In 1958 trash collection programs were established, and backyard incinerators were banned in the hope of reducing smog. however, it was estimated that massive amounts of gasoline were evaporating from storage tanks, fuel pump nozzles, and delivery trucks. this was also considered a serious contributor to smog, and over the next 20 years several new rules, and several new devices, were put in place to alleviate it. despite the changes, there was still a great deal of photochemical smog. the major remaining problem was