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Marine emissions and trade winds control the atmospheric nitrous oxide in the Galapagos Islands

Abstract:

Nitrous oxide (N<inf>2</inf>O) is a potent greenhouse gas emitted by oceanic and terrestrial sources, and its biogeochemical cycle is influenced by both natural processes and anthropogenic activities. Current atmospheric N<inf>2</inf>O monitoring networks, including tall-tower and flask measurements, often overlook major marine hotspots, such as the eastern tropical Pacific Ocean. We present the first 15 months of high-frequency continuous measurements of N<inf>2</inf>O and carbon monoxide from the newly established Galapagos Emissions Monitoring Station in the region. Over this period, N<inf>2</inf>O mole fractions vary by approximately 5 ppb, influenced by seasonal trade winds, local anthropogenic emissions, and air masses transported from marine N<inf>2</inf>O emission hotspots. Notably, between February and April 2024, we observe high variability linked to the southward shift of the intertropical convergence zone and weakened trade winds over the Galapagos Islands. Increased variability during this period is driven by stagnant local winds, which accumulate emissions, and the mixing of air masses with different N<inf>2</inf>O contents from the Northern Hemisphere and the Southern Hemisphere. The remaining variability is primarily due to differences in air mass transport and heterogeneity in surface fluxes from the eastern tropical Pacific. Air masses passing over the Peruvian and Chilean upwelling systems – key sources of oceanic N<inf>2</inf>O efflux – show markedly higher N<inf>2</inf>O mole fractions at the station.