Impacts of On-Road Vehicular Emissions on U.S. Air Quality: A Comparison of Two Mobile Emission Models (MOVES and FIVE)

Abstract

On-road vehicles are significant contributors to air pollution globally, particularly to nitrogen oxides (NO_x) and ozone (O₃). Quantifying their contribution to air quality is crucial to understanding the trends of vehicle emissions as low- and “zero” emission vehicles join the fleet. Modeling on-road emissions is complex due to various factors like fleet activities, traffic patterns, and meteorological conditions. We compare on-road emissions from two mobile models: the National Oceanic and Atmospheric Administration Fuel-based Inventory of Vehicle Emission (FIVE) and the US Environmental Protection Agency Motor Vehicle Emission Simulator (MOVES), finding they contribute 4%–33% to volatile organic compounds (VOCs), NO_x, and fine particulate matter (PM_2.5) in the contiguous United States (CONUS). Using a regional chemical transport model, we assess air quality effects under different emission scenarios. Both emission data sets yield satisfactory performance, with MOVES showing lower biases in ozone (O₃) and PM_2.5 over CONUS, while FIVE performs better at city scales due to higher urban NO_x emissions. In January, on-road emissions increased surface O₃ over western and southern US by up to 9.1%–13.1% but decreased by 2.5% over the northeastern US, while PM_2.5 predictions vary across the US (−85% to 24%). In July, on-road emissions elevate O₃ and PM_2.5 concentrations by 15%–20% across CONUS, except in some west coast cities. They also greatly contribute to nitrogen dioxide (NO₂) by more than 80% near roads and in urban areas. This study highlights the significant impact of on-road emissions on urban air quality and provides insights for improving air quality forecasting and management.