
The reduction of summer sulfate and switch from summertime to wintertime PM2.5 concentration maxima in the United States
Keywords: Air quality; Fine particulate matter; PM2.5; Sulfate; Nitrate; Organic carbon; AQS; Air quality system; CSN; Chemical Speciation Network; EPA; Environmental Protection Agency; FEM; Federal Equivalent Method; FRM; Federal Reference Method; IMPROVE; Interag