The U.S. Environmental Protection Agency (EPA) has issued amendments to the new source review (NSR) rules under the Clean Air Act (CAA) to clarify how applicants must measure and account for condensable particulate matter. According to EPA’s fact sheet about the revised NSR rules, emission stacks do not directly release condensable particulate matter (PM) as a solid or liquid. “Instead gaseous emissions such as sulfuric acid mist, ammonium sulfate, and certain metal vapors condense upon cooling and dilution in the ambient air to form solid or liquid particles,” states the agency, which previously established national ambient air quality standards (NAAQS) for PM less than 2.5 micrometers in diameter (PM2.5) and PM less than 10 micrometers in diameter (PM10).

Correcting aspects of EPA’s 2008 NSR rule, the latest final rule still requires facilities to calculate condensable PM as PM10 or PM2.5 as appropriate but removes an “inadvertent” requirement in the PM2.5 implementation rule that called for condensable PM to be included in measurements of “particulate matter emissions.” This latter requirement apparently resulted in the consideration of condensable PM2.5 as part of total particulate matter, a measurement relevant under the CAA’s new source performance standards but not under the NSR program. The revision clarifies that condensable PM2.5 is counted in connection with a facility’s PM2.5 demonstration under the NSR process.