It appears that California may have erred when it calculated pollution levels used to support the state's clean air standards - by 340%. According to the San Francisco Chronicle: "The pollution estimate in question was too high - by 340 percent, according to the California Air Resources Board, the state agency charged with researching and adopting air quality standards. The estimate was a key part in the creation of a regulation adopted by the Air Resources Board in 2007, a rule that forces businesses to cut diesel emissions by replacing or making costly upgrades to heavy-duty, diesel-fueled off-road vehicles used in construction and other industries."