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
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