The concentration of seven toxic chemicals responsible for most of the known cancer risk from airborne contaminants in California dropped between 1990 and 2012, a study by the California Air Resources Board has found.
Published this month in the journal Environmental Science & Technology, the study found steep reductions in chemicals such as benzene and perchloroethylene, which is used in dry cleaning.
The declines were attributed to practices spurred by the board such as requiring filters on diesel trucks, or the purchase of new, less polluting diesel truck fleets. The board also offered grants encouraging dry cleaners to switch to more environmental friendly processes such as wet cleaning or the use of hydrocarbon cleaning machines.
“We knew that particulate matter was being reduced by the addition of filters on trucks, but that has only been occurring the least 10 years,” said Bart Croes, a board researcher and one of the study’s authors. “So we were pleasantly surprised at how large the reductions have been.”
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The presence of some chemicals such as benzene fell by about 90 percent despite a 31 percent growth in population and an 81 percent jump in diesel vehicle miles driven between 1990 and 2012, the study found. Benzene is used in motor fuels, solvents and pesticides and is a carcinogen linked to leukemia and a host of other illnesses.
The collective cancer risk from exposure to the seven chemicals fell by 76 percent over the 23-year period.
Results were gleaned from data from 17 air monitoring stations, including in the Bay Area and South Coast air basins.
Particulate matter from diesel exhaust, considered one of the more significant air pollutants, also declined by 68 percent despite population gains.
Recent studies of short-term increases in particle pollution have linked them to a rise in heart attacks and inflammation of lung tissue in healthy adults.
In the 1990s, the Air Resources Board implemented a reformulated diesel program and a roadside heavy-duty diesel truck inspection program. In 2016, the state began requiring the use of ultra-low-sulfur fuel.
Croes said further reductions of particulate matter from diesel can be achieved by requiring filters for off-road diesel vehicles such as those used on construction sites.
However, any future significant decline in particulate matter will be tied to changing practices in the shipping and rail industries, both industries where emissions are controlled at the federal level. The ongoing regulation of trucks and buses has reduced their emissions to the point that other diesel sources such as trains and ships now dominate overall emissions.
Edward Ortiz: 916-321-1071, @edwardortiz