High precision atmospheric GHG measurements for the Orinoco region: The Villavicencio Tower (VLO)

Abstract. Understanding the dynamics of natural and anthropogenic sources and sinks of greenhouse gases (GHG) is key to projecting anthropogenic climate change and detecting potential climate-carbon feedbacks. While our understanding of the sources and sinks has increased considerably over the past decades, much of the progress has focused on extratropical ecosystems, leaving large parts of the tropics understudied. Tropical ecosystems are assumed to be important carbon sinks and significant sources of methane, but much of the temporal and spatial heterogeneity and trends are still poorly understood. Observational efforts have largely concentrated on key tropical regions such as the Amazon Basin, whereas other tropical areas remain sparsely monitored with in-situ measurements. In particular, northern South America—despite being identified by bottom-up and top-down models as a significant contributor to global GHG budgets—currently lacks atmospheric observations to evaluate these estimates or resolve their spatial and temporal variability. To address this observational gap, here we present the establishment of the Villavicencio Tower (VLO) for atmospheric GHG measurements to provide additional constraints on GHG emission estimates across northern South America. This 26 m tower is located within the Orinoco lowlands, close to the Andean foothills in Colombia. Due to the predominantly easterly winds in the region, the footprint covers the Orinoco basin and the northern Amazon. Weekly duplicated flask measurements are taken, and laboratory analysis of trace gases (CO₂, CH₄, CO, N₂O, SF₆, H₂) and the stable isotope composition of CO₂ (¹³C and ¹⁸O) and CH₄ (¹³C and ²H) are performed, as well as O₂/N₂ and Ar/N₂. The tower started operating on 20 June 2023 and here we present the first 21 months of data. Time series of all measurements are presented as well as a discussion regarding uncertainties. These measurements will allow for improved estimates of GHG emissions across northern South America and to detect long-range transport across the Amazon to the Orinoco river basin.