New observations of NO 2 in the upper troposphere from TROPOMI

Marais, Eloise A.; Roberts, John F.; Ryan, Robert G.; Eskes, Henk; Boersma, K. Folkert; Choi, Sungyeon; Joiner, Joanna; Abuhassan, Nader; Redondas, Alberto; Grutter, Michel; Cede, Alexander; Gomez, Laura; Navarro-Comas, Monica

Nitrogen oxides (inline-formula M3inlinescrollmathml chem normal NO x chem normal NO + chem normal NO normal 2 85pt13ptsvg-formulamathimg72fae000e07cdf06702a94248543dc74 amt-14-2389-2021-ie00001.svg85pt13ptamt-14-2389-2021-ie00001.png ) in the inline-formulaNOx-limited upper troposphere (UT) are long-lived and so have a large influence on the oxidizing capacity of the troposphere and formation of the greenhouse gas ozone. Models misrepresent inline-formulaNOx in the UT, and observations to address deficiencies in models are sparse. Here we obtain a year of near-global seasonal mean mixing ratios of inline-formulaNO2 in the UT (450–180 hPa) at inline-formula M7inlinescrollmathml normal 1 × normal 1 34pt11ptsvg-formulamathimg2f0cd8b2e0fda9823788cc41d80ac5a2 amt-14-2389-2021-ie00002.svg34pt11ptamt-14-2389-2021-ie00002.png by applying cloud-slicing to partial columns of inline-formulaNO2 from TROPOMI. This follows refinement of the cloud-slicing algorithm with synthetic partial columns from the GEOS-Chem chemical transport model. TROPOMI, prior to cloud-slicing, is corrected for a 13 % underestimate in stratospheric inline-formulaNO2 variance and a 50 % overestimate in free-tropospheric inline-formulaNO2 determined by comparison to Pandora total columns at high-altitude free-tropospheric sites at Mauna Loa, Izaña, and Altzomoni and MAX-DOAS and Pandora tropospheric columns at Izaña. Two cloud-sliced seasonal mean UT inline-formulaNO2 products for June 2019 to May 2020 are retrieved from corrected TROPOMI total columns using distinct TROPOMI cloud products that assume clouds are reflective boundaries (FRESCO-S) or water droplet layers (ROCINN-CAL). TROPOMI UT inline-formulaNO2 typically ranges from 20–30 pptv over remote oceans to inline-formula>80 pptv over locations with intense seasonal lightning. Spatial coverage is mostly in the tropics and subtropics with FRESCO-S and extends to the midlatitudes and polar regions with ROCINN-CAL, due to its greater abundance of optically thick clouds and wider cloud-top altitude range. TROPOMI UT inline-formulaNO2 seasonal means are spatially consistent (inline-formulaR=0.6–0.8) with an existing coarser spatial resolution (5inline-formula latitude inline-formula× 8inline-formula longitude) UT inline-formulaNO2 product from the Ozone Monitoring Instrument (OMI). UT inline-formulaNO2 from TROPOMI is 12–26 pptv more than that from OMI due to increase in inline-formulaNO2 with altitude from the OMI pressure ceiling (280 hPa) to that for TROPOMIpage2390 (180 hPa), but possibly also due to altitude differences in TROPOMI and OMI cloud products and inline-formulaNO2 retrieval algorithms. The TROPOMI UT inline-formulaNO2 product offers potential to evaluate and improve representation of UT inline-formulaNOx in models and supplement aircraft observations that are sporadic and susceptible to large biases in the UT.

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Marais, Eloise A. / Roberts, John F. / Ryan, Robert G. / et al: New observations of NO2 in the upper troposphere from TROPOMI. 2021. Copernicus Publications.

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