Estimation of Dry Deposition of Ammoniacal Nitrogen Using an Inferential Method

Effects of Ammonia Volatilization through Plant Stomata and Surface Wetness on Dry Deposition Velocity

Abstract

The dry deposition of ammoniacal nitrogen (NH_x) on managed turf grassland in Tsukuba, central Japan, was investigated from August 14, 2004 to February 28, 2005. A filer-pack method was employed to measure the weekly mean concentrations of NH₃ and particulate NH⁴⁺ in the atmosphere. An inferential method was applied to estimate the dry deposition velocities of NH₃ and particulate NH⁴⁺, which included the effects of NH₃ emission through plant stomata and surface wetness on the dry deposition velocity of NH₃. The dry deposition of NH_x was calculated by multiplying their atmospheric concentrations by their deposition velocities. As the mean values for NH₃ and particulate NH ⁴⁺, the atmospheric concentrations were 150 and 89 nmol m^-3, the dry deposition velocities were 0.66 and 0.061 cm s^-2, and the dry depositions were 80 and 4 μmol m^-2, d^-1, respectively. The atmospheric concentrations of NH_x were considered to be a typical condition in rural areas. The estimated dry deposition velocity of NH₃ was at the lower limit among the existing studies. The effect of NH₃ emission from plant stomata averagely decreased the mean dry deposition velocity of NH₃ in 0.013 cm s^-1 (2.0 %). On the other hand, the effect of surface wetness averagely increased that in 0.042 cm s^-1 (6.4 %). The degree of annual dry deposition of NH_x converted from the daily means was similar to the wet deposition of NH⁴⁺ in Japan, which showed that dry deposition strongly contributes to the atmospheric deposition of NH_x. The dry deposition velocity of NHx increases in vegetation such as natural grasslands and forests with a larger aerodynamic roughness. Therefore, the contribution of dry deposition to atmospheric deposition of NH_x is likely to enlarge in these natural vegetations.