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| Titel |
Influence of aerosols and surface reflectance on satellite NO2 retrieval: seasonal and spatial characteristics and implications for NOx emission constraints |
| VerfasserIn |
J.-T. Lin, M.-Y. Liu, J.-Y. Xin, K. F. Boersma, R. Spurr, R. Martin, Q. Zhang |
| 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. 19 ; Nr. 15, no. 19 (2015-10-09), S.11217-11241 |
| Datensatznummer |
250120086
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| Publikation (Nr.) |
 copernicus.org/acp-15-11217-2015.pdf |
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| Zusammenfassung |
Satellite retrievals of vertical column densities (VCDs) of tropospheric
nitrogen dioxide (NO2) normally do not explicitly account for aerosol
optical effects and surface reflectance anisotropy that vary with space and
time. Here, we conduct an improved retrieval of NO2 VCDs over China,
called the POMINO algorithm, based on measurements from the Ozone Monitoring
Instrument (OMI), and we test the importance of a number of aerosol and
surface reflectance treatments in this algorithm. POMINO uses a parallelized
LIDORT-driven AMFv6 package to derive tropospheric air mass factors via
pixel-specific radiative transfer calculations with no look-up tables, taking
slant column densities from DOMINO v2. Prerequisite cloud optical properties
are derived from a dedicated cloud retrieval process that is fully consistent
with the main NO2 retrieval. Aerosol optical properties are taken from
GEOS-Chem simulations constrained by MODIS aerosol optical depth (AOD)
data. MODIS bi-directional reflectance distribution function (BRDF) data
are used for surface reflectance over land. For the present analysis, POMINO
level-2 data for 2012 are aggregated into monthly means on a 0.25°
long. × 0.25° lat. grid.
POMINO-retrieved annual mean NO2 VCDs vary from
15–25 × 1015 cm−2 over the polluted North China Plain
(NCP) to below 1015 cm−2 over much of western China. Using POMINO
to infer Chinese emissions of nitrogen oxides leads to annual anthropogenic
emissions of 9.05 TgN yr−1, an increase from 2006 (Lin, 2012) by about
19 %. Replacing the MODIS BRDF data with the OMLER v1 monthly
climatological albedo data affects NO2 VCDs by up to 40 % for
certain locations and seasons. The effect on constrained NOx emissions
is small. Excluding aerosol information from the retrieval process (this is
the traditional "implicit" treatment) enhances annual mean NO2 VCDs by
15–40 % over much of eastern China. Seasonally, NO2 VCDs are
reduced by 10–20 % over parts of the NCP in spring and over northern
China in winter, despite the general enhancements in summer and fall. The
effect on subsequently constrained annual emissions is between −5 and
+30 % with large seasonal and spatial dependence. The implicit aerosol
treatment also tends to exclude days with high pollution, since aerosols are
interpreted as effective clouds and the respective OMI pixels are often
excluded by cloud screening; this is a potentially important sampling bias.
Therefore an explicit treatment of aerosols is important for space-based
NO2 retrievals and emission constraints. A comprehensive independent
measurement network with sufficient spatial and temporal representativeness
is needed to further evaluate the different satellite retrieval approaches. |
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