# Characterizing the spatiotemporal nitrogen stable isotopic composition of ammonia in vehicle plumes

Vehicle emissions have been identified as an important urban source of ammonia (inline-formulaNH3). However, there are large uncertainties regarding the contribution of vehicle emissions to urban inline-formulaNH3 budgets, as well as the role of inline-formulaNH3 in spatiotemporal fine particulate matter (inline-formulaPM2.5) formation and nitrogen (N) deposition patterns. The N stable isotopic composition (inline-formulaδ15N) may be a useful observational constraint to track inline-formulaNH3 emission sources and chemical processing, but previously reported vehicle inline-formulaδ15N(NH3) emission signatures have reported a wide range of values, indicating the need for further refinement. Here we have characterized inline-formulaδ15N(NH3) spatiotemporal variabilities from vehicle plumes in stationary and on-road measurements in the USA and China using an active inline-formulaNH3 collection technique demonstrated to accurately characterize inline-formulaδ15N(NH3) on the order of hourly time resolution. Significant spatial and temporal inline-formulaδ15N(NH3) variabilities were observed and suggested to be driven by vehicle fleet composition and influences from inline-formulaNH3 dry deposition on tunnel surfaces. Overall, a consistent inline-formulaδ15N(NH3) signature of inline-formula6.6±2.1 ‰ (inline-formula $M15inlinescrollmathml\stackrel{normal ‾}{x}±normal 1\mathrm{italic \sigma }$ 33pt11ptsvg-formulamathimge41cf8a8db9b73596012c373bf3f0c65 acp-20-11551-2020-ie00001.svg33pt11ptacp-20-11551-2020-ie00001.png ; inline-formulan=80) was found in fresh vehicle plumes with fleet compositions typical of urban regions. Our recommended vehicle inline-formulaδ15N(NH3) signature is significantly different from previous reports. This difference is due to a large and consistent inline-formulaδ15N(NH3) bias of approximately inline-formula−15.5 ‰ between commonly employed passive inline-formulaNH3 collection techniques and the laboratory-tested active inline-formulaNH3 collection technique. This work constrains the inline-formulaδ15N(NH3) urban traffic plume signature, which has important implications for tracking vehicle inline-formulaNH3 in urban-affected areas and highlights the importance of utilizing verified collection methods for accurately characterizing inline-formulaδ15N(NH3) values.

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Walters, Wendell W. / Song, Linlin / Chai, Jiajue / et al: Characterizing the spatiotemporal nitrogen stable isotopic composition of ammonia in vehicle plumes. 2020. Copernicus Publications.

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