Effectiveness of ammonia reduction on control of fine particle nitrate
<p>In some regions, reducing aerosol ammonium nitrate (NH<sub>4</sub>NO<sub>3</sub>) concentrations may substantially improve air quality. This can be accomplished by reductions in precursor emissions, such as nitrogen oxides (NO<sub><i>x</i></su...
Main Authors: | , , , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2018-08-01
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Series: | Atmospheric Chemistry and Physics |
Online Access: | https://www.atmos-chem-phys.net/18/12241/2018/acp-18-12241-2018.pdf |
Summary: | <p>In some regions, reducing aerosol ammonium nitrate
(NH<sub>4</sub>NO<sub>3</sub>) concentrations may substantially improve air quality.
This can be accomplished by reductions in precursor emissions, such as
nitrogen oxides (NO<sub><i>x</i></sub>) to lower nitric acid (HNO<sub>3</sub>)
that partitions to the aerosol, or reductions in ammonia (NH<sub>3</sub>) to
lower particle pH and keep HNO<sub>3</sub> in the gas phase. Using the
ISORROPIA-II thermodynamic aerosol model and detailed observational data sets,
we explore the sensitivity of aerosol NH<sub>4</sub>NO<sub>3</sub> to gas-phase
NH<sub>3</sub> and NO<sub><i>x</i></sub> controls for a number of contrasting
locations, including Europe, the United States, and China. NO<sub><i>x</i></sub> control
is always effective, whereas the aerosol response to NH<sub>3</sub> 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 NO<sub><i>x</i></sub> versus NH<sub>3</sub>
control and demonstrates the relevance of pH as an air quality parameter. We
find that, regardless of the locations examined, it is only when ambient
particle pH drops below an approximate critical value of 3 (slightly higher
in warm and slightly lower in cold seasons) that NH<sub>3</sub> reduction
leads to an effective response in PM<sub>2.5</sub> mass. The required amount of
NH<sub>3</sub> reduction to reach the critical pH and efficiently decrease
NH<sub>4</sub>NO<sub>3</sub> at different sites is assessed. Owing to the linkage
between NH<sub>3</sub> emissions and agricultural productivity, the substantial
NH<sub>3</sub> reduction required in some locations may not be feasible.
Finally, controlling NH<sub>3</sub> emissions to increase aerosol acidity and
evaporate NH<sub>4</sub>NO<sub>3</sub> will have other effects, beyond reduction of
PM<sub>2.5</sub> NH<sub>4</sub>NO<sub>3</sub>, such as increasing aerosol toxicity and
potentially altering the deposition patterns of nitrogen and trace nutrients.</p> |
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ISSN: | 1680-7316 1680-7324 |