New technique for high-precision, simultaneous measurements of CH<sub>4</sub>, N<sub>2</sub>O and CO<sub>2</sub> concentrations; isotopic and elemental ratios of N<sub>2</sub>, O<sub>2</sub> and Ar; and total air content in ice cores by wet extraction
<p>Air in polar ice cores provides unique information on past climatic and atmospheric changes. We developed a new method combining wet extraction, gas chromatography and mass spectrometry for high-precision, simultaneous measurements of eight air components (<span class="inline-formul...
| Main Authors: | , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-12-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://amt.copernicus.org/articles/13/6703/2020/amt-13-6703-2020.pdf |
| Summary: | <p>Air in polar ice cores provides unique information on past climatic and atmospheric changes. We developed a new method combining wet extraction, gas
chromatography and mass spectrometry for high-precision, simultaneous measurements of eight air components (<span class="inline-formula">CH<sub>4</sub></span>, <span class="inline-formula">N<sub>2</sub>O</span> and
<span class="inline-formula">CO<sub>2</sub></span> concentrations; <span class="inline-formula"><i>δ</i></span><span class="inline-formula"><sup>15</sup>N</span>, <span class="inline-formula"><i>δ</i></span><span class="inline-formula"><sup>18</sup>O</span>, <span class="inline-formula"><i>δ</i></span><span class="inline-formula">O<sub>2</sub>∕N<sub>2</sub></span> and <span class="inline-formula"><i>δ</i></span><span class="inline-formula">Ar∕N<sub>2</sub></span>; and total air
content) from an ice-core sample of <span class="inline-formula">∼</span> 60 <span class="inline-formula">g</span>. The ice sample is evacuated for <span class="inline-formula">∼</span> 2 <span class="inline-formula">h</span> and melted under vacuum, and the
released air is continuously transferred into a sample tube at 10 <span class="inline-formula">K</span> within 10 <span class="inline-formula">min</span>. The air is homogenized in the sample tube
overnight at room temperature and split into two aliquots for mass spectrometric and gas chromatographic measurements. Care is taken to minimize
(1) contamination of greenhouse gases by using a long evacuation time, (2) consumption of oxygen during sample storage by a passivation treatment on
sample tubes, and (3) fractionation of isotopic ratios with a long homogenization time for splitting. Precision is assessed by analyzing standard
gases with artificial ice and duplicate measurements of the Dome Fuji and NEEM ice cores. The overall reproducibility (1 SD) of duplicate ice-core
analyses are 3.2 <span class="inline-formula">ppb</span>, 2.2 <span class="inline-formula">ppb</span> and 2.9 <span class="inline-formula">ppm</span> for <span class="inline-formula">CH<sub>4</sub></span>, <span class="inline-formula">N<sub>2</sub>O</span> and <span class="inline-formula">CO<sub>2</sub></span> concentrations;
0.006 ‰, 0.011 ‰, 0.09 ‰ and 0.12 ‰ for <span class="inline-formula"><i>δ</i></span><span class="inline-formula"><sup>15</sup>N</span>, <span class="inline-formula"><i>δ</i></span><span class="inline-formula"><sup>18</sup>O</span>, <span class="inline-formula"><i>δ</i></span><span class="inline-formula">O<sub>2</sub>∕N<sub>2</sub></span>
and <span class="inline-formula"><i>δ</i></span><span class="inline-formula">Ar∕N<sub>2</sub></span>; and 0.63 <span class="inline-formula">mL<sub>STP</sub> kg<sup>−1</sup></span> for total air content, respectively. Our new method successfully combines the
high-precision, small-sample and multiple-species measurements, with a wide range of applications for ice-core paleoenvironmental studies.</p> |
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| ISSN: | 1867-1381 1867-8548 |