Arctic lightning and anthropogenic NOx emissions estimated from TROPOMI observations

<p>The Arctic is experiencing rapid climate change. The increasing temperature not only reduces the sea-ice extent but will also have doubled the number of lightning flashes by the end of the century. The unlocked Arctic ocean can also lead to increased human activities such as shipping and expanded oil and gas production. In addition, the increase of lightning will cause more wildfires. All of these above will give rise to emissions of nitrogen oxides (NO<sub>x</sub>).</p><p>In this study, we track and estimate three-year (2019-2021) Arctic NO<sub>x</sub> emissions by combing the TROPOspheric Monitoring Instrument (TROPOMI) observations, Visible Infrared Imaging Radiometer Suite (VIIRS) data, and the Vaisala’s Global Lightning Dataset (GLD360). The NO<sub>x</sub> emissions are divided into two different categories and estimated separately: 1) NO<sub>x</sub> emissions from lighting; 2) surface NO<sub>x</sub> emissions from all other sources.</p><p>The continuous overlapping orbits of TROPOMI passing over the Arctic provide unique opportunities for tracking the lightning NOx (LNO<sub>x</sub>) and calculating both LNO<sub>x</sub> lifetime and production efficiency. Previous studies focused on the LNO<sub>x</sub> emissions in the tropical and mid-latitude regions and estimated the global LNO<sub>x</sub> within the range of 2 to 8 T N yr-1. This study can add the missing LNO<sub>x</sub> productions in high latitudes.</p><p>Besides, a Cloud-Snow Differentiation (CSD) method is applied to get more high-precision TROPOMI observations over large boreal snow-covered areas by discriminating snow-covered surfaces from clouds. The derived NO<sub>x</sub> emissions from power plants, natural gas industries, and soil will play an important role in updating the present-day NO<sub>x</sub> inventories which have a limited number of data sets. This study highlights the potential of TROPOMI as well as future satellite missions for monitoring Arctic NO<sub>x</sub> emissions.</p>