Influence of ambient NO and NO<sub>2</sub> on the quantification of total peroxy nitrates (ΣPNs) and total alkyl nitrates (ΣANs) by thermal dissociation cavity ring-down spectroscopy (TD-CRDS)
<p>Measurement of total peroxy nitrates (<span class="inline-formula">Σ</span>PNs) and alkyl nitrates (<span class="inline-formula">Σ</span>ANs) by instruments that use thermal dissociation (TD) inlets to convert the organic nitrate to detectable NO&...
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| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2025-04-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://amt.copernicus.org/articles/18/1943/2025/amt-18-1943-2025.pdf |
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| Summary: | <p>Measurement of total peroxy nitrates (<span class="inline-formula">Σ</span>PNs) and alkyl nitrates (<span class="inline-formula">Σ</span>ANs) by instruments that use thermal dissociation (TD) inlets to convert the organic nitrate to detectable NO<span class="inline-formula"><sub>2</sub></span> may suffer from systematic bias (both positive and negative) resulting from unwanted secondary chemistry in the heated inlets. Here we review the sources of the bias and the methods used to reduce it and/or correct for it and report new experiments using (for the first time) atmospherically relevant, unsaturated, biogenic alkyl nitrates as well as two different peroxyacetyl nitrate (PAN) sources. We show that the commonly used commercial C<span class="inline-formula"><sub>3</sub></span> alkyl nitrate (isopropyl nitrate, IPN) for characterising the chemistry of ANs is not appropriate for real-air samples that contain longer-chain nitrates. Mixing ratios of ANs generated in the NO<span class="inline-formula"><sub>3</sub></span>-induced oxidation of limonene are strongly positively biased in the presence of NO. By detecting NO<span class="inline-formula"><sub><i>x</i></sub></span> rather than NO<span class="inline-formula"><sub>2</sub></span>, we provide a simple solution to avoid the bias caused by the conversion of NO to NO<span class="inline-formula"><sub>2</sub></span> by primary and secondary peroxy radicals resulting from the complex chemistry in the thermal degradation of long-chain, alkyl nitrates in air at TD temperatures. We also show that using a photochemical source of PAN to characterise the TD inlets can result in a much stronger apparent bias from NO to NO<span class="inline-formula"><sub>2</sub></span> conversion than for a diffusion source of synthesised (“pure”) PAN at similar mixing ratios, especially if high acetone concentrations (and thus radical concentrations) are involved. This is explained by the presence of thermally labile trace gases such as peracetic acid (CH<span class="inline-formula"><sub>3</sub></span>C(O)OOH) and hydrogen peroxide (H<span class="inline-formula"><sub>2</sub></span>O<span class="inline-formula"><sub>2</sub></span>).</p> |
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| ISSN: | 1867-1381 1867-8548 |