Distributions of PM₁₀ and PM_2.5,1999–2005, surveillance-oriented sites from contiguous U.S. region.

Abstract

a<p>Following the promulgation of the National Ambient Air Quality Standard for PM_2.5 in 1997, routine collection of PM_2.5 was implemented in 1999. No attempt was made to convert PM₁₀ concentrations to PM_2.5, which requires a scaling factor based on a presumptive proportion of PM_2.5 in the PM₁₀ mass.</p>b<p>Sites describe unique sampling points indicated by longitude/latitude. Those providing no geodetic datum information were not included.</p>c<p>While PM was typically measured at a frequency of every six days or higher, many sites took daily sampling.</p