Center for Environmental Research & Technology

CE-CERT Conducts Real-World Study on Ammonia Emissions from Light-Duty Vehicles

By Sara Salsgiver | May 21, 2025

At UC Riverside’s Center for Environmental Research and Technology (CE-CERT), researchers are collecting real-world emissions data on ammonia, a pollutant that contributes to the formation of secondary fine particulate matter (PM2.5), which has known impacts on air quality and human health.

This project, led by CE-CERT Professor Georgios Karavalakis and graduate student Troy Hurren, focuses on measuring ammonia emissions from gasoline-powered light-duty vehicles under typical driving conditions. More than 15 vehicles have been tested to date, ranging from model years 2009 to 2024. The test fleet includes both conventional gasoline and hybrid vehicles to represent the vehicle types found on California’s roads. Each vehicle is driven on a specific route through Riverside that captures a range of real-world driving scenarios.

The team uses a portable emissions analyzer that relies on tunable diode laser spectroscopy to measure ammonia concentration in the exhaust. The analyzer is compact enough to be operated from inside the vehicle, allowing for high-resolution, in-use measurements without affecting the vehicle's performance.

Initial results show that a large portion of ammonia emissions occurs during cold-start conditions, when the engine and emissions control system have not yet reached the ideal operating temperatures. Although cold starts only account for a smaller percentage of the total driving time, they produce a disproportionately high share of ammonia emissions. This suggests that emissions control strategies focused on warm-up periods could have a meaningful impact on reducing the total ammonia output.

Ammonia from vehicle tailpipes is not subject to current emissions standards in the United States. However, the data from this project offer a reference point for regulatory agencies considering whether ammonia limits may be needed in the future. These findings reflect actual driving behavior in typical passenger vehicles and can be used to assess when and how ammonia emissions are most likely to occur.

The study is nearing completion and will contribute to a better understanding of ammonia emissions from light-duty vehicles and help inform future discussions on air quality standards.