Land Use Specific Ammonia Deposition Velocities: a Review of Recent Studies (2004-2013)

Land use specific deposition velocities of atmospheric trace gases and aerosols-particularly of reactive nitrogen compounds-are a fundamental input variable for a variety of deposition models. Although the concept is known to have shortcomings-especially with regard to bi-directional exchange-the often limited availability of concentration data and meteorological input variables make it a valuable simplification for regional modeling of deposition fluxes. In order to meet the demand for an up-to-date overview of recent publications on measurements and modeling studies, we compiled a database of ammonia (NH₃) deposition velocities published from 2004 to 2013. Observations from a total of 42 individual studies were averaged using an objective weighing scheme and classified into seven land use categories. Weighted average and median deposition velocities are 2.2 and 2.1 cm s^-1 for coniferous forests, 1.5 and 1.2 cm s^-1 for mixed forests, 1.1 and 0.9 cm s^-1 for deciduous forests, 0.9 and 0.7 cm s^-1 for semi-natural sites, 0.7 and 0.8 cm s^-1 for urban sites, 0.7 and 0.6 cm s^-1 for water surfaces, and 1.0 and 0.4 cm s^-1 for agricultural sites, respectively. Thus, values presented in this compilation were considerably lower than those found in former studies (e.g., VDI 2006). Reasons for the mismatch were likely due to different land use classification, different averaging methods, choices of measurement locations, and improvements in measurement and in modeling techniques. Both data and code used for processing are made available as supplementary material to this article.