Exhaust Emission Factors for Nonroad Engine Modeling-Spark Ignition

Purpose This report describes and documents exhaust emission factors used for spark ignition (SI) engines in EPA's NONROAD emission inventory model. It covers emission factors for engines powered by gasoline, natural gas and liquefied petroleum gas. EPA expects to recalculate most SI emission factors prior to release of the final version of the NONROAD model. This report describes the emission factors that will be used for the draft version of the model and lists the data sources that will be considered when calculating new emission factors for the final model. When complete, the final emission factors will be similarly documented and distributed for stakeholder review. Additional EPA reports will describe other issues relating to emission factors including NONROAD emission factors for evaporative emissions, crankcase emissions, spillage and other non-exhaust emissions (NR-012), adjustments to emission rates due to variations in fuel and temperature (NR-001), speciation of hydrocarbon emissions (NR-002), and adjustments to emission rates as equipment deteriorates due to time and use (NR-011). Emission factors for compression ignition (diesel) engines are covered in a separate report (NR-009). Introduction The U.S. EPA's NONROAD model computes county-level emission inventories for nonroad engines. These calculations rely on emission factors-estimates of the amount of pollution emitted by a particular type of equipment during a unit of use. Typically emission factors for nonroad sources are reported in grams per horsepower-hour, but they also may be reported in grams per mile, grams per hour, grams per gallon, etc. nr-010b.wpd 2 This report begins by describing emission factors used in prior models. It then briefly describes our plans for pre-controlled and controlled SI exhaust emission factors in the draft and final versions of NONROAD. Appendix A provides information on the sources of emission factors. Appendix B has two parts: (1) a large spreadsheet that lists the numerical value of emission factors that have been used in prior inventories and that we intend to use for the draft version of NONROAD, and (2) a guide to using the spreadsheet. Appendix C explains how NONROAD uses "technology groups" to account for changes in emisssion factors over time. The pollutants covered by this report include exhaust total hydrocarbons (HC), carbon monoxide (CO), oxides of nitrogen (NOx), total particulate matter (PM), and brake specific fuel consumption (BSFC). For nonroad engines all PM emissions are assumed to be smaller than 10 microns (PM10), and 92% of the PM from gasoline and diesel fueled …