| Ammonia emissions from mobile sources are an important contributor to secondary particulate matter (PM) levels in the atmosphere. It is therefore essential to develop an accurate estimation of ammonia emissions from mobile sources in order to promulgate effective PM reduction strategies, especially in the South Coast Air Basin (SoCAB) where mobile source activity is much higher compared to other areas of the nation. In this study we generated a standard operating procedure (SOP) for measurement of ammonia emissions from vehicles on a chassis dynamometer using Fourier Transform Infrared Spectroscopy (FTIR). We used the SOP to conduct 121 emissions tests on 41 vehicles acquired from the greater Los Angeles area. The test results were then examined to determine the effects of several key variables on ammonia emissions. These variables included vehicle type, driving cycle/mode, emissions technology, fuel type, vehicle repair status, ammonia precursor emissions (i.e. CO and NOx) and odometer readings/model year as a proxy for catalyst age. The mean ammonia emissions factor was 46 mg/km (sigma = 48 mg/km) for the vehicle fleet, which was qualitatively similar to emissions factors reported in previous research. Although we were not able to establish any statistical significance for our results due to the limited sample size, the results of this study suggested the highest ammonia emitters are likely to possess the following characteristics: medium-duty vehicles, older emissions technologies, mid-range odometer readings, and higher CO emissions. In addition, vehicles subjected to aggressive driving conditions were likely to be higher ammonia emitters. As vehicle population and vehicle activity in SoCAB increases, it is likely mobile sources will become a larger contributor to total ammonia emissions. As a result, air quality regulators may have to focus more effort on reducing ammonia emissions from mobile sources in the future. |
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