<p>Radiocarbon in atmospheric methane (&#916;<sup>14</sup>CH<sub>4</sub>) is a powerful tracer of fossil methane emissions and can be used to attribute methane emissions to fossil or biogenic sources. However, few &#916;<sup>14</sup>CH<sub>4 </sub>measurements are reported since 2000<sup>1,2</sup>, due to challenges in sampling enough carbon for <sup>14</sup>C measurements and in assessing the influence of <sup>14</sup>C emissions from nuclear power plants on the <sup>14</sup>C observations.</p><p>At Imperial College London we addressed the sampling limitation by developing a unique sampling system that separates carbon at the point of sampling and uses small traps of molecular sieves. Collection of a sample is made by three main steps: 1) removal of CO<sub>2</sub> and CO from air, 2) combustion of CH<sub>4</sub> into CO<sub>2</sub> and 3) adsorption of the combustion-derived CO<sub>2</sub> onto the molecular sieve trap. <sup>14</sup>C analysis of our samples was carried out at the accelerator mass spectrometry facility at UCI. This novel system has been used for collection of samples in central London and has been made portable for collection of samples in different settings.&#160;</p><p>Here we describe the system and report the evaluation of the measurement uncertainty and the processing blank. We achieved a measurement precision of 6 &#8240;, which is similar to or better than the reported precision of the most recent observations<sup>1,3</sup>.</p><p><sup>1</sup> Townsend&#8208;Small et al JGR 117(D7) 2012</p><p><sup>2</sup> Sparrow et al Sci. Adv 4(1) 2018</p><p><sup>3</sup> Espic et al Radiocarbon 61( 5) 2019</p>