Retrievals of tropospheric NO columns from UV–visible observationsof reflected sunlight require a priori vertical profiles to account for thevariation in sensitivity of the observations to NO at differentaltitudes. These profiles vary in space and time but are usually approximatedusing models that do not resolve the full details of this variation.Currently, no operational retrieval simulates these a priori profiles at bothhigh spatial and high temporal resolution. Here we examine the additionalbenefits of daily variations in a priori profiles for retrievals alreadysimulating a priori NO profiles at sufficiently high spatialresolution to identify variations of NO within urban plumes. We showthe effects of introducing daily variation into a priori profiles can be aslarge as 40 % and 3 × 10 molec. cm for an individualday and lead to corrections as large as −13 % for a monthly average ina case study of Atlanta, GA, USA. Additionally, we show that NO emissionsestimated from space-based remote sensing using daily, high-spatial-resolutiona priori profiles are ∼ 100 % greater than those of aretrieval using spatially coarse a priori profiles, and 26–40 % lessthan those of a retrieval using monthly averaged high-spatial-resolutionprofiles.
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