Short-term variability of atmospheric helium revealed through a cryo-enrichment method
<p>Tropospheric helium variations are tightly linked to <span class="inline-formula">CO<sub>2</sub></span> due to the co-emission of <span class="inline-formula">He</span> and <span class="inline-formula">CO<sub>2<...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2023-03-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://amt.copernicus.org/articles/16/1551/2023/amt-16-1551-2023.pdf |
| Summary: | <p>Tropospheric helium variations are tightly linked to <span class="inline-formula">CO<sub>2</sub></span> due to the co-emission of <span class="inline-formula">He</span> and <span class="inline-formula">CO<sub>2</sub></span> from natural-gas
burning. Recently, Birner et al. (2022a) showed that the global consumption of natural gas has measurably increased the <span class="inline-formula">He</span> content of the
atmosphere. Like <span class="inline-formula">CO<sub>2</sub></span>, <span class="inline-formula">He</span> is also predicted to exhibit complex spatial and temporal variability on shorter timescales, but
measurements of these short-term variations are lacking. Here, we present the development of an improved gas delivery and purification system for the
semi-continuous mass spectrometric measurement of the atmospheric <span class="inline-formula">He</span>-to-nitrogen ratio (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M8" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mi mathvariant="normal">He</mi><mo>/</mo><msub><mi mathvariant="normal">N</mi><mn mathvariant="normal">2</mn></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="35pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="269f5ce6c5ddaee06cc46a97dbf56995"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-16-1551-2023-ie00001.svg" width="35pt" height="14pt" src="amt-16-1551-2023-ie00001.png"/></svg:svg></span></span>). The method replaces the chemical
getter used previously by Birner et al. (2021, 2022a) to preconcentrate <span class="inline-formula">He</span> in an air stream with a cryogenic trap which can be more simply
regenerated by heating and which improves the precision of the measurement to 22 <span class="inline-formula">per meg</span> (i.e., 0.022 ‰) in
10 <span class="inline-formula">min</span> (1<span class="inline-formula"><i>σ</i></span>). Using this “cryo-enrichment” method, we measured the <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M13" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mi mathvariant="normal">He</mi><mo>/</mo><msub><mi mathvariant="normal">N</mi><mn mathvariant="normal">2</mn></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="35pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="de443b31e798bf19b9a0a22e87a0d040"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-16-1551-2023-ie00002.svg" width="35pt" height="14pt" src="amt-16-1551-2023-ie00002.png"/></svg:svg></span></span> ratios in ambient air at La Jolla (California,
USA) over 5 weeks in 2022. During this period, <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M14" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mi mathvariant="normal">He</mi><mo>/</mo><msub><mi mathvariant="normal">N</mi><mn mathvariant="normal">2</mn></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="35pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="3186ebc579eaf02f53bc4eb39bf9fc60"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-16-1551-2023-ie00003.svg" width="35pt" height="14pt" src="amt-16-1551-2023-ie00003.png"/></svg:svg></span></span> was strongly correlated with atmospheric <span class="inline-formula">CO<sub>2</sub></span> concentrations, as expected
from anthropogenic emissions, with a diurnal cycle of 450–500 <span class="inline-formula">per meg</span> (max–min) caused by the sea–land breeze pattern of local winds,
which modulates the influence of local pollution sources.</p> |
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| ISSN: | 1867-1381 1867-8548 |