The Role of Lightning in Atmospheric Chemistry

Abstract

Lightning has important effects on atmospheric constituents in primarily the middle and upper troposphere. We summarize the effects of lightning on atmospheric chemistry that have been published since the last major review in 2007. The estimates of NO _x production by lightning (LNO _x ) are based on five methods: theoretical/laboratory estimates applied to flash observations; aircraft measurements in storm anvils; cloud resolved modeling constrained by observations; satellite retrievals of NO ₂ columns; and global and regional models constrained by aircraft or satellite data. The resulting best estimate of global LNO _x production is 5 ± 2 Tg N yr ⁻¹ , which represents a small narrowing of the range from previous estimates. Model (observational) estimates are on average at the upper (lower) ends of this range. LNO _x production efficiency (PE) corresponding to this range is 150–350 mol fl ⁻¹ . An inverse relationship between flash rate and LNO _x PE has been ascertained from satellite and aircraft measurements. Direct O ₃ and HO _x production in corona discharges and HO _x from subvisible flashes may be sufficiently large to warrant inclusion in models. LNO _x leads to photochemical O ₃ production in the upper troposphere at rates of 5–10 ppbv d ⁻¹ and contributes 1–2 ppbv to maximum 8‐hr surface O ₃ (greater amounts not uncommon over higher terrain). CH ₄ lifetime decreases by ∼5% per Tg N yr ⁻¹ increase of LNO _x . Globally, no significant long‐term trends in lightning flash rate have been observed, but regional trends have been detected. Future flash rate trends and LNO _x emissions remain uncertain.