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    Author(s): Mark E. Fenn; Andrzej Bytnerowicz; Susan L. Schilling; Dena M. Vallano; Erika S. Zavaleta; Stuart B. Weiss; Connor Morozumi; Linda H. Geiser; Kenneth Hanks
    Date: 2018
    Source: Science of The Total Environment. 625: 909-919
    Publication Series: Scientific Journal (JRNL)
    Station: Pacific Southwest Research Station
    PDF: Download Publication  (4.0 MB)


    We provide updated spatial distribution and inventory data for on-road NH3 emissions for the continental United States (U.S.) On-road NH3 emissions were determined from on-road CO2 emissions data and empirical NH3:CO2 vehicle emissions ratios. Emissions of NH3 from on-road sources in urbanized regions are typically 0.1–1.3 t km− 2 yr− 1 while NH3 emissions in agricultural regions generally range from 0.4–5.5 t km− 2 yr− 1, with a few hotspots as high as 5.5–11.2 t km− 2 yr− 1. Counties with higher vehicle NH3 emissions than from agriculture include 40% of the U.S. population. The amount of wet inorganic N deposition as NH4+ from the National Atmospheric Deposition Program (NADP) network ranged from 37 to 83% with a mean of 58.7%. Only 4% of the NADP sites across the U.S. had < 45% of the N deposition as NH4+ based on data from 2014 to 2016, illustrating the near-universal elevated proportions of NH4+ in deposition across the U.S. Case studies of on-road NH3 emissions in relation to N deposition include four urban sites in Oregon and Washington where the average NH4-N:NO3-N ratio in bulk deposition was 2.3. At urban sites in the greater Los Angeles Basin, bulk deposition of NH4-N and NO3-N were equivalent, while NH4-N:NO3-N in throughfall under shrubs ranged from 0.6 to 1.7. The NH4-N:NO3-N ratio at 7–10 sites in the Lake Tahoe Basin averaged 1.4 and 1.6 in bulk deposition and throughfall, and deposition of NH4-N was strongly correlated with summertime NH3 concentrations. On-road emissions of NH3 should not be ignored as an important source of atmospheric NH3, as a major contributor to particulate air pollution, and as a driver of N deposition in urban and urban-affected regions.

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    Fenn, Mark E.; Bytnerowicz, Andrzej; Schilling, Susan L.; Vallano, Dena M.; Zavaleta, Erika S.; Weiss, Stuart B.; Morozumi, Connor; Geiser, Linda H.; Hanks, Kenneth. 2018. On-road emissions of ammonia: An underappreciated source of atmospheric nitrogen deposition. Science of The Total Environment. 625: 909-919.


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    Three-way catalytic converter, Nitrogen form, Transport sector, Heavy-duty vehicles, Emissions trends, Urban air pollution

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