Airborne Measurements Reveal High Spatiotemporal Variation and the Heavy-Tail Characteristic of Nitrous Oxide Emissions in Iowa

Abstract

Nitrous oxide (N₂O) emissions from croplands contribute substantially to the climate impact of agriculture. Emissions of N₂O are controlled by both anthropogenic and environmental factors and can vary by orders of magnitude over short times and distances. This nature of emissions is difficult to capture with models and presents an observational challenge. In the 2021 and 2022 growing season, we collected airborne measurements of N₂O over Iowa to characterize N₂O emissions at the farm to multi-county spatial scales across days. We link our airborne observations to surface emissions using a Lagrangian particle dispersion model and quantify emissions using a Bayesian inversion framework. We find emissions magnitudes across Iowa, showing greater skew than modeled predictions, with a small fraction of fields contributing disproportionately to the total [25% of the domain contributing to 52%–77% of total emissions]. In addition to the high spatial variation, we find high temporal variability between flight days by a factor of 2 at the 100 km scale, and an order of magnitude at the 2 km scale], with peak emissions occurring at median soil moisture. This work illustrates the importance of transient, intense emissions from concentrated areas in explaining total cropland emissions, and demonstrates how airborne measurements can provide insights into variation that may be missed by other observational systems. Investigation into environmental factors highlights the need for observations, models and their input data to be spatiotemporally resolved to enable direct comparison, facilitating evaluation of predicted and reported emissions and providing guidance and feedback on mitigation strategies.