Dataset supporting the manuscript: "Aerodynamic flux–gradient measurements of ammonia over four spring seasons in grazed grassland: environmental drivers, methodological challenges and uncertainties" by Abdulwahab et al. (Biogeosciences, 2025)

Measurements of atmospheric ammonia fluxes over grazed grassland The dataset documents the measurements made over a pasture in NW France to characterise ammonia (NH3) emissions by grazing cattle over grassland. NH3 concentrations were measured at up to five heights (typically 0.1–2.1 m) using a gradient-lift ammonia sampling system. Turbulence and meteorological variables (wind speed, friction velocity, temperature, and relative humidity) were measured on site. NH3 fluxes were derived using the aerodynamic flux-gradient (AGM) approach following Flechard and Fowler (1998), with quality-controlled characterization of the measurements. The experimental field was divided into two 2.35-hectare halves: the northwest (Plot A) and southeast (Plot B) sections. The Kormann and Meixner (2001) footprint model was used to estimate the relative contribution of each plot to the measured fluxes. Fluxes under southwest to northwest wind directions were attributed to Plot A, while those under northeast to southeast winds were attributed to Plot B. All data files include units in the second row of each column. Files and Contents -------------------------------------------------------------------------------- 1. Vegetation.xlsx Contains biomass, bulk herbage nitrogen (N) content, leaf area index (LAI) measured before grazing events, and canopy height measurements taken both before and after each grazing event. 2. Fertilisation_Cuts.xlsx Contains grassland management records i.e., fertilizer applications and cutting events for both plots (A and B). 3. Soil_Nmin.xlsx Contains soil sampling dates and concentrations of mineral nitrogen i.e. nitrate (NO3-) and ammonium (NH4+), measured at the field scale, with replicate numbers specified for each sampling day. 4. Fluxes_Met_Micromet_plots_A_B_2021-2024.xlsx Contains semi-continuous records of half-hourly micro-meteorological and NH3 flux data for four spring seasons (2021-2024). - Plot_A: flux observations primarily influenced by Plot A (under SW–NW wind sectors). - Plot_B: flux observations primarily influenced by Plot B (under NE–SE wind sectors). Units are specified in the second row of each column. References -------------------------------------------------------------------------------- Flechard, C. R. and Fowler, D.: Atmospheric ammonia at a moorland site. II: Long-term surface-atmosphere micrometeorological flux measurements, Q. J. Roy. Meteor. Soc., 124, 759–791, 1998. Kormann, R., and Meixner, F. X.: An analytical footprint model for non-neutral stratification, Bound.-Lay. Meteorol., 99,207–224, https://doi.org/10.1023/A:1018991015119, 2001.