San Francisco Chronicle: California grossly miscalculated pollution levels in a scientific analysis used to toughen the state’s clean-air standards, and scientists have spent the past several months revising data and planning a significant weakening of the landmark regulation, The Chronicle has found. 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 …