Characteristics and Relevance of Method-defined Condensable Particulate Matter Formation from Major Stationary Sources

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

     Abstract Number: 279
     Working Group: Aerosol Chemistry

Abstract
In the atmosphere, condensable particulate matter (CPM) forms when stack exhaust cools and dilutes resulting in organic and inorganic gasses quickly reacting to form particulate and/or 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 and is therefore very relevant to human health for fenceline communities. EPA’s Method 202 (40 CFR Part 51, Appendix M), an impinger-based CPM measurement method, is the agency’s existing recommended methodology for state, local, and tribal agencies to use for measuring CPM. However, stakeholders have raised concerns over potential measurement bias. Dilution-based methods, like Other Test Method 37 (OTM-37) have also been used to estimate CPM mass. However, studies showing the repeatability and actionability of OTM-37, attributes paramount for a compliance method, are lacking. Both methods provide users with method-defined CPM mass. The relationship between the two methods is unknown and there are questions regarding the relevance of method-defined CPM mass to real-world, near-stack CPM formation. While this relationship is not necessary for compliance, it is paramount for understanding local and regional air quality issues and determining the most effective paths for reducing PM. For the past several years, EPA has been conducting laboratory experiments using initial conditions relevant to stack emissions to investigate the formation of CPM in the Method 202 and OTM-37 sampling trains. While results from these studies provide insight into the chemistry and variability of CPM formation within each respective sampling train, the studies lack a connection to real-world CPM formation. This work highlights the importance of developing an atmospherically relevant CPM formation method and establishes the need for a better understanding of near-stack PM formation, possibly via coupling in-stack measurements with in-plume measurements.