Emissions Uncertainty: Focusing on NOx Emissions from Combustion Sources
Emily Wisner, Alissa Anderson, Colin Geisenhoffer, Brody Heffner and Michael Shaw, NC State University
Emission factors are important for estimating and characterizing emissions from sources of air pollution. An emission factor is a representative value that attempts to relate the quantity of a pollutant released to the atmosphere with an activity associated with the release of that pollutant. These factors are usually expressed as the weight of pollutant divided by a unit weight, volume, distance, or duration of the activity emitting the pollutant (e. g., kilograms of particulate emitted per mega gram of coal burned). Such factors facilitate estimation of emissions from various sources of air pollution. In most cases, these factors are simply averages of all available data of acceptable quality, and are generally assumed to be representative of long-term averages for all facilities in the source category (i. e., a population average). The general equation for emission estimation is: E = A x EF x (1 - ER/100). Where: E=Emissions, A=Activity Rate, EF=Emissions Factor, and ER=overall reduction efficiency, %. The objectives of this project are to: (1) Verify the NOx emission factors from combustion sources with currently available continuous emission monitoring data; (2) Develop quantitative uncertainty indicators for A through E rated emission factors on NOx emissions from combustion sources; and (3) Determine the limitations of applying these quantitative uncertainty indicators to other pollutant and source types. We will present comparisons of existing NOx emission factors with revised factors based upon the hourly NOx data collected at all utility plants for the last ten years for all 53 SCC codes for three different fuel types – coal oil and gas.