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| Titel |
Four years of ground-based MAX-DOAS observations of HONO and NO2 in the Beijing area |
| VerfasserIn |
F. Hendrick, J.-F. Müller, K. Clémer, P. Wang, M. Mazière, C. Fayt, C. Gielen, C. Hermans, J. Z. Ma, G. Pinardi, T. Stavrakou, T. Vlemmix, M. Roozendael |
| 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 ; 14, no. 2 ; Nr. 14, no. 2 (2014-01-22), S.765-781 |
| Datensatznummer |
250118304
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| Publikation (Nr.) |
 copernicus.org/acp-14-765-2014.pdf |
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| Zusammenfassung |
| Ground-based Multi-Axis Differential Optical Absorption Spectroscopy
(MAX-DOAS) measurements of nitrous acid (HONO) and its precursor NO2
(nitrogen dioxide) as well as aerosols have been performed daily in Beijing
city centre (39.98° N, 116.38° E) from July 2008 to
April 2009 and at the suburban site of Xianghe (39.75° N,
116.96° E) located ~60 km east of Beijing from March
2010 to December 2012. This extensive dataset allowed for the first time
the investigation of the seasonal cycle of HONO as well as its diurnal
variation in and in the vicinity of a megacity. Our study was focused on the
HONO and NO2 near-surface concentrations (0–200 m layer) and total
vertical column densities (VCDs) and also aerosol optical depths (AODs) and
extinction coefficients retrieved by applying the Optimal Estimation Method
to the MAX-DOAS observations. Monthly averaged HONO near-surface
concentrations at local noon display a strong seasonal cycle with a maximum
in late fall/winter (~0.8 and 0.7 ppb at Beijing and Xianghe,
respectively) and a minimum in summer (~0.1 ppb at Beijing
and 0.03 ppb at Xianghe). The seasonal cycles of HONO and NO2 appear to
be highly correlated, with correlation coefficients in the 0.7–0.9 and
0.5–0.8 ranges at Beijing and Xianghe, respectively. The stronger
correlation of HONO with NO2 and also with aerosols observed in Beijing
suggests possibly larger role of NO2 conversion into HONO in the
Beijing city center than at Xianghe. The observed diurnal cycle of HONO
near-surface concentration shows a maximum in the early morning (about 1 ppb
at both sites) likely resulting from night-time accumulation, followed by a
decrease to values of about 0.1–0.4 ppb around local noon. The HONO / NO2
ratio shows a similar pattern with a maximum in the early morning (values up
to 0.08) and a decrease to ~0.01–0.02 around local noon. The
seasonal and diurnal cycles of the HONO near-surface concentration are found
to be similar in shape and in relative amplitude to the corresponding cycles
of the HONO total VCD and are therefore likely driven mainly by the balance
between HONO sources and the photolytic sink, whereas dilution effects
appear to play only a minor role. The estimation of OH radical production
from HONO and O3 photolysis based on retrieved HONO near-surface
concentrations and calculated photolysis rates indicate that in the 0–200 m
altitude range, HONO is by far the largest source of OH radicals in winter
as well as in the early morning at all seasons, while the contribution of
O3 dominates in summer from mid-morning until mid-afternoon. |
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