On the diurnal and field-scale variability of atmospheric ammonia over Dutch grasslands

Summary

Excess nitrogen deposition, particularly deposition of atmospheric ammonia (NH₃), not only leads to environmental damage, but there are also serious political and societal consequences when mitigation of these harmful effects fails. We present a comprehensive approach to advance our understanding of the diurnal variability of both the NH₃ concentration and surface-atmosphere exchange, combining advanced observations with turbulent resolved simulations at field-scale. The variability of atmospheric NH₃ is governed by processes acting on local and non-local scales, spanning several disciplines, including meteorology, biology and chemistry. We furthermore identify a mismatch between the observed and parameterized NH₃ flux at subdaily scales. To advance our understanding of this NH₃ exchange, we connect NH₃ flux observations to CO₂ uptake and plant transpiration. In doing so, we are able to link observed NH₃ emissions to stomatal exchange. We furthermore assess the impact of nearby emissions on NH₃ measurements. Using a high-resolution turbulent resolved simulation framework, we find that an emission plume can affect NH₃ measurements over several (1-4) kilometers distance. With our integrated approach and turbulent resolved simulation framework, we are taking research on atmospheric ammonia to a higher level of quantification and detail.