Increased pollution leads to increasing particulate concentrations. Since some particles nucleate drop formation, clouds will contain, with increasing pollution, more drops per unit volume, and hence will tend to be optically thicker and more reflecting. An opposite effect is also present, in that increasing absorption also attends increasing pollution. Measurements suggest that the former (brightening) effect is the dominant one for global climate and that the climatic effect is quite comparable to that of increased carbon dioxide, and acts in the opposite direction.

Increased pollution leads to increasing particulate concentrations. Since some particles nucleate drop formation, clouds will contain, with increasing pollution, more drops per unit volume, and hence will tend to be optically thicker and more reflecting. An opposite effect is also present, in that increasing absorption also attends increasing pollution. Measurements suggest that the former (brightening) effect is the dominant one for global climate and that the climatic effect is quite comparable to that of increased carbon dioxide, and acts in the opposite direction.

Electric field records have been computer analyzed to determine the lightning statistics for air‐mass thunderstorms at the NASA Kennedy Space Center, Florida. The results for 79 summer storms which produced 10 or more discharges during the years 1976–1980 indicate that cloud and cloud‐to‐ground discharges occur at a mean rate of about 2.4 discharges per minute per storm. The maximum flashing rate over a 5‐min interval was 30.6 discharges per minute on July 14, 1980. Estimates of the monthly area density of all discharges during June, July, and August 1974 through 1980 range from 4 to 27 discharges per km2 per month, with a systematic uncertainty of perhaps a factor of 2 in the sampled area. The mean and standard deviation of the monthly area density over the above years was 12±8 discharges per km2 per month, and the mean area density of just cloud‐to‐ground (CG) flashes is estimated to be 4.6±3.1 CG flashes per km2 per month. Tipping‐bucket rain gauges were operated at each field‐mill site during 1976, 1977, and 1978 as part of the Thunderstorm Research International Program, and the statistics on rainfall are given for 28 storms in 1977 and 1978. Two thunderstorms, one small and one large, were favorably located and relatively stationary, so that the lightning data and surface rainfall could be directly compared. In these storms, there was a good correlation between lightning and rainfall when the latter lagged the former by times of 4 and 9 min. The average rainfall associated with each lightning is estimated to be about 6.7×103 m3 per discharge during the small storm and about 8.5×103 m3 per discharge during the large storm. The average rain volumes associated with each cloud‐to‐ground flash are estimated to be 1.8×104 m3 per CG flash and 2.2×104 m3 per CG flash during these storms, values that are in good agreement with estimates by other investigators.

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