In areas where large quantities of fossil fuels are used, sulfur oxides can be a major air pollution problem. These contaminants can damage vegetation and affect the health of both humans and animals. In the past, sulfur oxides were a problem in the Bay Area, especially in the vicinity of the large oil refineries and chemical plants in Contra Costa County. The Bay Area Air Quality Management District has been controlling emissions from these sources since 1961, however, and no state or federal excesses have been recorded at District monitoring stations since 1976. This is an odorless, invisible gas which affects the health of people exposed to high concentrations.
Carbon monoxide is especially dangerous indoors, when ventilation is inadequate.
Almost 70 percent of the Bay Area's carbon monoxide comes from motor vehicles. A substantial amount also comes from burning wood in fireplaces and woodstoves. State and federal controls on new cars and voluntary efforts to reduce woodburning have been implemented to prevent carbon monoxide from reaching adverse levels. It discolors paints and tarnishes many metals. This gas is produced largely at sewage treatment plants and at oil refineries as a by-product in refining crude oil.