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| Titel |
Impact of isoprene and HONO chemistry on ozone and OVOC formation in a semirural South Korean forest |
| VerfasserIn |
S. Kim, S.-Y. Kim, M. Lee, H. Shim, G. M. Wolfe, A. B. Guenther, A. He, Y. Hong, J. Han |
| 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. 8 ; Nr. 15, no. 8 (2015-04-29), S.4357-4371 |
| Datensatznummer |
250119669
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| Publikation (Nr.) |
 copernicus.org/acp-15-4357-2015.pdf |
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| Zusammenfassung |
| Rapid urbanization and economic development in East Asia in past decades has
led to photochemical air pollution problems such as excess photochemical
ozone and aerosol formation. Asian megacities such as Seoul, Tokyo, Shanghai,
Guangzhou, and Beijing are surrounded by densely forested areas, and recent
research has consistently demonstrated the importance of biogenic volatile
organic compounds (VOCs) from vegetation in determining oxidation capacity in
the suburban Asian megacity regions. Uncertainties in constraining
tropospheric oxidation capacity, dominated by hydroxyl radical, undermine our
ability to assess regional photochemical air pollution problems. We present
an observational data set of CO, NOx, SO2, ozone, HONO, and VOCs
(anthropogenic and biogenic) from Taehwa research forest (TRF) near the Seoul
metropolitan area in early June 2012. The data show that TRF is
influenced both by aged pollution and fresh biogenic volatile organic compound emissions. With the data set,
we diagnose HOx (OH, HO2, and RO2) distributions calculated
using the University of Washington chemical box model (UWCM v2.1) with
near-explicit VOC oxidation mechanisms from MCM v3.2 (Master Chemical
Mechanism). Uncertainty from unconstrained HONO sources and radical recycling
processes highlighted in recent studies is examined using multiple model
simulations with different model constraints. The results suggest that
(1) different model simulation scenarios cause systematic differences in
HOx distributions, especially OH levels (up to 2.5 times), and (2) radical
destruction (HO2 + HO2 or HO2 + RO2) could be
more efficient than radical recycling (RO2 + NO), especially in the
afternoon. Implications of the uncertainties in radical chemistry are
discussed with respect to ozone–VOC–NOx sensitivity and VOC oxidation
product formation rates. Overall, the NOx limited regime is assessed
except for the morning hours (8 a.m. to 12 p.m. local standard time), but the degree of sensitivity can significantly
vary depending on the model scenarios. The model results also suggest that
RO2 levels are positively correlated with oxygenated VOCs (OVOCs)
production that is not routinely constrained by observations. These
unconstrained OVOCs can cause higher-than-expected OH loss rates (missing OH
reactivity) and secondary organic aerosol formation. The series of modeling
experiments constrained by observations strongly urge observational
constraint of the radical pool to enable precise understanding of regional
photochemical pollution problems in the East Asian megacity region. |
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