This work explores how atmospheric methane sinks (chlorine radical and hydroxyl radical) vary spatially and temporally through the study of carbon monoxide isotope measurements, which are a powerful tracer for determining methane oxidation pathways where chlorine radicals and hydroxyl radicals can’t be measured directly. This important foundational work will provide a powerful data set to constrain atmospheric models that are essential for understanding methane removal pathways and processes. This project includes collaboration with the international FETCH4 project for collection of samples at key study sites.