On-road ammonia emissions characterized by mobile, open-path measurements

Area of Science:

• Environmental Science
• Atmospheric Chemistry
• Transportation Emissions

Background:

• Ammonia (NH3) is a critical precursor to atmospheric fine particulate matter, influencing regional air quality and climate change.
• Vehicle emissions contribute substantially to urban NH3 levels, necessitating accurate measurement and inventorying.

Purpose of the Study:

• To develop and utilize a mobile platform for measuring on-road emissions of NH3, CO, and CO2 from passenger vehicles.
• To quantify on-road NH3 emission factors (EFs) and emission ratios in New Jersey and California.
• To investigate the influence of driving conditions and road gradients on NH3 emissions.

Main Methods:

• A custom mobile measurement platform was deployed on a passenger car.
• Conducted 87 hours of on-road measurements covering 4500 km in New Jersey and California.
• Utilized open-path sensing technology to measure NH3, CO, and CO2 concentrations.

Main Results:

• Average on-road NH3 EF in California was 0.49 ± 0.06 g/kg fuel, consistent with prior studies.
• The mean on-road NH3:CO emission ratio was 0.029 ± 0.005, with no significant difference between states.
• NH3 EFs increased with road gradient and were higher in stop-and-go and high-speed conditions, with a minimum around 70 km/h.

Conclusions:

• Mobile, open-path measurements offer a valuable method for understanding urban and suburban on-road NH3 emissions.
• Findings suggest potential underestimation of on-road NH3 emissions in existing New Jersey and California inventories.
• The study highlights the significant impact of driving conditions on vehicle NH3 emissions.