Intercomparison of O₂ ∕ N₂ ratio scales among AIST, NIES, TU, and SIO based on a round-robin exercise using gravimetric standard mixtures

• Main Authors: N. Aoki, S. Ishidoya, Y. Tohjima, S. Morimoto, R. F. Keeling, A. Cox, S. Takebayashi, S. Murayama
• Format: Article
• Language: English
• Published: Copernicus Publications 2021-09-01
• Series: Atmospheric Measurement Techniques
• Online Access: https://amt.copernicus.org/articles/14/6181/2021/amt-14-6181-2021.pdf

<p>A study was conducted to compare the <span class="inline-formula"><i>δ</i></span>(<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M8" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi mathvariant="normal">O</mi><mn mathvariant="normal">2</mn></msub><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="34pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="4429455449d1e061d22bb9828b35172e"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-14-6181-2021-ie00004.svg" width="34pt" height="14pt" src="amt-14-6181-2021-ie00004.png"/></svg:svg></span></span>) scales used by four laboratories engaged in atmospheric <span class="inline-formula"><i>δ</i></span>(<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M10" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi mathvariant="normal">O</mi><mn mathvariant="normal">2</mn></msub><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="34pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="6f7587bd10895708ba7d22e72927ea31"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-14-6181-2021-ie00005.svg" width="34pt" height="14pt" src="amt-14-6181-2021-ie00005.png"/></svg:svg></span></span>) measurements. These laboratories are the Research Institute for Environmental Management Technology, Advanced Industrial Science and Technology (EMRI/AIST); the National Institute for Environmental Studies (NIES); Tohoku University (TU); and Scripps Institution of Oceanography (SIO). Therefore, five high-precision standard mixtures for the <span class="inline-formula">O₂</span> molar fraction gravimetrically prepared by the National Metrology Institute of Japan, AIST (NMIJ/AIST) with a standard uncertainty of less than 5 per meg (0.001 ‰) were used as round-robin standard mixtures. EMRI/AIST, NIES, TU, and SIO reported the analyzed values of the standard mixtures on their own <span class="inline-formula"><i>δ</i></span>(<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M13" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi mathvariant="normal">O</mi><mn mathvariant="normal">2</mn></msub><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="34pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="cd52a973eaa097d6d6db5b9dfa3ab1f6"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-14-6181-2021-ie00006.svg" width="34pt" height="14pt" src="amt-14-6181-2021-ie00006.png"/></svg:svg></span></span>) scales, and the values were compared with the <span class="inline-formula"><i>δ</i></span>(<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M15" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi mathvariant="normal">O</mi><mn mathvariant="normal">2</mn></msub><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="34pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="b1374199d4ad746bc8cf74082403b011"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-14-6181-2021-ie00007.svg" width="34pt" height="14pt" src="amt-14-6181-2021-ie00007.png"/></svg:svg></span></span>) values gravimetrically determined by NMIJ/AIST (the NMIJ/AIST scale). The <span class="inline-formula"><i>δ</i></span>(<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M17" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi mathvariant="normal">O</mi><mn mathvariant="normal">2</mn></msub><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="34pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="b120a71f26559d455c27ecdd0aa250e8"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-14-6181-2021-ie00008.svg" width="34pt" height="14pt" src="amt-14-6181-2021-ie00008.png"/></svg:svg></span></span>) temporal drift in the five standard mixtures during the intercomparison experiment from May 2017 to March 2020 was corrected based on the <span class="inline-formula"><i>δ</i></span>(<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M19" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi mathvariant="normal">O</mi><mn mathvariant="normal">2</mn></msub><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="34pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="0e8fa2039bc0f930a8484ff4c503d83e"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-14-6181-2021-ie00009.svg" width="34pt" height="14pt" src="amt-14-6181-2021-ie00009.png"/></svg:svg></span></span>) values analyzed before and after the laboratory measurements by EMRI/AIST. The scales are compared based on offsets in zero and span. The relative span offsets of EMRI/AIST, TU, NIES, and SIO scales against the NMIJ/AIST scale were <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M20" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><mn mathvariant="normal">0.11</mn><mspace linebreak="nobreak" width="0.125em"/><mi mathvariant="italic">%</mi><mo>±</mo><mn mathvariant="normal">0.10</mn><mspace linebreak="nobreak" width="0.125em"/><mi mathvariant="italic">%</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="86pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="55151ea446fa5dbe4aa98c5fdfd10416"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-14-6181-2021-ie00010.svg" width="86pt" height="10pt" src="amt-14-6181-2021-ie00010.png"/></svg:svg></span></span>, <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M21" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><mn mathvariant="normal">0.10</mn><mspace linebreak="nobreak" width="0.125em"/><mi mathvariant="italic">%</mi><mo>±</mo><mn mathvariant="normal">0.13</mn><mspace linebreak="nobreak" width="0.125em"/><mi mathvariant="italic">%</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="86pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="7c45274119b9672c9fca5ff4e9b37784"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-14-6181-2021-ie00011.svg" width="86pt" height="10pt" src="amt-14-6181-2021-ie00011.png"/></svg:svg></span></span>, <span class="inline-formula">3.39 <i>%</i>±0.13 <i>%</i></span>, and <span class="inline-formula">0.93 <i>%</i>±0.10 <i>%</i></span>, respectively. The largest offset corresponded to a 0.30 <span class="inline-formula">Pg yr⁻¹</span> decrease and increase in global estimates for land biospheric and oceanic <span class="inline-formula">CO₂</span> uptakes based on trends in atmospheric <span class="inline-formula">CO₂</span> and <span class="inline-formula"><i>δ</i></span>(<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M28" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi mathvariant="normal">O</mi><mn mathvariant="normal">2</mn></msub><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="34pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="e20398d2b66e20262265917023978e6c"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-14-6181-2021-ie00012.svg" width="34pt" height="14pt" src="amt-14-6181-2021-ie00012.png"/></svg:svg></span></span>). The deviations in the measured <span class="inline-formula"><i>δ</i></span>(<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M30" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi mathvariant="normal">O</mi><mn mathvariant="normal">2</mn></msub><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="34pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="540803178710422aa30fda95d6b2f342"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-14-6181-2021-ie00013.svg" width="34pt" height="14pt" src="amt-14-6181-2021-ie00013.png"/></svg:svg></span></span>) values on the laboratory scales from the NMIJ/AIST scale are <span class="inline-formula">65.8±2.2</span>, <span class="inline-formula">425.7±3.1</span>, <span class="inline-formula">404.5±3.0</span>, and <span class="inline-formula">596.4±2.4</span> per meg for EMRI/AIST, TU, NIES, and SIO, respectively. The difference between atmospheric <span class="inline-formula"><i>δ</i></span>(<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M36" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi mathvariant="normal">O</mi><mn mathvariant="normal">2</mn></msub><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="34pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="4ee12ebe2a434297f77c4d84f5c158ed"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-14-6181-2021-ie00014.svg" width="34pt" height="14pt" src="amt-14-6181-2021-ie00014.png"/></svg:svg></span></span>) values observed at Hateruma Island (HAT; 24.05<span class="inline-formula">^∘</span> N, 123.81<span class="inline-formula">^∘</span> E), Japan, by EMRI/AIST and NIES were reduced from <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M39" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><mn mathvariant="normal">329.3</mn><mo>±</mo><mn mathvariant="normal">6.9</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="64pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="635324115bf82d101c6ca08e180cc9d4"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-14-6181-2021-ie00015.svg" width="64pt" height="10pt" src="amt-14-6181-2021-ie00015.png"/></svg:svg></span></span> to <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M40" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><mn mathvariant="normal">6.6</mn><mo>±</mo><mn mathvariant="normal">6.8</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="52pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="75874885cf30c22ac60910eca30d559b"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-14-6181-2021-ie00016.svg" width="52pt" height="10pt" src="amt-14-6181-2021-ie00016.png"/></svg:svg></span></span> per meg by converting their scales to the NMIJ/AIST scale.</p>