The reduction of summer sulfate and switch from summer to winter PM2.5 concentration maxima in the U.S.
These four files each contain 24-hour PM2.5 concentrations collected between 2000-2015. 

This dataset is associated with the following publication:
Chan, E., B. Gantt, and S. McDow. The reduction of summer sulfate and switch from summertime to wintertime PM2.5 concentration maxima in the United States.   ATMOSPHERIC …