As part of the PM2.5 National Ambient Air Quality Standards (NAAQS) review completed in 1997, EPA established a PM2.5 Chemical Speciation Network (CSN) consisting of Speciation Trends Network (STN) sites and supplemental speciation sites. The CSN is a component of the National PM2.5 Monitoring Network, whose goal is to establish if the NAAQS are being attained. However, CSN data are not used for attainment or nonattainment decisions, but are intended to complement the activities of the larger gravimetric PM2.5 measurement network component. For more information, visit the Chemical Speciation Network (CSN) website.