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Abstract. Nitrogen oxides (NOx≡NO+NO2) inthe NOx-limited upper troposphere (UT) are long-lived and so have alarge influence on the oxidizing capacity of the troposphere and formationof the greenhouse gas ozone. Models misrepresent NOx 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 NO2 in the UT (450–180 hPa) at 1∘×1∘ by applyingcloud-slicing to partial columns of NO2 from TROPOMI. This followsrefinement of the cloud-slicing algorithm with synthetic partial columnsfrom the GEOS-Chem chemical transport model. TROPOMI, prior tocloud-slicing, is corrected for a 13 % underestimate in stratosphericNO2 variance and a 50 % overestimate in free-tropospheric NO2 determined by comparison to Pandora total columns at high-altitude free-tropospheric sites at Mauna Loa, Izaña, and Altzomoni and MAX-DOAS andPandora tropospheric columns at Izaña. Two cloud-sliced seasonal mean UTNO2 products for June 2019 to May 2020 are retrieved from correctedTROPOMI total columns using distinct TROPOMI cloud products that assumeclouds are reflective boundaries (FRESCO-S) or water droplet layers(ROCINN-CAL). TROPOMI UT NO2 typically ranges from 20–30 pptv over remote oceans to &gt;80 pptv over locations with intense seasonal lightning. Spatial coverage is mostly in the tropics and subtropics withFRESCO-S and extends to the midlatitudes and polar regions with ROCINN-CAL,due to its greater abundance of optically thick clouds and wider cloud-topaltitude range. TROPOMI UT NO2 seasonal means are spatially consistent (R=0.6–0.8) with an existing coarser spatial resolution (5∘latitude × 8∘ longitude) UT NO2 product from theOzone Monitoring Instrument (OMI). UT NO2 from TROPOMI is 12–26 pptvmore than that from OMI due to increase in NO2 with altitude from the OMI pressure ceiling (280 hPa) to that for TROPOMI (180 hPa), but possiblyalso due to altitude differences in TROPOMI and OMI cloud products andNO2 retrieval algorithms. The TROPOMI UT NO2 product offerspotential to evaluate and improve representation of UT NOx in models and supplement aircraft observations that are sporadic and susceptible to large biases in the UT.

New observations of NO&lt;sub&gt;2&lt;/sub&gt; in the upper troposphere from TROPOMI

New observations of NO<sub>2</sub> in the upper troposphere from TROPOMI