Extreme oxidant amounts produced by lightning in storm clouds

Area of Science:

• Atmospheric Chemistry and Physics
• Thunderstorm Electrification and Dynamics

Background:

• Lightning's role in atmospheric chemistry is primarily linked to nitric oxide (NO) production, influencing ozone (O3) and hydroxyl radical (OH) formation.
• The direct contribution of lightning to the production of key oxidants like OH and hydroperoxyl radical (HO2) has been poorly quantified.

Purpose of the Study:

• To investigate the direct production of hydroxyl (OH) and hydroperoxyl (HO2) radicals by lightning.
• To quantify the magnitude of lightning-generated OH and HO2 during deep convection events.

Main Methods:

• Analysis of airborne measurements from a 2012 deep convection and chemistry study.
• Correlation of oxidant concentrations (OH, HO2) with observed lightning activity, including visible flashes and subvisible discharges.

Main Results:

• Direct generation of exceptionally high concentrations of OH and HO2 radicals by lightning was observed.
• Elevated OH and HO2 levels were directly linked to both visible lightning flashes and subvisible electrical discharges in anvil regions.
• Observed OH and HO2 enhancements were orders of magnitude greater than previously recorded atmospheric concentrations.

Conclusions:

• Lightning is a significant direct source of atmospheric oxidants OH and HO2.
• Globally, lightning-generated OH may account for a substantial 2-16% of total atmospheric OH oxidation, impacting the atmosphere's self-cleaning capacity.
• This finding necessitates a re-evaluation of the role of lightning in global atmospheric chemistry and oxidant budgets.