Constraining Ammonia Emissions in Vehicle Plumes Utilizing Nitrogen Stable Isotopes

Abstract

Abstract. Vehicle emissions have been identified as an important urban source of ammonia (NH3). However, there are large uncertainties regarding the contribution of vehicle emissions to urban NH3 budgets, as well as its role in spatiotemporal fine particulate matter (PM2.5) formation and nitrogen (N) deposition patterns. The N stable isotopic composition (δ15N) may be a useful observational constraint to track NH3 emission sources and chemical processing, but previously reported vehicle δ15N(NH3) emission signatures have reported a wide range of values, indicating the need for further refinement. Here we have characterized δ15N(NH3) spatiotemporal variabilities from vehicle plumes in stationary and on-road measurements in the US and China using a laboratory- and field-verified NH3 collection technique shown to be accurate for characterizing δ15N(NH3) on the order of hourly time resolution. Significant spatial and temporal δ15N(NH3) variabilities were observed and suggested to be driven by vehicle fleet composition and influences from NH3 dry deposition on tunnel surfaces. The reactive NH3 sink associated with particulate ammonium (pNH4+) formation was found to have a minimal impact on the vehicle plume δ15N(NH3) measurements due to the vast majority of NHx (= NH3 + pNH4+) residing as NH3. Overall, a consistent δ15N(NH3) signature of 6.6 ± 2.1 ‰ (x ± 1σ; n = 80) was found in vehicle plumes with fleet compositions typical of urban regions. Overall, these measurements constrain the δ15N(NH3) urban traffic plume signature, which has important implications for tracking vehicle NH3 in urban-affected areas.

Atmospheric Ammonia in Beijing during the COVID-19 Outbreak: Concentrations, Sources, and Implications

“…It should be noticed that sampling methods (active and passive samplers) also play a considerable role in the measured values of δ 15 N-NH 3 . 47 Walters et al 26 and Pan et al. 47 confirmed a low bias of passive samplers in δ 15 N-NH 3 observations compared to active samplers due to the isotopic effects of gas diffusion, while no significant differences were found between different passive samplers.…”

“…However, particulate NH 4 + concentrations were not measured at the four on-road sites. For site 3 (tunnel interior), the f value was set at 0.044 on the basis of Walter et al, 26 who reported f was extremely low in the tunnel. For the other three on-road sites (sites 1, 2, and 4), we performed a sensitivity analysis in which we modeled f values ranging from 0.0 to 1.0 to estimate the expected δ 15 N-NH x .…”

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

“…Data availability. Data presented in this article are available on the Brown Digital Repository at https://doi.org/10.26300/q3h4-7s93 (Walters, 2020).…”

Effects of Urban Topography and Traffic Emissions of Ultrafine Particulate Matter, Reactive Nitrogen Species, and Ozone in Greater Los Angeles Area

“…23 However, the converters often over-reduce to NH3 which has contributed to a high rise in the nitrogen budget, instead of a decline. 24,25 Ammonia formation through this method also increases particle nucleation by several orders of magnitude. 26 Reduction of NOx emissions from both two-and three-way catalytic converters in vehicles have been shown to increase NHx (= NH3 + NH4 + ) emissions by approximately 15% in the atmosphere.…”

“…26 Reduction of NOx emissions from both two-and three-way catalytic converters in vehicles have been shown to increase NHx (= NH3 + NH4 + ) emissions by approximately 15% in the atmosphere. 27,28 Using Stable isotopes of Nitrogen ( 15 N, 14 N) as a tool to trace original sources of nitrogen pollutants through ratios 15 N/ 14 N sample compared directly to the international isotopic standard for nitrogen (atmospheric air) gives a number in a unit of per mil (‰) (δ 15 24,29,30,31,32,33,34,35 The partitioning of NHx between the gas, solid, and aqueous phases is driven by thermodynamic equilibrium that depends on the relative humidity, temperature, and particle chemical composition, making the separation of each phase(speciation) difficult. 36 Isotopic analysis for source tracing has shown great promise in terms of requisite time resolution, quantitative collections of concentration and no fractionation upon collection for collection of NHx(g) and pNH4 + with a reproducibility of ≤1.5‰ for application in multiple field environments.…”