Retrieving tropospheric nitrogen dioxide from the Ozone Monitoring Instrument: effects of aerosols, surface reflectance anisotropy, and vertical profile of nitrogen dioxide

摘要

Retrievals of tropospheric nitrogen dioxide (NO) from the OzoneMonitoring Instrument (OMI) are subject to errors in the treatments ofaerosols, surface reflectance anisotropy, and vertical profile of NO.Here we quantify the influences over China via an improved retrievalprocess. We explicitly account for aerosol optical effects (simulated bynested GEOS-Chem at 0.667° long. × 0.5° lat.and constrained by aerosol measurements), surface reflectance anisotropy,and high-resolution vertical profiles of NO (simulated by GEOS-Chem).Prior to the NO retrieval, we derive the cloud information usingconsistent ancillary assumptions.We compare our retrieval to the widely used DOMINO v2 product, using MAX-DOAS measurements at three urban/suburban sites in East China asreference and focusing the analysis on the 127 OMI pixels (in 30 days) closest to theMAX-DOAS sites. We find that our retrieval reduces the interference ofaerosols on the retrieved cloud properties, thus enhancing the number ofvalid OMI pixels by about 25%. Compared to DOMINO v2, our retrievalbetter captures the day-to-day variability in MAX-DOAS NO data( = 0.96 versus 0.72), due to pixel-specific radiative transfercalculations rather than the use of a look-up table, explicit inclusion ofaerosols, and consideration of surface reflectance anisotropy. Our retrievedNO columns are 54% of the MAX-DOAS data on average, reflecting theinevitable spatial inconsistency between the two types of measurement,errors in MAX-DOAS data, and uncertainties in our OMI retrieval related toaerosols and vertical profile of NO.Sensitivity tests show that excluding aerosol optical effects can eitherincrease or decrease the retrieved NO for individual OMI pixels withan average increase by 14%. Excluding aerosols also complexly affects theretrievals of cloud fraction and particularly cloud pressure. Employingvarious surface albedo data sets slightly affects the retrieved NO onaverage (within 10%). The retrieved NO columns increase when theNO profiles are taken from MAX-DOAS retrievals (by 19% on average)or TM4 simulations (by 13%) instead of GEOS-Chem simulations. Ourfindings are also relevant to retrievals of other pollutants (e.g., sulfurdioxide, ormaldehyde, glyoxal) from UV–visible backscatter satelliteinstruments.