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 coincidence with the pollutant measurements exhaust flow, engine speed, and in a few cases engine power from the vehicle engine control module have been measured. From these exhaust and engine operation measurements pollutant mass emission rates, mass concentrations, mass per fuel use, and mass per energy (work or brake specific) emissions have been determined. The brake specific emissions were estimated from the engine speed measurements and brake specific fuel consumption (bsfc) curves. There were about 35 tests completed on these 33 vehicles ranging in time from about 10 to 600 minutes with an average test time of about 220 minutes.