There's bad news mixed with the good, however. Ozone concentrations located miles above the surface clean pollutants from the air, contribute to global warming, and protect us from dangerous ultraviolet radiation. Three years ago, Jacob and research associate Jennifer Logan assigned freshmen the task of determining how air pollution changed in the students' hometowns from 1980 to 1995. The students checked the Los Angeles area and found a surprising drop in ozone, especially during summer afternoons. The oxides result from burning gasoline, natural gas, coal, diesel fuel, and other so-called fossil fuels.
Hydrocarbons are easily vaporized compounds containing hydrogen and carbon.
Small dust and soot particles added to the mix give it the foggy, sometimes brownish look, which people call smog. Hydrocarbons also come from the tailpipes of vehicles and from gasoline pumps, which has led to laws requiring catalytic converters and seals on gas-pump nozzles. In Los Angeles, New York, and Chicago, human-generated hydrocarbons are high, but emissions from trees are low. This has not been the case in the rest of the country. Take Boston, for example.