Volatile organic compound fluxes over a winter wheat field by PTR-Qi-TOF-MS and eddy covariance
<p>Volatile organic compounds (VOCs) contribute to air pollution through the formation of secondary aerosols and ozone and extend the lifetime of methane in the atmosphere. Tropospheric VOCs originate to 90 % from biogenic sources on a global scale, mainly from forests. Crops are also a potent...
| Main Authors: | , , , , , , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2022-03-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/22/2817/2022/acp-22-2817-2022.pdf |
| Summary: | <p>Volatile organic compounds (VOCs) contribute to air
pollution through the formation of secondary aerosols and ozone and extend
the lifetime of methane in the atmosphere. Tropospheric VOCs originate to
90 % from biogenic sources on a global scale, mainly from forests. Crops
are also a potentially large yet poorly characterized source of VOCs (30 %
of the VOC emissions in Europe, mostly oxygenated). In this study, we
investigated VOC fluxes over a winter wheat field by eddy covariance using a
PTR-Qi-TOF-MS with high sensitivity and mass resolution. The study took
place near Paris over a 5-week period and included flowering, crop maturity
and senescence. We found a total of 123 VOCs with fluxes 3 times above
the detection limit. Methanol was the most emitted compound with an average
flux of 63 <span class="inline-formula">µ</span>g m<span class="inline-formula"><sup>−2</sup></span> h<span class="inline-formula"><sup>−1</sup></span>, representing about 52 % of summed
VOC emissions on a molar basis (36 % on a mass basis). We also identified
ethanol, acetone, acetaldehyde and dimethyl sulfide among the six most
emitted compounds. The third most emitted VOC corresponded to the ion <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M4" display="inline" overflow="scroll" dspmath="mathml"><mrow><mi>m</mi><mo>/</mo><mi>z</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="23pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="55e7511b997f0b1e1b80fcef0834494e"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-2817-2022-ie00001.svg" width="23pt" height="14pt" src="acp-22-2817-2022-ie00001.png"/></svg:svg></span></span> 93.033. It was tentatively identified as furan (C<span class="inline-formula"><sub>6</sub></span>H<span class="inline-formula"><sub>4</sub></span>O), a compound
not previously reported to be strongly emitted by crops. The average summed
VOC emissions were about 173 <span class="inline-formula">±</span> 6 <span class="inline-formula">µ</span>g m<span class="inline-formula"><sup>2</sup></span> h<span class="inline-formula"><sup>−1</sup></span>,
while the average VOC depositions were about 109 <span class="inline-formula">±</span> 2 <span class="inline-formula">µ</span>g m<span class="inline-formula"><sup>−2</sup></span> h<span class="inline-formula"><sup>−1</sup></span> and hence 63 % of the VOC emissions on a mass basis. The
net ecosystem flux of VOCs was an emission of 64 <span class="inline-formula">±</span> 6 <span class="inline-formula">µ</span>g m<span class="inline-formula"><sup>−2</sup></span> h<span class="inline-formula"><sup>−1</sup></span> (0.5 <span class="inline-formula">±</span> 0.05 nmol m<span class="inline-formula"><sup>−2</sup></span> s<span class="inline-formula"><sup>−1</sup></span>). The most
deposited VOCs were identified as hydroxyacetone, acetic acid and fragments
of oxidized VOCs. Overall, our results reveal that wheat fields represent a
non-negligible source and sink of VOCs to be considered in regional VOC
budgets and underline the usefulness and limitations of eddy covariance
measurements with a PTR-Qi-TOF-MS.</p> |
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| ISSN: | 1680-7316 1680-7324 |