U.S. national PM2.5 Chemical Speciation Monitoring Networks-CSN and IMPROVE: description of networks.

The US. EnvironmentalProtection Agency (EPA) initiated the national PM2.5 Chemical Speciation Monitoring Network (CSN) in 2000 to support evaluation of long-term trends and to better quantify the impact of sources on particulate matter (PM) concentrations in the size range below 2.