Nonlinear responses of particulate nitrate to NO<sub>x</sub> emission controls in the megalopolises of China
<p>Nitrate is an increasingly important component of fine particulate matter (<span class="inline-formula">PM<sub>2.5</sub></span>) in Chinese cities. The production of nitrate is not only related to the abundance of its precursor, but it is also supported by...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2021-10-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/21/15135/2021/acp-21-15135-2021.pdf |
| Summary: | <p>Nitrate is an increasingly important component of fine particulate matter (<span class="inline-formula">PM<sub>2.5</sub></span>) in Chinese cities. The production of nitrate is not only
related to the abundance of its precursor, but it is also supported by the atmospheric photochemical oxidants, raising a new challenge for the current
emission control actions in China. This paper uses comprehensive measurements and a regional meteorology–chemistry model with optimized mechanisms
to establish the nonlinear responses between particulate nitrate and the emission controls of nitrogen oxides (<span class="inline-formula">NO<sub><i>x</i></sub></span>) in the megalopolises
of China. Nitrate is an essential component of <span class="inline-formula">PM<sub>2.5</sub></span> in eastern China, accounting for 9.4 %–15.5 % and 11.5 %–32.1 % of
the <span class="inline-formula">PM<sub>2.5</sub></span> mass for the warm and cold seasons. The hypothetical <span class="inline-formula">NO<sub><i>x</i></sub></span> emission reduction scenarios
(<span class="inline-formula">−</span>10 % to <span class="inline-formula">−</span>80 %) during summer–autumn result in almost linearly lower <span class="inline-formula">PM<sub>2.5</sub></span> by <span class="inline-formula">−</span>2.2 % in Beijing–Tianjin–Hebei
(BTH) and <span class="inline-formula">−</span>2.9 % in Yangtze River Delta (YRD) per 10 % reduction of <span class="inline-formula">NO<sub><i>x</i></sub></span> emissions, whereas they lead to a rather complicated
response of PM components in winter. Wintertime nitrate is found to increase by <span class="inline-formula">+</span>4.1 % in BTH and <span class="inline-formula">+</span>5.1 % in YRD per 10 % reduction of
<span class="inline-formula">NO<sub><i>x</i></sub></span> emissions, with nearly unchanged nitric acid (<span class="inline-formula">HNO<sub>3</sub></span>) and higher dinitrogen pentoxide (N<span class="inline-formula"><sub>2</sub></span>O<span class="inline-formula"><sub>5</sub></span>) intermediate
products produced from the increased atmospheric oxidant levels. An inflexion point appears at 30 %–50 % <span class="inline-formula">NO<sub><i>x</i></sub></span> emission
reduction, and a further reduction in <span class="inline-formula">NO<sub><i>x</i></sub></span> emissions is predicted to cause <span class="inline-formula">−</span>10.5 % reduction of nitrate for BTH and <span class="inline-formula">−</span>7.7 %
for YRD per 10 % reduction of <span class="inline-formula">NO<sub><i>x</i></sub></span> emissions. In addition, the 2012–2016 <span class="inline-formula">NO<sub><i>x</i></sub></span> control strategy actually leads to
no changes or even increases of nitrate in some areas (8.8 % in BTH and 14.4 % in YRD) during winter. Our results also emphasize that
ammonia (<span class="inline-formula">NH<sub>3</sub></span>) and volatile organic compounds (VOCs) are effective in controlling nitrate pollution, whereas decreasing the
sulfur dioxide (<span class="inline-formula">SO<sub>2</sub></span>) and <span class="inline-formula">NO<sub><i>x</i></sub></span> emissions may have counterintuitive effects on nitrate aerosols. This paper helps
understand the nonlinear aerosol and photochemistry feedbacks and defines the effectiveness of proposed mitigations for the increasingly serious
nitrate pollution in China.</p> |
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| ISSN: | 1680-7316 1680-7324 |