On-Road Measurements of Nitrogen Oxides, CO, CO2, and VOC Emissions in Two Southwestern U.S. Cities ACS ES&T Air

In urban environments, where nitrogen oxide (NOx = NO2 + NO) and volatile organic compound (VOC) concentrations are elevated, complex photochemical reactions lead to increased tropospheric ozone production and other forms of air pollution. On-road vehicles persist as a primary contributor to NOx and VOC emissions in urban areas. This study deployed high time resolution, high sensitivity instruments to sample on-road vehicle emissions in Los Angeles, CA (LA) and Las Vegas, NV (LV) in the summer of 2021. The total oxidant approach was used to estimate average NO2/NOx values from vehicle plumes, which were 6.3 ± 0.5 and 5.9 ± 0.4% for LA and LV, respectively. Ratios of aromatic VOCs to three different combustion tracers, NOx, CO, and CO2, were analyzed and found to be greater for toluene (C7) than benzene (C6), but decreased with carbon number for C7–C10 aromatics. NOx emission factors, calculated using the carbon balance method, were 3.41 ± 0.24 and 4.69 ± 0.32 g NOx per kg of fuel burned for LA and LV, respectively, consistent with values extracted from the Fuel-based Inventory of Vehicle Emissions (FIVE). These results provide insights into on-road emission profiles and support long-term observations of pollutants emitted from motor vehicles. Grant no. NA17OAR4320101 Grant no. NA22OAR4320151