Influence of Lightning NOx on Near-Surface Air Quality

Lightning is an important source of NO_x in the free troposphere, which not only affects the tropospheric chemistry but also has broad impacts on nitrogen deposition and biospheres. Moreover, lightning NO_x vertical distributions play a key role in the retrieval of NO₂ vertical column densities. However, the NO_x production rate of lightning, the vertical characteristics of lightning NO_x, and the influence of lightning NO_x on air quality are still full of controversies and uncertainties. This study applies a cloud slicing method to derive lightning NO_x vertical distributions in the free troposphere through mapping the Ozone Monitoring Instrument measurements on the National Lightning Detection Network observations. Two types of lightning NO_x distributions, as well as their spatial distributions over the United States, are identified. A cloud-resolving chemical and transport model well reproduce these observed features and the effect of lightning on near-surface air quality is evaluated with EPA observations. It is suggested that current mesoscale air quality models underestimate the downdraft effect of some storms in the Deep South and the Southwest.