Characteristics of Condensable Particulate Matter Formation in the EPA Method 202 Sampling Train

PAUL VAN ROOY, Dave Nash, Jason Dewees, Ned Shappley, Walter Lin, Peter Kariher, US EPA

     Abstract Number: 711
     Working Group: Instrumentation and Methods

Abstract
In the atmosphere, condensable particulate matter (CPM) forms when stack exhaust cools resulting in organic and inorganic gasses condensing on to existing solid particulate or liquid droplets. As particulate controls become more effective at removing filterable particulate matter, CPM mass is quickly becoming the dominant fraction of measured source emissions. EPA’s Method 202 (40 CFR Part 51, Appendix M) is the recommended methodology for state, local, and tribal agencies to use for measuring CPM. In the Method 202 sampling train, the CPM is collected in dry impingers after filterable PM has been collected. The organic and aqueous fractions of the impingers and an out-of-stack CPM filter are then taken to dryness and weighed. As it exists now, EPA Method 202 provides a method-defined CPM mass. However, stakeholders have raised concerns over potential measurement bias. Additionally, there are questions regarding the relationship between Method 202 determined CPM mass and the actual CPM mass formation in the atmosphere. While this relationship between real-world and method-defined CPM mass is not necessary for compliance, it is paramount for understanding local and regional air quality issues and determining the most efficient and effective paths for reducing PM. For the past several years, EPA has been conducting controlled laboratory experiments to investigate the formation of CPM in the Method 202 sampling train. A wide variety of initial conditions relevant to stack emissions were studied to understand the impact of humidity, precursor concentrations, and general method variability on CPM composition and mass formation in the sampling train.