Ozone and point discharge measurements under thunderclouds

Abstract

Short duration increases in the concentration of atmospheric ozone have been observed beneath active New Mexican thunderstorms in the vicinity of an exposed and grounded sharp metal rod. These ozone transients immediately follow the emission of charge into the air from the metal point under the influence of atmospheric electricity. The increases are greater when they are associated with negative charge emission than when they are associated with positive; the maximum ozone concentration above lightning-induced emission of negative charge has been about 6.4 times that of the fine weather concentration (about six ozone molecules per hundred million air molecules). Longer duration increases in the atmospheric ozone to about 1.5 times the prestorm concentration are found above a collection of natural grass points when overhead clouds are electrified with a net positive charge. Our comparison of the ultraviolet radiation pulses from negative and positive point to plane discharges suggests to us a photochemical explanation for the relatively large production of ozone by negative charge emission. Whereas much of the ozone found aloft appears to have been transported by updrafts from the surface, the concentrations observed in an electrified cloud were greater than those near the earth. We find that ozone is produced by the point discharge from the surfaces of water droplets under intense electric fields; this process may account for some of the ozone observed in thunderclouds.