A harmonized database of biosphere–atmosphere ammonia flux measurements across ecosystems and pollution regimes

Abstract

Ammonia (NH3) is a trace gas with detrimental effects on human health and ecosystems. Understanding and quantification of NH3 exchange between the biosphere and atmosphere is essential for assessing ecosystem nitrogen budgets and critical load exceedances. Yet, uncertainty in these processes remains significant, due to the global scarcity of measurements. We created a database of more than 40,000 records of NH3 flux measurements across ecosystems, including heathlands, peatlands, grasslands, forests, croplands, and dunes, in areas with varying ambient NH3 and sulphur dioxide concentrations, using different measurement techniques from 1991 to 2024. A significant share of measurements originates from the Netherlands, reflecting its early deployment of a high-resolution NH3 monitoring network. Fluxes are quality controlled and harmonized using consistent algorithms, with uncertainty estimates included. Fluxes were recalculated using consistent stability correction functions, ensuring comparability across sites. By providing this database, we aim to contribute to the understanding of the NH3 biosphere-atmosphere exchange, its environmental controls, the validation and calibration of NH3 exchange schemes, and the characterization of NH3 fluxes across ecosystems.