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INTERCOMPARISON OF SCIAMACHY AND OMI TROPOSPHERIC NO2 COLUMNS: OBSERVING THE DIURNAL EVOLUTION OF CHEMISTRY AND EMISSIONS FROM SPACE
Citation:
BOERSMA, K., D. J. JACOB, H. J. ESKES, R. W. PINDER, J. WANG, AND R. J. VAN DER A. INTERCOMPARISON OF SCIAMACHY AND OMI TROPOSPHERIC NO2 COLUMNS: OBSERVING THE DIURNAL EVOLUTION OF CHEMISTRY AND EMISSIONS FROM SPACE. JOURNAL OF GEOPHYSICAL RESEARCH. American Geophysical Union, Washington, DC, 113(D16S26):1-14, (2008).
Impact/Purpose:
The objective of this task is to thoroughly characterize the performance of the emissions, meteorological and chemical/transport modeling components of the Models-3 system, with an emphasis on the chemical/transport model, CMAQ. Emissions-based models are composed of highly complex scientific hypotheses concerning natural processes that can be evaluated through comparison with observations, but not truly validated. Static and Dynamic Operational, Diagnostic, and ultimately Probablistic evaluation methods are needed to both establish credibility and build confidence within the client and scientific community in the simulations results for policy and scientific applications. The characterization of the performance of Models-3/CMAQ is also a tool for the model developers to identify aspects of the modeling system that require further improvement.
Description:
Concurrent (August 2006) satellite measurements of tropospheric NO2 columns from OMI aboard Aura (13:30 local overpass time) and SCIAMACHY aboard Envisat (10:00 overpass) offer an opportunity to examine the consistency between the two instruments under tropospheric background conditions and the effect of different observing times. For scenes with tropospheric NO2 columns <5.0×1015 molec.cm-2, SCIAMACHY and OMI agree within 1.0–2.0×1015 molec.cm-2, consistent with the detection limits of both instruments. We find evidence for a low bias of 0.2×10 15 molec.cm-2 in OMI observations over remote oceans. Over the fossil fuel source regions at northern mid-latitudes, we find that SCIAMACHY observes up to 40% higher NO2 at 10:00 local time than OMI at 13:30. Over biomass burning regions in the tropics, SCIAMACHY observes up to 40% lower NO2 columns than OMI. These differences are present in the spectral fitting of the data (slant column), and are augmented in the fossil fuel regions, and dampened in the tropical biomass burning regions by the expected increase in air mass factor as the mixing depth rises from 10:00 to 13:30. Using a global 3-D chemical transport model (GEOSChem), we show that the 10:00–13:30 decrease in tropospheric NO2 column over fossil fuel source regions can be explained by photochemical loss, dampened by the diurnal cycle of anthropogenic emissions that has a broad daytime maximum. The observed 10:00–13:30 NO2 column increase over tropical biomass burning regions points to a sharp midday peak in emissions, and is consistent with a diurnal cycle of emissions derived from geostationary satellite fire counts.