Measurement and model analyses of the ozone variation during 2006 to 2015 and its response to emission change in megacity Shanghai, China
<p><span id="page9018"/>The fine particles (PM<span class="inline-formula"><sub>2.5</sub></span>) in China have decreased significantly in recent years as a result of the implementation of Chinese Clean Air Action Plan since 2013, while the <...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-07-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/19/9017/2019/acp-19-9017-2019.pdf |
| Summary: | <p><span id="page9018"/>The fine particles (PM<span class="inline-formula"><sub>2.5</sub></span>) in China have decreased significantly in
recent years as a result of the implementation of Chinese Clean Air Action Plan
since 2013, while the <span class="inline-formula">O<sub>3</sub></span> pollution is getting worse, especially in
megacities such as Beijing and Shanghai. Better understanding of the elevated
<span class="inline-formula">O<sub>3</sub></span> pollution in Chinese megacities and its response to emission change
is important for developing an effective emission control strategy in
the future. In this study, we analyze the significant increasing trend of daily
maximum <span class="inline-formula">O<sub>3</sub></span> concentration from 2006 to 2015 in the megacity Shanghai
with the variability of 0.8–1.3 ppbv yr<span class="inline-formula"><sup>−1</sup></span>. It could likely be attributed to
the notable reduction in <span class="inline-formula">NO<sub><i>x</i></sub></span> concentrations with the decreasing rate of
1.86–2.15 ppbv yr<span class="inline-formula"><sup>−1</sup></span> accompanied by the small change in VOCs during
the same period by excluding the weak trends of meteorological impacts on
local dispersion (wind speed), regional transport (wind direction), and
<span class="inline-formula">O<sub>3</sub></span> photolysis (solar radiation). It is further illustrated by using a
state-of-the-art regional chemical and dynamical model (WRF-Chem) to explore the
<span class="inline-formula">O<sub>3</sub></span> variation response to the reduction in <span class="inline-formula">NO<sub><i>x</i></sub></span> emissions in
Shanghai. The control experiment conducted for September of 2009 shows
excellent performance for <span class="inline-formula">O<sub>3</sub></span> and <span class="inline-formula">NO<sub><i>x</i></sub></span> simulations, including both
the spatial distribution pattern and the day-by-day variation through
comparison with six in situ measurements from the MIRAGE-Shanghai field campaign.
Sensitivity experiments with 30 % reduction in <span class="inline-formula">NO<sub><i>x</i></sub></span> emissions from 2009
to 2015 in Shanghai estimated by Shanghai Environmental Monitoring Center
shows that the calculated <span class="inline-formula">O<sub>3</sub></span> concentrations exhibit obvious enhancement
by 4–7 ppbv in urban zones with increasing variability of 0.96–1.06 ppbv yr<span class="inline-formula"><sup>−1</sup></span>, which is consistent with the observed <span class="inline-formula">O<sub>3</sub></span> trend as a
result of the strong VOC-limited condition for <span class="inline-formula">O<sub>3</sub></span> production. The large
reduction in <span class="inline-formula">NO<sub><i>x</i></sub></span> combined with less change in VOCs in the past 10
years promotes the <span class="inline-formula">O<sub>3</sub></span> production in Shanghai to move towards
an <span class="inline-formula">NO<sub><i>x</i></sub></span>-limited regime. Further analysis of the WRF-Chem experiments and
<span class="inline-formula">O<sub>3</sub></span> isopleth diagram suggests that the <span class="inline-formula">O<sub>3</sub></span> production downtown
is still under a VOC-limited regime after 2015 despite the remarkable
<span class="inline-formula">NO<sub><i>x</i></sub></span> reduction, while it moves to the transition regime between
<span class="inline-formula">NO<sub><i>x</i></sub></span>-limited and VOC-limited in sub-urban zones. Supposing the
insignificant VOC variation persists, the <span class="inline-formula">O<sub>3</sub></span> concentration downtown
would keep increasing until 2020 with the further 20 % reduction in
<span class="inline-formula">NO<sub><i>x</i></sub></span> emission after 2015 estimated by Shanghai Clean Air Action Plan.
The <span class="inline-formula">O<sub>3</sub></span> production in Shanghai will switch from a VOC-limited to
an <span class="inline-formula">NO<sub><i>x</i></sub></span>-limited regime after 2020 except for downtown area, which is likely
close to the transition regime. As a result the <span class="inline-formula">O<sub>3</sub></span> concentration will
decrease by 2–3 ppbv in sub-urban zones and by more than 4 ppbv in rural areas as a response to a 20 % reduction in <span class="inline-formula">NO<sub><i>x</i></sub></span> emission after 2020, whereas it is not
sensitive to both <span class="inline-formula">NO<sub><i>x</i></sub></span> and VOC changes downtown. This result reveals
that the control strategy of <span class="inline-formula">O<sub>3</sub></span> pollution is a very complex process
and needs to be carefully studied.</p> |
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| ISSN: | 1680-7316 1680-7324 |