Molecular analysis of secondary organic aerosol and brown carbon from the oxidation of indole
<p>Indole (ind) is a nitrogen-containing heterocyclic volatile organic compound commonly emitted from animal husbandry and from different plants like maize with global emissions of 0.1 Tg yr<span class="inline-formula"><sup>−1</sup></span>. The chemical compos...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2024-02-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/24/2639/2024/acp-24-2639-2024.pdf |
| Summary: | <p>Indole (ind) is a nitrogen-containing heterocyclic volatile organic compound commonly emitted from animal husbandry and from different plants like maize with global emissions of 0.1 Tg yr<span class="inline-formula"><sup>−1</sup></span>. The chemical composition and optical properties of indole secondary organic aerosol (SOA) and brown carbon (BrC) are still not well understood. To address this, environmental chamber experiments were conducted to investigate the oxidation of indole at atmospherically relevant concentrations of selected oxidants (OH radicals and O<span class="inline-formula"><sub>3</sub></span>) with or without NO<span class="inline-formula"><sub>2</sub></span>. In the presence of NO<span class="inline-formula"><sub>2</sub></span>, the SOA yields decreased by more than a factor of 2, but the mass absorption coefficient at 365 nm (MAC<span class="inline-formula"><sub>365</sub></span>) of ind-SOA was 4.3 <span class="inline-formula">±</span> 0.4 m<span class="inline-formula"><sup>2</sup></span> g<span class="inline-formula"><sup>−1</sup></span>, which was 5 times higher than that in experiments without NO<span class="inline-formula"><sub>2</sub></span>. In the presence of NO<span class="inline-formula"><sub>2</sub></span>, C<span class="inline-formula"><sub>8</sub></span>H<span class="inline-formula"><sub>6</sub></span>N<span class="inline-formula"><sub>2</sub></span>O<span class="inline-formula"><sub>2</sub></span> (identified as 3-nitroindole) contributed 76 % to all organic compounds detected by a chemical ionization mass spectrometer, contributing <span class="inline-formula">∼</span> 50 % of the light absorption at 365 nm (Abs<span class="inline-formula"><sub>365</sub></span>). In the absence of NO<span class="inline-formula"><sub>2</sub></span>, the dominating chromophore was C<span class="inline-formula"><sub>8</sub></span>H<span class="inline-formula"><sub>7</sub></span>O<span class="inline-formula"><sub>3</sub></span>N, contributing to 20 %–30 % of Abs<span class="inline-formula"><sub>365</sub></span>. Indole contributes substantially to the formation of secondary BrC and its potential impact on the atmospheric radiative transfer is further enhanced in the presence of NO<span class="inline-formula"><sub>2</sub></span>, as it significantly increases the specific light absorption of ind-SOA by facilitating the formation of 3-nitroindole. This work provides new insights into an important process of brown carbon formation by interaction of two pollutants, NO<span class="inline-formula"><sub>2</sub></span> and indole, mainly emitted by anthropogenic activities.</p> |
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| ISSN: | 1680-7316 1680-7324 |