Tetra Tech Inc.
December 2013
Abstract
Particulate matter (PM) emission factors in US EPA’s AP-42 publication for gas-fired combustion sources and large stationary diesel engines were evaluated against more recent data. For gas-fired turbines and external combustion sources, dilution sampling has yielded PM emission factors that are more than an order of magnitude lower than the AP-42 emission factors (determined using US EPA reference test methods). At these low levels, results of the US EPA reference methods are heavily influenced by artifacts in the acetone rinse and excessive conversion of SO2 to sulfate in the impingers; US EPA is currently using the dilution sampling results to estimate emissions from these sources in its National Emissions Inventory. Emissions from spark-ignition gas-fired reciprocating engines are higher, and the EPA reference methods are not as influenced by the detection limit or sulfate issues; however, dilution sampling methods result in PM emission factors for that are lower by approximately a factor of two. For these sources, PM emissions are predominantly organic compounds and the difference between the methods can be attributed to differences in the extent to which they condense organic material. For large stationary diesel engines, emissions data can be highly variable as a function of changes in engine technology and fuel sulfur content and engine duty cycle, such that a single emission factor for a large and varied population of such engines is not recommended; however, for purposes of identifying emissions from specific engines, the use of manufacturer certification data (which are also obtained using dilution sampling methods) is recommended. Remaining data gaps are identified and a test plan for filling those gaps is identified.