Investigating the Uncertainty in EPA's Nonroad Compression Ignition Emission Factors
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Date
2022-05
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The Ohio State University
Abstract
This study investigates the uncertainty in EPA nonroad compression ignition (CI) emission factors with a focus on construction equipment. Specifically, this study examines the variability in the EPA's average annual predicted NOx, CO, and PM2.5 emissions from the United States construction fleet. A specific focus on construction is taken to better understand worker exposure to different pollutants, as construction workers face increased health risks. To determine such variability, relevant secondary data, including EPA nonroad CI emission factors and literature study emission factors for nonroad diesel construction vehicles, is compiled. Once data compilation is complete, MATLAB scripts are created to calculate EPA and literature study predicted annual emissions from the United States construction fleet. The MATLAB scripts use Monte Carlo simulations to calculate a representative distribution of annual emissions. Finally, the EPA and literature study predicted annual emissions are compared to determine the variability in EPA's predicted emissions. Ultimately, it was found that the EPA underpredicted average NOx emissions, having an error of 13%. The EPA overpredicted average CO and PM2.5 emissions, with an error of 170% and 190%, respectively. These results suggest that the EPA does have significant variability in their predicted annual emissions for construction equipment. The overestimation paired with the increased health risks construction workers face suggests a need for revision of OSHA exposure limits. Additionally, such overestimating may cause increased emission standards which in turn may drive technological advancements. However, increased emission regulations create contrasting implications, depending on the stakeholder (e.g., construction workers vs engine manufacturers).
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Keywords
Emission Factors, Compression Ignition, EPA, Construction Equipment, Emissions, Uncertainty