Disentangling methane and carbon dioxide sources and transport across the Russian Arctic from aircraft measurements

A more accurate characterization of the sources and sinks of methane (CH4) and carbon dioxide (CO2) in the vulnerable Arctic environment is required to better predict climate change. A large-scale aircraft campaign took place in September 2020 focusing on the Siberian Arctic coast. CH4 and CO2 were measured in situ during the campaign and form the core of this study. Measured ozone (O3) and carbon monoxide (CO) are used here as tracers. Median CH4 mixing ratios are fairly higher than the monthly mean hemispheric reference (Mauna Loa, Hawaii, US) with 1890–1969 ppb vs. 1887 ppb respectively, while CO2 mixing ratios from all flights are lower (408.09–411.50 ppm vs. 411.52 ppm). We also report on three case studies. Our analysis suggests that during the campaign the European part of Russia's Arctic and western Siberia were subject to long-range transport of polluted air masses, while the east was mainly under the influence of local emissions of greenhouse gases. The relative contributions of the main anthropogenic and natural sources of CH4 are simulated using the Lagrangian model FLEXPART in order to identify dominant sources in the boundary layer and in the free troposphere. On western terrestrial flights, air mass composition is influenced by emissions from wetlands and anthropogenic activities (waste management, fossil fuel industry, and to a lesser extent the agricultural sector), while in the east, emissions are dominated by freshwater, wetlands, and the oceans, with a likely contribution from anthropogenic sources related to fossil fuels. Our results highlight the importance of the contributions from freshwater and ocean emissions. Considering the large uncertainties associated with them, our study suggests that the emissions from these aquatic sources should receive more attention in Siberia.