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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/acp-2018-378
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
08 May 2018
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).
Effectiveness of Ammonia Reduction on Control of Fine Particle Nitrate
Hongyu Guo1, Rene Otjes2, Patrick Schlag3,4,a, Astrid Kiendler-Scharr4, Athanasios Nenes1,5,6,7, and Rodney J. Weber1 1School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332, USA
2Energy Research Centre of the Netherlands (ECN), Petten, the Netherlands
3Utrecht University, Utrecht, the Netherlands
4Institute for Energy and Climate Research (IEK-8): Troposphere, Forschungszentrum Jülich, Jülich, Germany
5School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA
6Institute for Chemical Engineering Sciences, Foundation for Research and Technology – Hellas, Patras, 26504, Greece
7Institute for Environmental Research and Sustainable Development, National Observatory of Athens, P. Penteli, Athens, 15236, Greece
anow at: University of Sao Paulo, SP, Brazil
Abstract. In some regions, reducing aerosol ammonium nitrate (NH4NO3) concentrations may substantially improve air quality. This can be accomplished by reductions in precursor emissions, such as nitrogen oxides (NOx) to lower nitric acid (HNO3) that partitions to the aerosol, or reductions in ammonia (NH3) to lower particle pH and keep HNO3 in the gas phase. Using the ISORROPIA-II thermodynamic aerosol model and detailed observational datasets, we explore the sensitivity of aerosol NH4NO3 to gas phase NH3 and NOx controls for a number of contrasting locations, including Europe, the US, and China. NOx control is always effective, whereas the aerosol response to NH3 control is highly nonlinear and only becomes effective at a thermodynamic “sweet spot”. The analysis provides a conceptual framework and fundamental evaluation on the relative value of NOx versus NH3 control. We find that regardless of the locations examined, it is only when ambient particle pH drops below approximately 3 that NH3 reduction leads to an effective response in PM2.5 mass. The required amount of NH3 reduction to efficiently decrease NH4NO3 at different sites is assessed. Owing to the linkage between NH3 emissions and agricultural productivity, substantial NH3 reduction required in some locations may not be feasible. Finally, controlling NH3 emissions to increase aerosol acidity and evaporate NH4NO3 will have other effects, beyond reduction of PM2.5 NH4NO3, such as increasing aerosol toxicity and changing the deposition patterns of nitrogen and trace nutrients.
Citation: Guo, H., Otjes, R., Schlag, P., Kiendler-Scharr, A., Nenes, A., and Weber, R. J.: Effectiveness of Ammonia Reduction on Control of Fine Particle Nitrate, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2018-378, in review, 2018.
Hongyu Guo et al.
Hongyu Guo et al.

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Short summary
Reduction in ammonia has been proposed as a way to lower fine particle mass and improve air quality. But gas phase ammonia is linked to agricultural productivity. We assess the feasibility of ammonia control at a variety of sites through a rigorous aerosol thermodynamic analysis. We show that aerosol response to ammonia control is highly nonlinear and only becomes effective when ambient particle pH drops below approximately three.
Reduction in ammonia has been proposed as a way to lower fine particle mass and improve air...
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