For three California cities of various sizes, two-meter-level temperature patterns were determined by intensive traverses with automobile-mounted thermistors, and vertical temperature gradients in the lowest 1000 feet were measured by wiresonde simultaneously at urban centers and peripheral open areas. In 35 evening surveys under varying weather conditions, a characteristic horizontal temperature pattern existed for each city. Temperatures increased from peripheral open lands to built-up center in direct proportion to structure density. Characteristics of the urban gradients have been analyzed in relation to city size and to meteorological parameters. Vertical temperature data showed that built-up areas frequently caused instability up to about 3 times roof height in otherwise stable air and that a “crossover” point sometimes existed above which the air over the urban center was cooler than that over surrounding country.

Insights from dendrochronology have provided a new seasonal predictor for air pollution meteorology. In the San Francisco Bay Area summer ozone excesses over the federal ozone standard are correlated (correlation coefficient r = .87) with precipitation for the two preceding winters, a factor related to tree-ring width in a precipitation-stressed climate. The hypothesis that reactive hydrocarbon emissions from vegetative biomass affects these ozone excesses was supported by a similar correlation between summer hydrocarbon average maximums and the two-winter precipitation factor, reaching r = .88 at suburban stations. A weak tendency for hot summers to follow wet winters (in 16 years of California data) explains only a minor part of the ozone-rain relationship in multiple correlations.

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