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

By Jintai Lin, Randall V. Martin, K. Boersma, Maarten Sneep, Piet Stammes, Robert J. D. Spurr, Pucai C. Wang, Michel Van Roozendael, K. Clémer, Hitoshi Irie. 2013

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Retrievals of tropospheric nitrogen dioxide (NO2) from the Ozone Monitoring Instrument (OMI) are subject to errors in the treatments of aerosols, surface reflectance anisotropy, and vertical profile of NO 2. Here we quantify the influences over China via an improved retrieval pro- cess. We explicitly account for aerosol optical effects (simu- lated by nested GEOS-Chem at 0.667 long. ◊ 0.5 lat. and constrained by aerosol measurements), surface reflectance anisotropy, and high-resolution vertical profiles of NO 2 (sim- ulated by GEOS-Chem). Prior to the NO2 retrieval, we derive the cloud information using consistent ancillary assumptions. We compare our retrieval to the widely used DOMINO v2 product, using MAX-DOAS measurements at three ur- ban/suburban sites in East China as reference and focusing the analysis on the 127 OMI pixels (in 30 days) closest to the MAX-DOAS sites. We find that our retrieval reduces the interference of aerosols on the retrieved cloud properties, thus enhancing the number of valid OMI pixels by about 25 %. Compared to DOMINO v2, our retrieval better cap- tures the day-to-day variability in MAX-DOAS NO2 data (R 2 = 0.96 versus 0.72), due to pixel-specific radiative trans- fer calculations rather than the use of a look-up table, ex- plicit inclusion of aerosols, and consideration of surface re- flectance anisotropy. Our retrieved NO 2 columns are 54 % of the MAX-DOAS data on average, reflecting the inevitable spatial inconsistency between the two types of measurement, errors in MAX-DOAS data, and uncertainties in our OMI re- trieval related to aerosols and vertical profile of NO 2. Sensitivity tests show that excluding aerosol optical effects can either increase or decrease the retrieved NO2 for individ- ual OMI pixels with an average increase by 14 %. Excluding aerosols also complexly affects the retrievals of cloud frac- tion and particularly cloud pressure. Employing various sur- face albedo data sets slightly affects the retrieved NO 2 on average (within 10 %). The retrieved NO2 columns increase when the NO2 profiles are taken from MAX-DOAS retrievals (by 19 % on average) or TM4 simulations (by 13 %) in- stead of GEOS-Chem simulations. Our findings are also rel- evant to retrievals of other pollutants (e.g., sulfur dioxide,

Subfields: Atmospheric Science, Global and Planetary Change

View Paper: https://www.semanticscholar.org/paper/03a272085723418b2bb17f570efc3eb009d60514