US EPA has posted a Conceptual Method for Determination of Total Vapor Phase Mercury Emissions from Coal-Fired Combustion Sources . This conceptual method is the prototype of a future air pollution emission test method to be proposed and promulgated through notice and comment rulemaking. The method is intended for use as a reference test method for conducting relative accuracy testing (RATA)of mercury continuous emission monitoring systems (CEMS) installed at coal-fired combustion sources, as well as for measurement of mercury emissions from stationary sources.