime average, the total ROx
primary production rate near the surface in Beijing is 6.6 ppbv per hour
(ppbv h−1, among the highest found in urban atmospheres. The largest
primary ROx source in Beijing is photolysis of oxygenated volatile
organic compounds (OVOCs), which produces HO2 and RO2 at
2.5 ppbv h−1 and 1.7 ppbv h−1, respectively. Photolysis of
excess HONO from an unknown heterogeneous source is the predominant primary
OH source at 2.2 ppbv h−1, much larger than that of O1D+H2O
(0.4 ppbv h−1). The largest ROx sink is via OH + NO2
reaction (1.6 ppbv h−1), followed by formation of RO2NO2
(1.0 ppbv h−1) and RONO2 (0.7 ppbv h−1). Due to the large
aerosol surface area, aerosol uptake of HO2 appears to be another
important radical sink, although the estimate of its magnitude is highly
variable depending on the uptake coefficient value used. The daytime average
O3 production and loss rates near the surface are 32 ppbv h−1 and
6.2 ppbv h−1, respectively. Assuming NO2 to be the source of
excess HONO, the NO2 to HONO transformation leads to considerable
O3 loss and reduction of its lifetime. Our observation-constrained
modeling analysis suggests that oxidation of VOCs (especially aromatics) and
heterogeneous reactions (e.g. HONO formation and aerosol uptake HO2)
play potentially critical roles in the primary radical budget and O3
formation in Beijing. One important ramification is that O3 production
is neither NOx nor VOC limited, but in a transition regime where
reduction of either NOx or VOCs could result in reduction of
O3 production. The transition regime implies more flexibility in the
O3 control strategies than a binary system of either NOx or
VOC limited regime. The co-benefit of concurrent reduction of both NOx
and VOCs in reducing column O3 production integrated in the
planetary boundary layer is significant. Further research on the spatial
extent of the transition regime over the polluted eastern China is critically
important for controlling regional O3 pollution. |
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