Intercomparison of O<sub>3</sub> formation and radical chemistry in the past decade at a suburban site in Hong Kong
<p>Hong Kong, as one of the densely populated metropolises in East Asia, has been suffering from severe photochemical smog in the past decades, though the observed nitrogen oxides (<span class="inline-formula">NO<sub><i>x</i></sub></span>) and tota...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-04-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/19/5127/2019/acp-19-5127-2019.pdf |
| Summary: | <p>Hong Kong, as one of the densely populated metropolises in East Asia, has
been suffering from severe photochemical smog in the past decades, though
the observed nitrogen oxides (<span class="inline-formula">NO<sub><i>x</i></sub></span>) and total volatile organic compounds (TVOCs) were significantly reduced. This study, based on the observation
data in the autumns of 2007, 2013 and 2016, investigated the photochemical
ozone (<span class="inline-formula">O<sub>3</sub></span>) formation and radical chemistry during the three sampling
periods in Hong Kong with the aid of a photochemical box model incorporating
the Master Chemical Mechanism (PBM–MCM). While the simulated locally
produced <span class="inline-formula">O<sub>3</sub></span> remained unchanged (<span class="inline-formula"><i>p</i>=0.73</span>) from 2007 to 2013, the
observed <span class="inline-formula">O<sub>3</sub></span> increased (<span class="inline-formula"><i>p</i></span> < 0.05) at a rate of 1.78 ppbv yr<span class="inline-formula"><sup>−1</sup></span> driven
by the rise in regionally transported <span class="inline-formula">O<sub>3</sub></span> (<span class="inline-formula">1.77±0.04</span> ppbv yr<span class="inline-formula"><sup>−1</sup></span>).
Both the observed and locally produced <span class="inline-formula">O<sub>3</sub></span> decreased (<span class="inline-formula"><i>p</i></span> < 0.05)
from the VOC sampling days in 2013 to those in 2016 at a rate of
<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M15" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><mn mathvariant="normal">5.31</mn><mo>±</mo><mn mathvariant="normal">0.07</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="64pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="be1cf5c749380f276f71556d80fa0a42"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-5127-2019-ie00001.svg" width="64pt" height="10pt" src="acp-19-5127-2019-ie00001.png"/></svg:svg></span></span> and <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M16" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><mn mathvariant="normal">5.52</mn><mo>±</mo><mn mathvariant="normal">0.05</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="64pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="d9ecafceebb0d9f155c7326480785931"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-5127-2019-ie00002.svg" width="64pt" height="10pt" src="acp-19-5127-2019-ie00002.png"/></svg:svg></span></span> ppbv yr<span class="inline-formula"><sup>−1</sup></span>, respectively.
However, a leveling-off (<span class="inline-formula"><i>p</i>=0.32</span>) was simulated for the regionally
transported <span class="inline-formula">O<sub>3</sub></span> during 2013–2016. The mitigation of autumn <span class="inline-formula">O<sub>3</sub></span>
pollution in this region was further confirmed by the continuous monitoring
data, which have never been reported. Benefiting from the
air pollution control measures taken in Hong Kong, the local <span class="inline-formula">O<sub>3</sub></span>
production rate decreased remarkably (<span class="inline-formula"><i>p</i></span> < 0.05) from 2007 to 2016,
along with the lowering of the recycling rate of the hydroxyl radical (OH).
Specifically, VOCs emitted from the source of liquefied petroleum gas (LPG)
usage and gasoline evaporation decreased in this decade at a rate of
<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M23" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><mn mathvariant="normal">2.61</mn><mo>±</mo><mn mathvariant="normal">0.03</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="64pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="0ebe34521245f2445470ebf9df28fa48"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-5127-2019-ie00003.svg" width="64pt" height="10pt" src="acp-19-5127-2019-ie00003.png"/></svg:svg></span></span> ppbv yr<span class="inline-formula"><sup>−1</sup></span>, leading to a reduction of the <span class="inline-formula">O<sub>3</sub></span>
production rate from <span class="inline-formula">0.51±0.11</span> ppbv h<span class="inline-formula"><sup>−1</sup></span> in 2007 to <span class="inline-formula">0.10±0.02</span> ppbv h<span class="inline-formula"><sup>−1</sup></span> in 2016. In addition, solvent usage made decreasing
contributions to both VOCs (rate <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M30" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>=</mo><mo>-</mo><mn mathvariant="normal">2.29</mn><mo>±</mo><mn mathvariant="normal">0.03</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="74pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="7fc652daa6f8ff67bd78270c8ae0f1c2"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-5127-2019-ie00004.svg" width="74pt" height="10pt" src="acp-19-5127-2019-ie00004.png"/></svg:svg></span></span> ppbv yr<span class="inline-formula"><sup>−1</sup></span>) and
local <span class="inline-formula">O<sub>3</sub></span> production rate (<span class="inline-formula">1.22±0.17</span> and <span class="inline-formula">0.14±0.05</span> ppbv h<span class="inline-formula"><sup>−1</sup></span> in 2007 and 2016, respectively) in the same period. All the rates
reported here were for the VOC sampling days in the three sampling
campaigns. It is noteworthy that meteorological changes also play important
roles in the inter-annual variations in the observed <span class="inline-formula">O<sub>3</sub></span> and the
simulated <span class="inline-formula">O<sub>3</sub></span> production rates. Evaluations with more data in longer
periods are therefore recommended. The analyses on the decadal changes of
the local and regional photochemistry in Hong Kong in this study may be a
reference for combating China's nationwide <span class="inline-formula">O<sub>3</sub></span> pollution in near
future.</p> |
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| ISSN: | 1680-7316 1680-7324 |