Find in Library

<p>In-flight measurements of atmospheric methane (CH<span class="inline-formula">_4(a)</span>) and mass balance flux quantification studies can assist with verification and improvement in the UNFCCC National Inventory reported CH<span class="inline-formula">₄</span> emissions. In the Surat Basin gas fields, Queensland, Australia, coal seam gas (CSG) production and cattle farming are two of the major sources of CH<span class="inline-formula">₄</span> emissions into the atmosphere. Because of the rapid mixing of adjacent plumes within the convective boundary layer, spatially attributing CH<span class="inline-formula">_4(a)</span> mole fraction readings to one or more emission sources is difficult.</p> <p>The primary aims of this study were to use the CH<span class="inline-formula">_4(a)</span> isotopic composition (<span class="inline-formula"><i>δ</i>¹³</span>C<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M7" display="inline" overflow="scroll" dspmath="mathml"><msub><mi/><mrow class="chem"><msub><mi mathvariant="normal">CH</mi><mrow><mn mathvariant="normal">4</mn><mo>(</mo><mi mathvariant="normal">a</mi><mo>)</mo></mrow></msub></mrow></msub></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="11pt" class="svg-formula" dspmath="mathimg" md5hash="29e450b2185d7e009d3253e27f2beb9b"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-15527-2022-ie00001.svg" width="24pt" height="11pt" src="acp-22-15527-2022-ie00001.png"/></svg:svg></span></span>) of in-flight atmospheric air (IFAA) samples to assess where the bottom–up (BU) inventory developed specifically for the region was well characterised and to identify gaps in the BU inventory (missing sources or over- and underestimated source categories). Secondary aims were to investigate whether IFAA samples collected downwind of predominantly similar inventory sources were useable for characterising the isotopic signature of CH<span class="inline-formula">₄</span> sources (<span class="inline-formula"><i>δ</i>¹³</span>C<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M10" display="inline" overflow="scroll" dspmath="mathml"><msub><mi/><mrow class="chem"><msub><mi mathvariant="normal">CH</mi><mrow><mn mathvariant="normal">4</mn><mo>(</mo><mi mathvariant="normal">s</mi><mo>)</mo></mrow></msub></mrow></msub></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="11pt" class="svg-formula" dspmath="mathimg" md5hash="50fd165acb112af532709bb01d4f2b43"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-15527-2022-ie00002.svg" width="24pt" height="11pt" src="acp-22-15527-2022-ie00002.png"/></svg:svg></span></span>) and to identify mitigation opportunities.</p> <p>IFAA samples were collected between 100–350 m above ground level (m a.g.l.) over a 2-week period in September 2018. For each IFAA sample the 2 h back-trajectory footprint area was determined using the NOAA HYSPLIT atmospheric trajectory modelling application. IFAA samples were gathered into sets, where the 2 h upwind BU inventory had <span class="inline-formula">&gt;</span> 50 % attributable to a single predominant CH<span class="inline-formula">₄</span> source (CSG, grazing cattle, or cattle feedlots). Keeling models were globally fitted to these sets using multiple regression with shared parameters (background-air CH<span class="inline-formula">_4(b)</span> and <span class="inline-formula"><i>δ</i>¹³</span>C<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M15" display="inline" overflow="scroll" dspmath="mathml"><msub><mi/><mrow class="chem"><msub><mi mathvariant="normal">CH</mi><mrow><mn mathvariant="normal">4</mn><mo>(</mo><mi mathvariant="normal">b</mi><mo>)</mo></mrow></msub></mrow></msub></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="11pt" class="svg-formula" dspmath="mathimg" md5hash="051a4f4788e9a4b4d08e9faf18be45b9"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-15527-2022-ie00003.svg" width="24pt" height="11pt" src="acp-22-15527-2022-ie00003.png"/></svg:svg></span></span>).</p> <p>For IFAA samples collected from 250–350 m a.g.l. altitude, the best-fit <span class="inline-formula"><i>δ</i>¹³</span>C<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M17" display="inline" overflow="scroll" dspmath="mathml"><msub><mi/><mrow class="chem"><msub><mi mathvariant="normal">CH</mi><mrow><mn mathvariant="normal">4</mn><mo>(</mo><mi mathvariant="normal">s</mi><mo>)</mo></mrow></msub></mrow></msub></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="11pt" class="svg-formula" dspmath="mathimg" md5hash="c4bdc0d44088613b264651085c36c5ea"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-15527-2022-ie00004.svg" width="24pt" height="11pt" src="acp-22-15527-2022-ie00004.png"/></svg:svg></span></span> signatures compare well with the ground observation: CSG <span class="inline-formula"><i>δ</i>¹³</span>C<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M19" display="inline" overflow="scroll" dspmath="mathml"><msub><mi/><mrow class="chem"><msub><mi mathvariant="normal">CH</mi><mrow><mn mathvariant="normal">4</mn><mo>(</mo><mi mathvariant="normal">s</mi><mo>)</mo></mrow></msub></mrow></msub></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="11pt" class="svg-formula" dspmath="mathimg" md5hash="1985b032107569f7e1e0124a4d9098d2"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-15527-2022-ie00005.svg" width="24pt" height="11pt" src="acp-22-15527-2022-ie00005.png"/></svg:svg></span></span> of <span class="inline-formula">−55.4</span> ‰ (confidence interval (CI) 95 % <span class="inline-formula">±</span> 13.7 ‰) versus <span class="inline-formula"><i>δ</i>¹³</span>C<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M23" display="inline" overflow="scroll" dspmath="mathml"><msub><mi/><mrow class="chem"><msub><mi mathvariant="normal">CH</mi><mrow><mn mathvariant="normal">4</mn><mo>(</mo><mi mathvariant="normal">s</mi><mo>)</mo></mrow></msub></mrow></msub></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="11pt" class="svg-formula" dspmath="mathimg" md5hash="6388f302c40c51d5a8a55c8ca67c9b61"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-15527-2022-ie00006.svg" width="24pt" height="11pt" src="acp-22-15527-2022-ie00006.png"/></svg:svg></span></span> of <span class="inline-formula">−56.7</span> ‰ to <span class="inline-formula">−</span>45.6 ‰; grazing cattle <span class="inline-formula"><i>δ</i>¹³</span>C<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M27" display="inline" overflow="scroll" dspmath="mathml"><msub><mi/><mrow class="chem"><msub><mi mathvariant="normal">CH</mi><mrow><mn mathvariant="normal">4</mn><mo>(</mo><mi mathvariant="normal">s</mi><mo>)</mo></mrow></msub></mrow></msub></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="11pt" class="svg-formula" dspmath="mathimg" md5hash="92601f447d0047ce3a816aec8ec2c063"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-15527-2022-ie00007.svg" width="24pt" height="11pt" src="acp-22-15527-2022-ie00007.png"/></svg:svg></span></span> of <span class="inline-formula">−60.5</span> ‰ (CI 95 % <span class="inline-formula">±</span> 15.6 ‰) versus <span class="inline-formula">−</span>61.7 ‰ to <span class="inline-formula">−</span>57.5 ‰. For cattle feedlots, the derived <span class="inline-formula"><i>δ</i>¹³</span>C<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M33" display="inline" overflow="scroll" dspmath="mathml"><msub><mi/><mrow class="chem"><msub><mi mathvariant="normal">CH</mi><mrow><mn mathvariant="normal">4</mn><mo>(</mo><mi mathvariant="normal">s</mi><mo>)</mo></mrow></msub></mrow></msub></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="11pt" class="svg-formula" dspmath="mathimg" md5hash="a77a1c7b13535af33dec50c54cd113eb"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-15527-2022-ie00008.svg" width="24pt" height="11pt" src="acp-22-15527-2022-ie00008.png"/></svg:svg></span></span> (<span class="inline-formula">−</span>69.6 ‰, CI 95 % <span class="inline-formula">±</span> 22.6 ‰), was isotopically lighter than the ground-based study (<span class="inline-formula"><i>δ</i>¹³</span>C<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M37" display="inline" overflow="scroll" dspmath="mathml"><msub><mi/><mrow class="chem"><msub><mi mathvariant="normal">CH</mi><mrow><mn mathvariant="normal">4</mn><mo>(</mo><mi mathvariant="normal">s</mi><mo>)</mo></mrow></msub></mrow></msub></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="11pt" class="svg-formula" dspmath="mathimg" md5hash="16d65df98b9bca7d58155fb086bc3e70"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-15527-2022-ie00009.svg" width="24pt" height="11pt" src="acp-22-15527-2022-ie00009.png"/></svg:svg></span></span> from <span class="inline-formula">−65.2</span> ‰ to <span class="inline-formula">−60.3</span> ‰) but within agreement given the large uncertainty for this source. For IFAA samples collected between 100–200 m a.g.l. the <span class="inline-formula"><i>δ</i>¹³</span>C<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M41" display="inline" overflow="scroll" dspmath="mathml"><msub><mi/><mrow class="chem"><msub><mi mathvariant="normal">CH</mi><mrow><mn mathvariant="normal">4</mn><mo>(</mo><mi mathvariant="normal">s</mi><mo>)</mo></mrow></msub></mrow></msub></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="11pt" class="svg-formula" dspmath="mathimg" md5hash="1ee707675ebbfff6fe174a923bacbfb7"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-15527-2022-ie00010.svg" width="24pt" height="11pt" src="acp-22-15527-2022-ie00010.png"/></svg:svg></span></span> signature for the CSG set (<span class="inline-formula">−</span>65.4 ‰, CI 95 % <span class="inline-formula">±</span> 13.3 ‰) was isotopically lighter than expected, suggesting a BU inventory knowledge gap or the need to extend the population statistics for CSG <span class="inline-formula"><i>δ</i>¹³</span>C<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M45" display="inline" overflow="scroll" dspmath="mathml"><msub><mi/><mrow class="chem"><msub><mi mathvariant="normal">CH</mi><mrow><mn mathvariant="normal">4</mn><mo>(</mo><mi mathvariant="normal">s</mi><mo>)</mo></mrow></msub></mrow></msub></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="11pt" class="svg-formula" dspmath="mathimg" md5hash="66107370c7e89259bee720344d1c3f46"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-15527-2022-ie00011.svg" width="24pt" height="11pt" src="acp-22-15527-2022-ie00011.png"/></svg:svg></span></span> signatures. For the 100–200 m a.g.l. set collected over grazing cattle districts the <span class="inline-formula"><i>δ</i>¹³</span>C<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M47" display="inline" overflow="scroll" dspmath="mathml"><msub><mi/><mrow class="chem"><msub><mi mathvariant="normal">CH</mi><mrow><mn mathvariant="normal">4</mn><mo>(</mo><mi mathvariant="normal">s</mi><mo>)</mo></mrow></msub></mrow></msub></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="11pt" class="svg-formula" dspmath="mathimg" md5hash="70261d2356711f842c404b3f3fafb123"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-15527-2022-ie00012.svg" width="24pt" height="11pt" src="acp-22-15527-2022-ie00012.png"/></svg:svg></span></span> signature (<span class="inline-formula">−</span>53.8 ‰, CI 95 % <span class="inline-formula">±</span> 17.4 ‰) was heavier than expected from the BU inventory. An isotopically light set had a low <span class="inline-formula"><i>δ</i>¹³</span>C<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M51" display="inline" overflow="scroll" dspmath="mathml"><msub><mi/><mrow class="chem"><msub><mi mathvariant="normal">CH</mi><mrow><mn mathvariant="normal">4</mn><mo>(</mo><mi mathvariant="normal">s</mi><mo>)</mo></mrow></msub></mrow></msub></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="11pt" class="svg-formula" dspmath="mathimg" md5hash="69dd80e30c811bfc9b351850f4381ca3"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-15527-2022-ie00013.svg" width="24pt" height="11pt" src="acp-22-15527-2022-ie00013.png"/></svg:svg></span></span> signature of <span class="inline-formula">−</span>80.2 ‰ (CI 95 % <span class="inline-formula">±</span> 4.7 ‰). A CH<span class="inline-formula">₄</span> source with this low <span class="inline-formula"><i>δ</i>¹³</span>C<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M56" display="inline" overflow="scroll" dspmath="mathml"><msub><mi/><mrow class="chem"><msub><mi mathvariant="normal">CH</mi><mrow><mn mathvariant="normal">4</mn><mo>(</mo><mi mathvariant="normal">s</mi><mo>)</mo></mrow></msub></mrow></msub></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="11pt" class="svg-formula" dspmath="mathimg" md5hash="d9498192e18d1aa449d9fb47e4566625"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-15527-2022-ie00014.svg" width="24pt" height="11pt" src="acp-22-15527-2022-ie00014.png"/></svg:svg></span></span> signature has not been incorporated into existing BU inventories for the region. Possible sources include termites and CSG brine ponds. If the excess emissions are from the brine ponds, they can potentially be mitigated. It is concluded that in-flight atmospheric <span class="inline-formula"><i>δ</i>¹³</span>C<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M58" display="inline" overflow="scroll" dspmath="mathml"><msub><mi/><mrow class="chem"><msub><mi mathvariant="normal">CH</mi><mrow><mn mathvariant="normal">4</mn><mo>(</mo><mi mathvariant="normal">a</mi><mo>)</mo></mrow></msub></mrow></msub></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="11pt" class="svg-formula" dspmath="mathimg" md5hash="621137ea4c5feae857e987abffa28c5f"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-15527-2022-ie00015.svg" width="24pt" height="11pt" src="acp-22-15527-2022-ie00015.png"/></svg:svg></span></span> measurements used in conjunction with endmember mixing modelling of CH<span class="inline-formula">₄</span> sources are powerful tools for BU inventory verification.</p>