Nitrogen Stable Isotope Composition (δ¹⁵N) of Vehicle-Emitted NO_x

Abstract

The nitrogen stable isotope ratio of NOx (δ(15)N-NOx) has been proposed as a regional indicator for NOx source partitioning; however, knowledge of δ(15)N values from various NOx emission sources is limited. This study presents a detailed analysis of δ(15)N-NOx emitted from vehicle exhaust, the largest source of anthropogenic NOx. To accomplish this, NOx was collected from 26 different vehicles, including gasoline and diesel-powered engines, using a modification of a NOx collection method used by the United States Environmental Protection Agency, and δ(15)N-NOx was analyzed. The vehicles sampled in this study emitted δ(15)N-NOx values ranging from -19.1 to 9.8‰ that negatively correlated with the emitted NOx concentrations (8.5 to 286 ppm) and vehicle run time because of kinetic isotope fractionation effects associated with the catalytic reduction of NOx. A model for determining the mass-weighted δ(15)N-NOx from vehicle exhaust was constructed on the basis of average commute times, and the model estimates an average value of -2.5 ± 1.5‰, with slight regional variations. As technology improvements in catalytic converters reduce cold-start emissions in the future, it is likely to increase current δ(15)N-NOx values emitted from vehicles.

Automated, High-resolution Mobile Collection System for the Nitrogen Isotopic Analysis of NO_x

“…This method of NO x collection for isotopic analysis is unique among existing methods (e.g., passive samplers 6,17 and sulfuric acid and hydrogen peroxide solution 8 ) in that it has been laboratory-and field-verified with respect to field applicability, reproducibility, sample solution stability, and efficiency of collection under a range of field conditions. This novel method is unique in its capabilities to actively collect NO x in field environments for isotopic analysis at ambient concentrations at a 30-120 min time resolution.…”

“…In addition to methodological issues 4,17 , a variety of different types of air sampling may also contribute to differences in the reported ranges for isotope values associated with the same source. For example, isotopic signatures associated with vehicle emissions of NO x have been suggested based on collections at near-road sites 5 , in traffic tunnels 6 , and directly from the tailpipes of vehicles 7,8 . Furthermore, previous methods have time resolutions of 24 h at best, and significant changes in ambient NO x concentrations are observed on hourly (or shorter) timescales , is further validated through the demonstration of its collection efficiency under changing NO x and meteorological conditions in the field, the test of solution stability and ammonia interferences, and the substantiation of its reproducibility in urban environments.…”

NO<sub>2</sub> and HCHO measurements in Korea from 2012 to 2016 from Pandora spectrometer instruments compared with OMI retrievals and with aircraft measurements during the KORUS-AQ campaign

“…An FTIR analysis of automobile exhaust shows that NO is emitted at 127 ppm, NO 2 at 1.6 ppm, HCHO at 39 ppm, and CH 3 OH at 139 ppm as part of the main emissions containing H 2 O (144 ppm) and CO 2 (122 ppm) (https://tools.thermofisher.com/content/sfs/ brochures/D10248~.pdf, last access: 31 July 2018; see also Walters et al, 2015).…”

Efficacy of passive sampler collection for atmospheric NO2 isotopes under simulated environmental conditions

“…This method has been described in detail by Walters et al . and Felix et al . Briefly, samples from the tank were collected in evacuated 1‐L borosilicate bulbs (Sigma Aldrich, St. Louis, MO, USA) which were connected to tubing attached to the reference gas tank.…”

“…The conservation of the nitrogen atom between NO x sources and sinks allows for the determination of NO x source apportionments to ecosystems using δ 15 N signatures. The δ 15 N values of NO x from anthropogenic and natural sources have recently become more widely documented and span a large range (–49 to +26 ‰), depending on the NO x emission source . In addition, recent experimental and modeling efforts have focused on determining kinetic and equilibrium isotope fractionation associated with the tropospheric oxidation of NO x to nitrate (NO 3 – ) to facilitate tracing the land‐atmosphere reactive NO x cycle using δ 15 N signatures .…”