Investigating carbonyl compounds above the Amazon rainforest using a proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS) with NO<sup>+</sup> chemical ionization
<p>The photochemistry of carbonyl compounds significantly influences tropospheric chemical composition by altering the local oxidative capacity; free radical abundance in the upper troposphere; and formation of ozone, peroxycarboxylic nitric anhydride (PAN), and secondary organic aerosol parti...
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| Main Authors: | , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2024-10-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/24/11883/2024/acp-24-11883-2024.pdf |
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| Summary: | <p>The photochemistry of carbonyl compounds significantly influences tropospheric chemical composition by altering the local oxidative capacity; free radical abundance in the upper troposphere; and formation of ozone, peroxycarboxylic nitric anhydride (PAN), and secondary organic aerosol particles. Carbonyl compounds can be emitted directly from the biosphere into the atmosphere and are formed through photochemical degradation of various precursor compounds. Aldehydes have atmospheric lifetimes of hours to days, whereas ketones persist for up to several weeks. While standard operating conditions for a proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS) using <span class="inline-formula">H<sub>3</sub>O<sup>+</sup></span> ions are unable to separate aldehydes and ketones, the use of <span class="inline-formula">NO<sup>+</sup></span> reagent ions allows for the differential detection of isomeric carbonyl compounds with a high temporal resolution. Here we study the temporal (24 <span class="inline-formula">h</span>) and vertical (80–325 <span class="inline-formula">m</span>) variability of individual carbonyl compounds in the Amazon rainforest atmosphere with respect to their rainforest-specific sources and sinks. We found strong sources of ketones within or just above the canopy (acetone, methyl ethyl ketone (MEK), and <span class="inline-formula">C<sub>5</sub></span> ketones). A common feature of the carbonyls was nocturnal deposition observed by loss rates, most likely since oxidized volatile organic compounds are rapidly metabolized and utilized by the biosphere. With <span class="inline-formula">NO<sup>+</sup></span> chemical ionization, we show that the dominant carbonyl species include acetone and propanal, which are present at a ratio of 1 : 10 in the wet-to-dry transition season and 1 : 20 in the dry season.</p> |
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| ISSN: | 1680-7316 1680-7324 |