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Journal article
Vehicle emission ratios of HCN and HONO measured near a highway in Meridian, Idaho
Atmospheric environment, v 359, 121379
15 Oct 2025
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Abstract
Much effort is spent by the air pollution and atmospheric science communities on quantifying pollutant emissions as they are used as inputs in air quality models and assist in the interpretation of atmospheric measurements at field sites. Nitrogen oxides (“NOx”, defined as the sum of nitric oxide NO and nitrogen dioxide NO2), nitrous acid (HONO), and hydrogen cyanide (HCN) are all byproducts of combustion processes. While NOx emissions from on-road vehicles have been extensively studied, vehicle emissions of HONO and especially HCN are not as well quantified. Enhancing our knowledge of direct HCN and HONO emissions is essential because HONO is an important precursor to the hydroxyl radical (OH), thereby playing a critical role in atmospheric oxidation, and HCN is toxic, long-lived in the atmosphere, and used as a tracer for biomass burning. In this manuscript, we present measurements of HCN and HONO made using an iodide-adduct chemical ionization mass spectrometer (CIMS) during August of 2019 near a highway in Meridian, Idaho. Vehicle emission ratios of HCN and HONO with respect to NOx (i.e., ΔHCN/ΔNOx and ΔHONO/ΔNOx) are reported as well as emission ratios of HCN and NOx with respect to carbon monoxide (CO) (i.e., ΔHCN/ΔCO and ΔNOx/ΔCO). Observed emission ratios were quite variable and determined for select highway influenced periods during the nighttime and early morning (prior to sunrise) located typically 200–500 s downwind of the major interstate highway. We report average values of 5.3 and 1.13 ppbv ppmv−1 for ΔHCN/ΔNOx and ΔHCN/ΔCO, respectively. The average ΔHONO/ΔNOx value - 9.8 ppbv ppmv−1 - falls within the range of reported literature values though it is somewhat higher than the commonly used value of 8 ppbv ppmv−1.
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Details
- Title
- Vehicle emission ratios of HCN and HONO measured near a highway in Meridian, Idaho
- Creators
- Andrew John Lindsay - Drexel University, ChemistryKyle G Banecker - Drexel University, ChemistryBrigitte Marie Weesner - Drexel University, ChemistryEzra Wood (Corresponding Author) - Drexel University, Chemistry
- Publication Details
- Atmospheric environment, v 359, 121379
- Publisher
- Elsevier
- Number of pages
- 9
- Grant note
- NOAA: NA17OAR4310102 NSF: AGS 2002928 University of Washington
We acknowledge financial support from NOAA grant NA17OAR4310102 and NSF grant AGS 2002928. We gratefully thank Edward Jolly and the Idaho Department of Environmental Quality for hosting our measurements at their Saint Lukes Meridian site, logistical support, and providing supporting gaseous and meteorological data. We thank Dan Jaffe (University of Washington) for project coordination. We thank Michael Waring for the loan of the ozone calibration source.
- Resource Type
- Journal article
- Language
- English
- Academic Unit
- Chemistry
- Web of Science ID
- WOS:001529335300002
- Scopus ID
- 2-s2.0-105009689016
- Other Identifier
- 991022061454204721
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- Web of Science research areas
- Environmental Sciences
- Meteorology & Atmospheric Sciences