Spaceborne Observations of Lightning NO 2 in the Arctic.

The Arctic region is experiencing notable warming as well as more lightning. Lightning is the dominant source of upper tropospheric nitrogen oxides (NO x ), which are precursors for ozone and hydroxyl radicals. In this study, we combine the nitrogen dioxide (NO 2 ) observations from the TROPOspheric Monitoring Instrument (TROPOMI) with Vaisala Global Lightning Dataset 360 to evaluate lightning NO 2 (LNO 2 ) production in the Arctic. By analyzing consecutive TROPOMI NO 2 observations, we determine the lifetime and production efficiency of LNO 2 during the summers of 2019-2021. Our results show that the LNO 2 production efficiency over the ocean is ∼6 times higher than over continental regions. Additionally, we find that a higher LNO 2 production efficiency is often correlated with lower lightning rates. The summertime lightning NO x emission in the Arctic (north of 70° N) is estimated to be 219 ± 116 Mg of N, which is equal to 5% of anthropogenic NO x emissions. However, for the span of a few hours, the Arctic LNO 2 density can even be comparable to anthropogenic NO 2 emissions in the region. These new findings suggest that LNO 2 can play an important role in the upper-troposphere/lower-stratosphere atmospheric chemical processes in the Arctic, particularly during the summer.