Find in Library

<p>Mitigation of greenhouse gases requires a precise knowledge of their sources at both global and regional scales. With improving measurement techniques, in situ <span class="inline-formula"><i>δ</i>(¹³C,CH₄)</span> records are analysed in a growing number of studies to characterise methane emissions and to evaluate inventories at regional and local scales. However, most of these studies cover short time periods of a few months, and the results show a large regional variability. In this study, a 6-year time record of in situ <span class="inline-formula"><i>δ</i>(¹³C,CH₄)</span>, measured with a cavity ring-down spectroscopy (CRDS) analyser in Heidelberg, Germany, is analysed to obtain information about seasonal variations and trends of CH<span class="inline-formula">₄</span> emissions. The Keeling plot method is applied to atmospheric measurements on different timescales, and the resulting source contributions are used to evaluate the CH<span class="inline-formula">₄</span> emissions reported by two emission inventories: the Emissions Database for Global Atmospheric Research (EDGAR v6.0) and the inventory of the State Institute for the Environment Baden-Württemberg (LUBW). The mean isotopic carbon source signature for the Heidelberg catchment area derived from atmospheric measurements is <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M5" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>(</mo><mo>-</mo><mn mathvariant="normal">52.3</mn><mspace linebreak="nobreak" width="0.125em"/><mo>±</mo><mspace width="0.125em" linebreak="nobreak"/><mn mathvariant="normal">0.4</mn><mo>)</mo></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="68pt" height="12pt" class="svg-formula" dspmath="mathimg" md5hash="fb5b1c1667b24a3822eb189be200e9a5"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-24-2951-2024-ie00001.svg" width="68pt" height="12pt" src="acp-24-2951-2024-ie00001.png"/></svg:svg></span></span> <span class="inline-formula">‰</span> and shows an annual cycle with <span class="inline-formula">5.8</span> <span class="inline-formula">‰</span> more depleted values in summer than in winter. This annual cycle can only be partly explained by seasonal variations in the <span class="inline-formula">¹³</span>C-enriched emissions from heating and reveals strong seasonal variations in biogenic CH<span class="inline-formula">₄</span> emissions in the Heidelberg catchment area, which are not included in EDGAR v6.0. The comparison with emission inventories also shows that EDGAR v6.0 overestimates the CH<span class="inline-formula">₄</span> emissions from less depleted sources. In situ CH<span class="inline-formula">₄</span> isotope analysers at continental and urban monitoring stations can make an important contribution to the verification and improvement of emission inventories.</p>