Air quality deterioration episode associated with a typhoon over the complex topographic environment in central Taiwan
<p>Air pollution is typically at its lowest in Taiwan during summer. The mean concentrations of PM<span class="inline-formula"><sub>10</sub></span>, PM<span class="inline-formula"><sub>2.5</sub></span>, and daytime ozone (08:0...
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| Autores principales: | , , , , , |
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| Formato: | article |
| Lenguaje: | EN |
| Publicado: |
Copernicus Publications
2021
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| Materias: | |
| Acceso en línea: | https://doaj.org/article/26b636895af94d7a9c8a6dd204cee1af |
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| Sumario: | <p>Air pollution is typically at its lowest in Taiwan during summer. The mean
concentrations of PM<span class="inline-formula"><sub>10</sub></span>, PM<span class="inline-formula"><sub>2.5</sub></span>, and daytime ozone (08:00–17:00 LST) during summer (June–August) over central Taiwan were 35–40 <span class="inline-formula">µ</span>g m<span class="inline-formula"><sup>−3</sup></span>, 18–22 <span class="inline-formula">µ</span>g m<span class="inline-formula"><sup>−3</sup></span>, and 30–42 ppb, respectively, between
2004 and 2019. Sampling analysis revealed that the contribution of organic
carbon (OC) to PM<span class="inline-formula"><sub>2.5</sub></span> could have exceeded 30 % in urban and inland mountain
sites during July in 2017 and 2018. Frequent episodes of air quality
deterioration occur over the western plains of Taiwan when an easterly
typhoon circulation interacts with the complex topographic structure of the
island. We explored an episode of air quality deterioration that was
associated with a typhoon between 15 and 17 July 2018 using the Weather
Research Forecasting with Chemistry (WRF-Chem) model. The results indicated
that the continual formation of low-pressure systems or typhoons in the area
between Taiwan and Luzon island in the Philippines provided a strong
easterly ambient flow, which lasted for an extended period between 15 and 17
July. The interaction between the easterly flow and Taiwan's Central
Mountain Range (CMR) resulted in stable weather conditions and weak wind
speed in western Taiwan during the study period. Numerical modeling also
indicated that a lee side vortex easily formed, and the wind direction
could have changed from southwesterly to northwesterly over central Taiwan
because of the interaction between the typhoon circulation and the CMR. The
northwesterly wind coupled with a sea breeze was conducive to the transport
of air pollutants from the coastal upstream industrial and urban areas to
the inland area. The dynamic process for the wind direction changed given a
reasonable explanation for why the observed SO<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M8" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">4</mn><mrow><mn mathvariant="normal">2</mn><mo>-</mo></mrow></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="13pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="310c409436de724d2b31553f6031e416"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-21-16893-2021-ie00001.svg" width="13pt" height="17pt" src="acp-21-16893-2021-ie00001.png"/></svg:svg></span></span> became the major
contributor to PM<span class="inline-formula"><sub>2.5</sub></span> during the episode. SO<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M10" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">4</mn><mrow><mn mathvariant="normal">2</mn><mo>-</mo></mrow></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="13pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="6051c44ba131ac206db43e824688e92d"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-21-16893-2021-ie00002.svg" width="13pt" height="17pt" src="acp-21-16893-2021-ie00002.png"/></svg:svg></span></span> contribution
proportions (%) to PM<span class="inline-formula"><sub>2.5</sub></span> at the coastal, urban, and mountain sites
were 9.4 <span class="inline-formula">µ</span>g m<span class="inline-formula"><sup>−3</sup></span> (30.5 %), 12.1 <span class="inline-formula">µ</span>g m<span class="inline-formula"><sup>−3</sup></span> (29.9 %),
and 11.6 <span class="inline-formula">µ</span>g m<span class="inline-formula"><sup>−3</sup></span> (29.7 %), respectively. Moreover, the
variation of the boundary layer height had a strong effect on the
concentration level of both PM<span class="inline-formula"><sub>2.5</sub></span> and ozone. The lee
vortex and land–sea breeze, as well as the boundary layer development, were
the key mechanisms in air pollutant accumulation and transport. As typhoons
frequently occur around Taiwan during summer and fall, their effect on
the island's air quality merits further research attention.</p> |
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