Measurement report: Effects of photochemical aging on the formation and evolution of summertime secondary aerosol in Beijing
oleh: T. Chen, J. Liu, J. Liu, Q. Ma, Q. Ma, Q. Ma, B. Chu, B. Chu, B. Chu, P. Zhang, J. Ma, J. Ma, J. Ma, Y. Liu, C. Zhong, C. Zhong, P. Liu, Y. Wang, Y. Mu, Y. Mu, Y. Mu, H. He, H. He, H. He
| Format: | Article |
|---|---|
| Diterbitkan: | Copernicus Publications 2021-02-01 |
Deskripsi
<p>Atmospheric submicrometer aerosols have a great effect on air quality and human health, while their formation and evolution processes are still not fully understood. Herein, the crucial role of atmospheric oxidation capacity, as characterized by OH exposure dose in the formation and evolution of secondary submicrometer aerosols, was systematically investigated based on a highly time-resolved chemical characterization of <span class="inline-formula">PM<sub>1</sub></span> in a southern suburb of Beijing in summertime from 25 July to 21 August 2019. The averaged concentration of <span class="inline-formula">PM<sub>1</sub></span> was 19.3 <span class="inline-formula">±</span> 11.3 <span class="inline-formula">µg m<sup>−3</sup></span>, and nearly half (48.3 %) of the mass was organic aerosols (OAs) during the observation period. The equivalent photochemical age (<span class="inline-formula"><i>t</i><sub>a</sub></span>) estimated from the ratios of toluene to benzene was applied to characterize the OH exposure dose of the air mass, in which an observation period with the similar sources and minimal influence of fresh emission was adopted. The relationships of non-refractory <span class="inline-formula">PM<sub>1</sub></span> species, OA factors (i.e., one hydrocarbon-like and three oxygenated organic aerosol factors) and elemental compositions (e.g., <span class="inline-formula">H∕C</span>, <span class="inline-formula">O∕C</span>, <span class="inline-formula">N∕C</span>, <span class="inline-formula">S∕C</span>, <span class="inline-formula">OM∕OC</span>, and <span class="inline-formula">OSc</span>) to <span class="inline-formula"><i>t</i><sub>a</sub></span> were analyzed in detail. It was found that higher <span class="inline-formula">PM<sub>1</sub></span> concentration accompanied longer <span class="inline-formula"><i>t</i><sub>a</sub></span>, with an average increase rate of 0.8 <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M16" display="inline" overflow="scroll" dspmath="mathml"><mrow class="unit"><mi mathvariant="normal">µ</mi><mi mathvariant="normal">g</mi><mspace linebreak="nobreak" width="0.125em"/><msup><mi mathvariant="normal">m</mi><mrow><mo>-</mo><mn mathvariant="normal">3</mn></mrow></msup><mspace width="0.125em" linebreak="nobreak"/><msup><mi mathvariant="normal">h</mi><mrow><mo>-</mo><mn mathvariant="normal">1</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="53pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="6a3cc89f647152ab0ac1cbe0619e6fd1"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-21-1341-2021-ie00001.svg" width="53pt" height="15pt" src="acp-21-1341-2021-ie00001.png"/></svg:svg></span></span>. Meanwhile, the formation of sulfate and more oxidized oxygenated OA were most sensitive to the increase in <span class="inline-formula"><i>t</i><sub>a</sub></span>, and their contributions to <span class="inline-formula">PM<sub>1</sub></span> were enhanced from 22 % to 28 % and from 29 % to 48 %, respectively, as <span class="inline-formula"><i>t</i><sub>a</sub></span> increased. In addition, OSc and the ratios of <span class="inline-formula">O∕C</span> and <span class="inline-formula">OM∕OC</span> increased with the increase in <span class="inline-formula"><i>t</i><sub>a</sub></span>. These results indicated that photochemical aging is a key factor leading to the evolution of OA and the increase in <span class="inline-formula">PM<sub>1</sub></span> in summertime.</p>