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. there was still a great deal of smog, now identified as photochemical smog, despite the changes. the major remaining problem was

The major remaining problem was the large distances driven daily by solitary commuters

Explanation:

Photochemical smog occurs when nitrogen oxides and volatile organic compounds mix together in the presence of sunlight which acts as a catalyst and form ozone at lower levels.

Even though measures such as ban of incinerators and regulation of evaporation of gasoline were instated  photochemical smog was still present because people drive for a long time to get to work.

As far as photochemical smog is concerned it the combustion of other fossil fuels, such as gasoline by motor vehicles and industry is seen as its main contributor. Combustion releases primary pollutants: volatile organic compounds and nitrogen oxides. These pollutants are the main cause of photochemical combustion.

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question - in 1827, john walker, a druggist in a small english town, tipped a splint with sulphur, chlorate of potash, and sulphid of antimony, and rubbed it on sandpaper, and it burst into flame. the druggist had discovered the first friction-chemical match, the kind we use to-day. it is called friction-chemical because it is made by mixing certain chemicals together and rubbing them. although walker's match did not require the bottle of acid, nevertheless it was not a good one. it could be lighted only by hard rubbing, and it sputtered and threw fire in all directions. in a few years, however, phosphorus was substituted on the tip for antimony, and the change worked wonders. the match could now be lighted with very little rubbing, and it was no longer necessary to have sandpaper upon which to rub it. it would ignite when rubbed on any dry surface, and there was no longer any sputtering. this was the phosphorus match, the match with which we are so familiar. according the paragraph what was the benefit of the new phosphorus match? it burst into flame when rubbed on sandpaper. it was made by mixing chemicals. it could be ignited on any dry surface. it threw fire in all directions.

answer - matches required natural chemicals