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| Titel |
OMI tropospheric NO2 air mass factors over South America: effects of biomass burning aerosols |
| VerfasserIn |
P. Castellanos, K. F. Boersma, O. Torres, J. F. de Haan |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 8, no. 9 ; Nr. 8, no. 9 (2015-09-18), S.3831-3849 |
| Datensatznummer |
250116581
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| Publikation (Nr.) |
 copernicus.org/amt-8-3831-2015.pdf |
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| Zusammenfassung |
| Biomass burning is an important and uncertain source of aerosols and
NOx (NO + NO2) to the atmosphere. Satellite observations of
tropospheric NO2 are essential for characterizing this emissions
source, but inaccuracies in the retrieval of NO2 tropospheric columns
due to the radiative effects of aerosols, especially light-absorbing
carbonaceous aerosols, are not well understood. It has been shown that the
O2–O2 effective cloud fraction and pressure retrieval is sensitive
to aerosol optical and physical properties, including aerosol optical depth
(AOD). Aerosols implicitly influence the tropospheric air mass factor (AMF)
calculations used in the NO2 retrieval through the effective cloud
parameters used in the independent pixel approximation. In this work, we
explicitly account for the effects of biomass burning aerosols in the Ozone
Monitoring Instrument (OMI) tropospheric NO2 AMF calculation for
cloud-free scenes. We do so by including collocated aerosol extinction
vertical profile observations from the CALIOP instrument, and aerosol
optical depth (AOD) and single scattering albedo (SSA) retrieved by the OMI
near-UV aerosol algorithm (OMAERUV) in the DISAMAR radiative transfer model.
Tropospheric AMFs calculated with DISAMAR were benchmarked against AMFs
reported in the Dutch OMI NO2 (DOMINO) retrieval; the mean and standard
deviation of the difference was 0.6 ± 8 %. Averaged over three
successive South American biomass burning seasons (2006–2008), the spatial
correlation in the 500 nm AOD retrieved by OMI and the 532 nm AOD retrieved
by CALIOP was 0.6, and 68 % of the daily OMAERUV AOD observations were
within 30 % of the CALIOP observations. Overall, tropospheric AMFs
calculated with observed aerosol parameters were on average 10 % higher
than AMFs calculated with effective cloud parameters. For effective cloud
radiance fractions less than 30 %, or effective cloud pressures greater
than 800 hPa, the difference between tropospheric AMFs based on implicit and
explicit aerosol parameters is on average 6 and 3 %, respectively,
which was the case for the majority of the pixels considered in our study;
70 % had cloud radiance fraction below 30 %, and 50 % had effective
cloud pressure greater than 800 hPa. Pixels with effective cloud radiance
fraction greater than 30 % or effective cloud pressure less than 800 hPa
corresponded with stronger shielding in the implicit aerosol correction
approach because the assumption of an opaque effective cloud underestimates
the altitude-resolved AMF; tropospheric AMFs were on average 30–50 %
larger when aerosol parameters were included, and for individual pixels
tropospheric AMFs can differ by more than a factor of 2. The
observation-based approach to correcting tropospheric AMF calculations for
aerosol effects presented in this paper depicts a promising strategy for a
globally consistent aerosol correction scheme for clear-sky pixels. |
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