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| Titel |
Nitrous acid in a street canyon environment: sources and the contribution to local oxidation capacity |
| VerfasserIn |
Hui Yun, Zhe Wang, Qiaozhi Zha, Weihao Wang, Likun Xue, Li Zhang, Qinyi Li, Long Cui, Shuncheng Lee, Steven Poon, Tao Wang |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250142269
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| Publikation (Nr.) |
 EGU/EGU2017-5869.pdf |
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| Zusammenfassung |
| Nitrous acid (HONO) is one of the dominant sources of hydroxyl radical (OH) and plays an
important role in photochemical oxidation processes in the atmosphere. Even though HONO
has been extensively studied in urban areas, its importance and effects in street canyon
microenvironment has not been thoroughly investigated. Street canyons which suffer serious
air pollution problem are widely distributed in downtown areas with paralleled high buildings
and narrow roads in the center. In this study, we measured HONO at a roadside of a street
canyon in urban Hong Kong and applied an observation-based box model based on
Master Chemical Mechanism (MCM 3.3) to investigate the contribution of HONO
to local oxidation chemistry. Higher HONO mixing ratios were observed in the
daytime than in the nighttime. An average emission ratio (ΔHONO/ΔNOx) of
1.0% (±0.5%) was derived at this roadside site and the direct HONO emission
from vehicles contributed to 38% of the measured HONO in the street canyon.
Heterogeneous NO2 conversion on humid ground or building surfaces and the uptake of
NO2 on fresh soot surfaces were the other two important HONO sources in this
microenvironment. OBM simulations constrained with observed HONO showed that the peak
concentration of OH, HO2 and RO2 is 7.9, 5.0 and 7.5 times of the result in the case
with only OH+NO as HONO source. Photolysis of HONO contributed to 86.5% of
the total primary radical production rates and can lead to efficient NO2 and O3
production under the condition of weak regional O3 transport. Our study suggests
that HONO could significantly increase the atmospheric oxidation capacity in a
street canyon which may impact the secondary formation of aerosols and OVOCs. |
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