Spaceborne Observations of Lightning NO 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), which are precursors for ozone and hydroxyl radicals. In this study, we combine the nitrogen dioxide (NO) observations from the TROPOspheric Monitoring Instrument (TROPOMI) with Vaisala Global Lightning Dataset 360 to evaluate lightning NO (LNO) production in the Arctic. By analyzing consecutive TROPOMI NO observations, we determine the lifetime and production efficiency of LNO during the summers of 2019-2021. Our results show that the LNO production efficiency over the ocean is ∼6 times higher than over continental regions. Additionally, we find that a higher LNO production efficiency is often correlated with lower lightning rates. The summertime lightning NO 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 emissions. However, for the span of a few hours, the Arctic LNO density can even be comparable to anthropogenic NO emissions in the region. These new findings suggest that LNO can play an important role in the upper-troposphere/lower-stratosphere atmospheric chemical processes in the Arctic, particularly during the summer.