Nitrate formation from heterogeneous uptake of dinitrogen pentoxide during a severe winter haze in southern China
<p>Nitrate (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M1" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant=&qu...
| 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/18/17515/2018/acp-18-17515-2018.pdf |
| Summary: | <p>Nitrate (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M1" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NO</mi><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="57a4663cbf0d11bf294d99bb32c9ae29"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-18-17515-2018-ie00001.svg" width="25pt" height="16pt" src="acp-18-17515-2018-ie00001.png"/></svg:svg></span></span>) has become a major component of fine particulate matter
(PM<span class="inline-formula"><sub>2.5</sub></span>) during hazy days in China. However, the role of the
heterogeneous reactions of dinitrogen pentoxide (<span class="inline-formula">N<sub>2</sub>O<sub>5</sub></span>) in
nitrate formation is not well constrained. In January 2017, a severe haze
event occurred in the Pearl River Delta (PRD) of southern China during which
high levels of PM<span class="inline-formula"><sub>2.5</sub></span> (<span class="inline-formula">∼400</span> <span class="inline-formula">µ</span>g m<span class="inline-formula"><sup>−3</sup></span>) and
<span class="inline-formula">O<sub>3</sub></span> (<span class="inline-formula">∼160</span> ppbv) were observed at a semi-rural site (Heshan)
in the western PRD. Nitrate concentrations reached 108 <span class="inline-formula">µ</span>g m<span class="inline-formula"><sup>−3</sup></span>
(1 h time resolution), and the contribution of nitrate to PM<span class="inline-formula"><sub>2.5</sub></span> was
nearly 40 %. Concurrent increases in <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M13" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NO</mi><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="9712381780fcc4de6c4d72f703a8771c"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-18-17515-2018-ie00002.svg" width="25pt" height="16pt" src="acp-18-17515-2018-ie00002.png"/></svg:svg></span></span> and
<span class="inline-formula">ClNO<sub>2</sub></span> (with a maximum value of 8.3 ppbv at a 1 min time
resolution) were observed in the first several hours after sunset, indicating
an intense <span class="inline-formula">N<sub>2</sub>O<sub>5</sub></span> heterogeneous uptake by aerosols.
The formation potential of <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M16" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NO</mi><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="48a6d5724cc017ced9c974ab9a81c03a"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-18-17515-2018-ie00003.svg" width="25pt" height="16pt" src="acp-18-17515-2018-ie00003.png"/></svg:svg></span></span> via <span class="inline-formula">N<sub>2</sub>O<sub>5</sub></span> heterogeneous reactions was
estimated to be between 29.0 and 77.3 <span class="inline-formula">µ</span>g m<span class="inline-formula"><sup>−3</sup></span> in the early
hours (2 to 6 h) after sunset based on the measurement data, which could
completely explain the measured increase in the <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M20" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NO</mi><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="827b0fe0e97f70953101fc9e20cd0031"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-18-17515-2018-ie00004.svg" width="25pt" height="16pt" src="acp-18-17515-2018-ie00004.png"/></svg:svg></span></span>
concentration during the same time period. Daytime production of nitric acid
from the gas-phase reaction of <span class="inline-formula">OH+NO<sub>2</sub></span> was calculated
with a chemical box model built using the Master Chemical Mechanism
(MCM v3.3.1) and constrained by the measurement data. The integrated
nocturnal nitrate formed via <span class="inline-formula">N<sub>2</sub>O<sub>5</sub></span> chemistry was comparable to or
even higher than the nitric acid formed during the day. This study confirms
that <span class="inline-formula">N<sub>2</sub>O<sub>5</sub></span> heterogeneous chemistry was a significant source of
aerosol nitrate during hazy days in southern China.</p> |
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| ISSN: | 1680-7316 1680-7324 |