Understanding summertime peroxyacetyl nitrate (PAN) formation and its relation to aerosol pollution: insights from high-resolution measurements and modeling
<p>Peroxyacetyl nitrate (PAN), a key indicator of photochemical pollution, is generated similarly to ozone (O<span class="inline-formula"><sub>3</sub></span>), through reactions involving specific volatile organic compounds (VOCs) and nitrogen oxides. Notably,...
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| Main Authors: | , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2025-01-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/25/905/2025/acp-25-905-2025.pdf |
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| Summary: | <p>Peroxyacetyl nitrate (PAN), a key indicator of photochemical pollution, is generated similarly to ozone (O<span class="inline-formula"><sub>3</sub></span>), through reactions involving specific volatile organic compounds (VOCs) and nitrogen oxides. Notably, PAN has been observed at unexpectedly high concentrations (maximum: 3.04 ppb) during the summertime. The average daily values of PAN show a strong correlation with black carbon (BC) (<span class="inline-formula"><i>R</i></span> <span class="inline-formula">=</span> 0.77) and O<span class="inline-formula"><sub>3</sub></span> (<span class="inline-formula"><i>R</i></span> <span class="inline-formula">=</span> 0.77), suggesting a close connection between summertime haze and photochemical pollution. We addressed the puzzle of summertime PAN formation and its association with aerosol pollution under high-O<span class="inline-formula"><sub>3</sub></span> conditions in Xiamen, a coastal city in southeastern China, by analyzing continuous high-temporal-resolution data utilizing box modeling in conjunction with the Master Chemical Mechanism (MCM) model. The MCM model, with an index of agreement (IOA) value of 0.75, effectively investigates PAN formation, performing better during the clean period (<span class="inline-formula"><i>R</i><sup>2</sup></span>: 0.68; slope <span class="inline-formula"><i>K</i></span>: 0.91) than the haze one (<span class="inline-formula"><i>R</i><sup>2</sup></span>: 0.47; slope <span class="inline-formula"><i>K</i></span>: 0.75). Using eXtreme Gradient Boosting (XGBoost), we identified NH<span class="inline-formula"><sub>3</sub></span>, NO<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M13" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="9pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="a192f22c747584054322d55d69a940ca"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-25-905-2025-ie00001.svg" width="9pt" height="16pt" src="acp-25-905-2025-ie00001.png"/></svg:svg></span></span>, and PM<span class="inline-formula"><sub>2.5</sub></span> as the primary factors for simulation bias. Moreover, the net production rate of PAN becomes negative with PAN constrained, suggesting an unknown compensatory mechanism. Both relative incremental reactivity (RIR) and empirical kinetic modeling approach (EKMA) analyses indicate that PAN formation is VOC-controlled. Controlling emissions of VOCs, particularly alkenes, C<span class="inline-formula"><sub>5</sub></span>H<span class="inline-formula"><sub>8</sub></span>, and aromatics, would mitigate PAN pollution. PAN promotes OH and HO<span class="inline-formula"><sub>2</sub></span> while inhibiting the formation of O<span class="inline-formula"><sub>3</sub></span>, RO<span class="inline-formula"><sub>2</sub></span>, NO, and NO<span class="inline-formula"><sub>2</sub></span>. This study deepens our comprehension of PAN photochemistry while also offering scientific insights for guiding future PAN pollution control strategies.</p> |
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| ISSN: | 1680-7316 1680-7324 |