Globally, ambient air pollution is linked to 4.2 million deaths every year. Recent research published in Science has shown that lightning may play an important role in removing harmful pollutants from the atmosphere. While lightning is normally considered a dangerous and potentially fatal component of thunderstorms, it plays a significant role in atmospheric chemistry. Previous research has confirmed that lightning produces the chemical compound nitric oxide (NO), leading to the formation of the other compounds ozone (O3) and hydroxyl radicals (OH). Hydroxyl radicals, a type of oxidant, are the main driver of chemical reactions in the atmosphere. Oxidants in general reduce the concentrations of ambient air pollution by reacting with contaminants, making them more water soluble and more likely to dissipate from the atmosphere through precipitation. However, prior to the research led by William Brune, there has been limited documented evidence of the role lightning-based oxidants play in the ambient air concentrations.
Researcher William Brune and his associates, including an undergraduate student, at Pennsylvania State University analyzed data collected by a NASA jet in storm clouds over Colorado, Oklahoma, and Texas to determine oxidant concentrations from lightning. These NASA jets measured two oxidants: OH and hydroperoxyl radical (HO2) in May and June of 2012. Laboratory testing then confirmed that both OH and HO2 could be produced via electrical spark. The NASA jet observed concentrations of the oxidant upwards of a thousand parts per trillion (ppt) in some storm clouds. These concentrations are orders of magnitude higher than previous measurements, with an OH recorded maximum of a few ppt and an HO2 of 150 ppt. These new measurements are likely due to geographic differences in sampling.
Estimates from this study indicate that lightning may be responsible for 2% to 16% of the atmosphere’s OH oxidation, a much higher concentration than previously expected. Previously, scientists thought very few oxidants were produced from lightning; however, this study shows lightning may instead be a considerable part of atmospheric pollution control. While there is some uncertainty in the findings given the lack of geographical variability in measurement locations, observation data open up a new understanding of chemical atmospheric reactions. These findings may be increasingly important as anthropogenic climate change drives increased thunderstorm activity and associated increases in ambient air pollution from fossil fuel consumption.
Dr. William H. Brune is a distinguished professor in the Department of Meteorology and Atmospheric Science at Penn State University where he studies atmospheric photochemistry, and atmospheric aerosol particle formation.
Managing Correspondent: Samantha Tracy
Press Article: “Lightning may be an important source of air-cleaning chemicals”
Journal Article: “Extreme oxidant amounts produced by lightning in storm clouds”
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