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

Abstract

In urban environments, where nitrogen oxide (NO_x = 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 NO_x 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/NO_x 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, NO_x, 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. NO_x emission factors, calculated using the carbon balance method, were 3.41 ± 0.24 and 4.69 ± 0.32 g NO_x 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.

This study assesses vehicle emissions in Los Angeles and Las Vegas, analyzing nitrogen oxides, greenhouse gases, and volatile organic compounds. It provides insights into emission profiles, enhancing our understanding of urban air quality challenges.