Heterogeneous formation of particulate nitrate under ammonium-rich regimes during the high-PM<sub>2.5</sub> events in Nanjing, China
oleh: Y.-C. Lin, Y.-C. Lin, Y.-C. Lin, Y.-L. Zhang, Y.-L. Zhang, Y.-L. Zhang, M.-Y. Fan, M.-Y. Fan, M. Bao, M. Bao
| Format: | Article |
|---|---|
| Diterbitkan: | Copernicus Publications 2020-04-01 |
Deskripsi
<p>Particulate nitrate (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M2" 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="4c315b3ea451cf26923ad12993612b33"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-20-3999-2020-ie00001.svg" width="25pt" height="16pt" src="acp-20-3999-2020-ie00001.png"/></svg:svg></span></span>) not only influences regional climates but also contributes to the acidification of terrestrial and aquatic ecosystems. In 2016 and 2017, four intensive online measurements of water-soluble ions in PM<span class="inline-formula"><sub>2.5</sub></span> were conducted in Nanjing City in order to investigate the potential formation mechanisms of particulate nitrate. During the sampling periods, <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M4" 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="e16cba38499a6a16cb1a10e488ec56da"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-20-3999-2020-ie00002.svg" width="25pt" height="16pt" src="acp-20-3999-2020-ie00002.png"/></svg:svg></span></span> was the predominant species, accounting approximately for 35 % of the total water-soluble inorganic ions, followed by <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M5" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">SO</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="29pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="28cd4f8c12cf9ef751545712573a522a"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-20-3999-2020-ie00003.svg" width="29pt" height="17pt" src="acp-20-3999-2020-ie00003.png"/></svg:svg></span></span> (33 %) and <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M6" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NH</mi><mn mathvariant="normal">4</mn><mo>+</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="6ca56caa63735c5009fe6b299c1a126b"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-20-3999-2020-ie00004.svg" width="24pt" height="15pt" src="acp-20-3999-2020-ie00004.png"/></svg:svg></span></span> (24 %). Significant enhancements of nitrate aerosols in terms of both absolute concentrations and relative abundances suggested that <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M7" 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="a02883d0956e7dc256b9fe9fffa70b09"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-20-3999-2020-ie00005.svg" width="25pt" height="16pt" src="acp-20-3999-2020-ie00005.png"/></svg:svg></span></span> was a major contributing species to high-PM<span class="inline-formula"><sub>2.5</sub></span> events (hourly PM<span class="inline-formula"><sub>2.5</sub>≥150</span> <span class="inline-formula">µ</span>g m<span class="inline-formula"><sup>−3</sup></span>). High <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M12" 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="737339a8d3517116341490f01d8cfecf"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-20-3999-2020-ie00006.svg" width="25pt" height="16pt" src="acp-20-3999-2020-ie00006.png"/></svg:svg></span></span> concentrations mainly occurred under <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">NH</mi><mn mathvariant="normal">4</mn><mo>+</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="9d8f7ee8bf88d657d75cdcf077dbe3e2"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-20-3999-2020-ie00007.svg" width="24pt" height="15pt" src="acp-20-3999-2020-ie00007.png"/></svg:svg></span></span>-rich conditions, implying that the formation of nitrate aerosols in Nanjing involved <span class="inline-formula">NH<sub>3</sub></span>. During the high-PM<span class="inline-formula"><sub>2.5</sub></span> events, the nitrogen conversion ratios (<span class="inline-formula"><i>F</i><sub>n</sub></span>) were positively correlated with the aerosol liquid water content (ALWC; <span class="inline-formula"><i>R</i>>0.72</span> and <span class="inline-formula"><i>p</i><0.05</span>). Meanwhile, increasing <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M19" 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="7248c728767abac31fc80ac33e5f4469"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-20-3999-2020-ie00008.svg" width="25pt" height="16pt" src="acp-20-3999-2020-ie00008.png"/></svg:svg></span></span> concentrations regularly coincided with increasing ALWC and decreasing <span class="inline-formula">O<sub><i>x</i></sub></span> (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M21" display="inline" overflow="scroll" dspmath="mathml"><mrow><mrow class="chem"><msub><mi mathvariant="normal">O</mi><mi>x</mi></msub></mrow><mo>=</mo><mrow class="chem"><msub><mi mathvariant="normal">O</mi><mn mathvariant="normal">3</mn></msub></mrow><mo>+</mo><mrow class="chem"><msub><mi mathvariant="normal">NO</mi><mn mathvariant="normal">2</mn></msub></mrow></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="74pt" height="13pt" class="svg-formula" dspmath="mathimg" md5hash="7aa02352661b2ab474ee3937394cf483"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-20-3999-2020-ie00009.svg" width="74pt" height="13pt" src="acp-20-3999-2020-ie00009.png"/></svg:svg></span></span>). These results suggested that the heterogeneous reaction was probably a major mechanism of nitrate formation during the high-PM<span class="inline-formula"><sub>2.5</sub></span> events. Moreover, the average production rate of <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M23" 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="9d4fcb6817fb360ca45e4c6c5f1d67f7"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-20-3999-2020-ie00010.svg" width="25pt" height="16pt" src="acp-20-3999-2020-ie00010.png"/></svg:svg></span></span> by heterogeneous processes was estimated to be 12.6 % h<span class="inline-formula"><sup>−1</sup></span> (4.1 <span class="inline-formula">µ</span>g m<span class="inline-formula"><sup>−3</sup></span> h<span class="inline-formula"><sup>−1</sup></span>), which was much higher than that (2.5 % h<span class="inline-formula"><sup>−1</sup></span>; 0.8 <span class="inline-formula">µ</span>g m<span class="inline-formula"><sup>−3</sup></span> h<span class="inline-formula"><sup>−1</sup></span>) of gas-phase reactions. This can also explain the abrupt increases in nitrate concentrations during the high-PM<span class="inline-formula"><sub>2.5</sub></span> events. Utilizing the ISORROPIA II model, we found that nitrate aerosol formation in Nanjing during the high-PM<span class="inline-formula"><sub>2.5</sub></span> events was <span class="inline-formula">HNO<sub>3</sub></span> limited. This indicated that control of <span class="inline-formula">NO<sub><i>x</i></sub></span> emissions will be able to efficiently reduce airborne particulate nitrate concentrations and improve the air quality in this industrial city.</p>