2011. United States. Environmental Protection Agency. Region IX. This polygon shapefile shows designated areas for particulate matter < 10 microns according to the 24-Hour National Ambient Air Quality Standard... California. Air Resources Board.
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2013. United States. Environmental Protection Agency. Region IX. This polygon shapefile contains nonattainment areas for particulate matter < 10 microns. Nonattainment areas are geographic areas which have not... United States. Environmental Protection Agency. Region IX.