Fig. 1. Annual average ground-level PM2.5 concentration (mg m"3
) from U.S. sources attributable to combustion emissions from (a) electric power generation; (b) industry; (c)
commercial and residential sources; (d) road transportation; (e) marine transportation; (f) rail transportation; (g) sum of all combustion sources; (h) all sources (baseline case for
this study). A different scale is adopted for (aef) and (geh).