“Fingerprinting” Vehicle Derived Ammonia Utilizing Nitrogen Stable Isotopes

Wendell Walters1, Nadia Colombi2 and Meredith Hastings3

Ammonia (NH3) is the primary alkaline molecule in the atmosphere and plays a key role in numerous atmospheric processes that have important implications for human health and climate control.  While agriculture activities dominate the global NH3 budget, there are large uncertainties in the urban NH3 emission inventories.   The analysis of the nitrogen stable isotope composition of NH315N-NH3) might be a useful tool for partitioning NH3 emission sources, as different emission sources tend to emit NH3 with distinctive δ15N signatures or “fingerprints”.  This novel tool may help improve upon urban emission inventories, which could help to improve modeling of important atmospheric processes involving NH3.   However, there is a current lack of δ15N-NH3 measurements of potentially important urban NH3 emission sources, and many of the reported NH3 collection methods have not been verified for their ability to accurately characterize δ15N-NH3

Here we present a laboratory tested method to accurately measure δ15N-NH3 using honeycomb denuders coated with a 2% citric acid solution.   Based on laboratory tests, the NH3 collection device has been optimized under a variety of conditions.  Near quantitative NH3 collection is found at a sampling rate of 10 SLPM for NH3 concentrations less than 2 ppmv, and δ15N-NH3 precision is found to be approximately 1.0‰.  This newly developed NH3 collection device for isotopic characterization has been applied to improve our understanding of the δ15N-NH3 signatures from vehicles.  Preliminary results of NH3 collected near a road-side indicate an average δ15N-NH3 of -2.1 ± 1.9‰.  This work is ongoing, and plans are in place to collect NH3 directly from tailpipes and from on-road air.  Our preliminary results indicate that vehicle derived NH3 has a distinctive δ15N signature compared to agricultural and waste emissions; thus, δ15N(NH3) has the potential to be used to understand urban NH3 emission sources.

 

1Brown University, wendellwalters@gmail.com
2University of California Los Angeles, nkcolombi@gmail.com
3Brown University, meredith_hastings@brown.edu