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Because of U.S. EPA regulatory actions and the National Academies National Research Council suggestions for improvements in the U.S. EPA emissions inventory methods, the U.S. EPA' Office of Transportation and Air Quality (OTAQ) has made a concerted effort to develop instrumentation that can measure criteria pollutant emissions during the operation of on-road and off-road vehicles. These instruments are now being used in applications ranging from snowmobiles to on-road passenger cars to trans-Pacific container ships. For the betterment of emissions inventory estimation these on-vehicle instruments have recently been employed to measure time resolved (1 hz) in-use gaseous emissions (CO₂, CO, THC, NO ) and particulate matter mass (with teflon membrane filter) emissions from 29 non-road construction vehicles (model years ranging from 1993 to 2007) over a three year period in various counties in Iowa, Missouri, and Kansas.

In June 2005, the United States Environmental Protection Agency (USEPA) signed a final rule implementing in-use testing requirements for heavy-duty diesel (HDD) engines. The program requires manufacturers to measure gaseous and particulate matter (PM) exhaust emissions from diesel engines using portable emission measurement systems (PEMS) installed on vehicles. In order to measure PM emissions, a cooperative contract between Sensors, Inc. and the USEPA was commenced to develop a Proportional Particulate Mass Device (PPMD). It is comprised of three key elements: a micro-proportional sampling system (MPS) incorporating an exhaust flow-meter (EFM) and an eight element quartz-crystal microbalance (QCM) to measure particulate mass. Evaluation of the exhaust flow meter (EFM) at third-party facilities have shown that the mass emission data and flow data produced with the EFM correlates extremely well with traditional (non-portable) constant volume sampling (CVS) certification systems.