On-Road
Ammonia Emissions Characterized by Mobile,
Open-Path Measurements
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Abstract
Ammonia (NH<sub>3</sub>) is a key
precursor species to atmospheric
fine particulate matter with strong implications for regional air
quality and global climate change. NH<sub>3</sub> from vehicles accounts
for a significant fraction of total emissions of NH<sub>3</sub> in
urban areas. A mobile platform is developed to measure NH<sub>3</sub>, CO, and CO<sub>2</sub> from the top of a passenger car. The mobile
platform conducted 87 h of on-road measurements, covering 4500 km
in New Jersey and California. The average on-road emission factor
(EF) in CA is 0.49 ± 0.06 g NH<sub>3</sub> per kg fuel and agrees
with previous studies in CA (0.3–0.8 g/kg). The mean on-road
NH<sub>3</sub>:CO emission ratio is 0.029 ± 0.005, and there
is no systematic difference between NJ and CA. On-road NH<sub>3</sub> EFs increase with road gradient by an enhancement of 53 mg/kg fuel
per percentage of gradient. On-road NH<sub>3</sub> EFs show higher
values in both stop-and-go driving conditions and freeway speeds with
a minimum near 70 km/h. Consistent with prior studies, the on-road
emission ratios suggest a highly skewed distribution of NH<sub>3</sub> emitters. Comparisons with existing NJ and CA on-road emission inventories
indicate that there may be an underestimation of on-road NH<sub>3</sub> emissions in both NJ and CA. We demonstrate that mobile, open-path
measurements provide a unique tool to help quantitatively understand
the on-road NH<sub>3</sub> emissions in urban and suburban settings