Rapid SO<sub>2</sub> emission reductions significantly increase tropospheric ammonia concentrations over the North China Plain
<p>The North China Plain has been identified as a significant hotspot of ammonia (<span class="inline-formula">NH<sub>3</sub></span>) due to extensive agricultural activities. Satellite observations suggest a significant increase of about 30 % in tr...
| Main Authors: | , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-12-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/18/17933/2018/acp-18-17933-2018.pdf |
| Summary: | <p>The North China Plain has been identified as a significant hotspot of ammonia
(<span class="inline-formula">NH<sub>3</sub></span>) due to extensive agricultural activities. Satellite
observations suggest a significant increase of about 30 % in tropospheric
gas-phase <span class="inline-formula">NH<sub>3</sub></span> concentrations in this area during 2008–2016.
However, the estimated <span class="inline-formula">NH<sub>3</sub></span> emissions decreased slightly by 7 %
because of changes in Chinese agricultural practices, i.e., the transition in
fertilizer types from ammonium carbonate fertilizer to urea, and in the
livestock rearing system from free-range to intensive farming. We note that
the emissions of sulfur dioxide (<span class="inline-formula">SO<sub>2</sub></span>) have rapidly declined by
about 60 % over the recent few years. By integrating measurements from
ground and satellite, a long-term anthropogenic <span class="inline-formula">NH<sub>3</sub></span> emission
inventory, and chemical transport model simulations, we find that this large
<span class="inline-formula">SO<sub>2</sub></span> emission reduction is responsible for the <span class="inline-formula">NH<sub>3</sub></span>
increase over the North China Plain. The simulations for the period
2008–2016 demonstrate that the annual average sulfate concentrations
decreased by about 50 %, which significantly weakens the formation of
ammonium sulfate and increases the average proportions of gas-phase
<span class="inline-formula">NH<sub>3</sub></span> within the total <span class="inline-formula">NH<sub>3</sub></span> column concentrations from
26 % (2008) to 37 % (2016). By fixing <span class="inline-formula">SO<sub>2</sub></span> emissions of 2008
in those multi-year simulations, the increasing trend of the tropospheric
<span class="inline-formula">NH<sub>3</sub></span> concentrations is not observed. Both the decreases in sulfate
and increases in <span class="inline-formula">NH<sub>3</sub></span> concentrations show highest values in summer,
possibly because the formation of sulfate aerosols is more sensitive to
<span class="inline-formula">SO<sub>2</sub></span> emission reductions in summer than in other seasons. Besides,
the changes in <span class="inline-formula">NO<sub><i>x</i></sub></span> emissions and meteorological conditions
both decreased the <span class="inline-formula">NH<sub>3</sub></span> column concentrations by about 3 % in
the study period. Our simulations suggest that the moderate reduction in
<span class="inline-formula">NO<sub><i>x</i></sub></span> emissions (16 %) favors the formation of
particulate nitrate by elevating ozone concentrations in the lower
troposphere.</p> |
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| ISSN: | 1680-7316 1680-7324 |