Monitoring and Modelling of Ammonia Concentrations and Deposition in Agricultural Areas of The Netherlands

Abstract

Passive samplers were used from 1996 to 1999 in a dense network to monitorthe concentrations of ammonia in air, in four agricultural areas in The Netherlands. To show representative patterns, sampling was not made within 50 m of livestock buildings and stores. The concentration of ammonia varies typically between 10 and 40 μg m-3 within a few kilometres in these areas. The interpretation of the measurements was supported by calculations with OPS, a Lagrangian dispersion model. Model calculations were based on a high-resolution database that included estimates of the ammonia emission of each farm in the area and emissions from surface application of manure at a 250 × 250 m scale. The model underestimated the observed ammonia concentrations by nearly a factor of two over most of the area. This result was attributed to underestimation of the ammonia emission in the models. And the ammonia emissions from field application of manure seem to be seriously underestimated. A detailed analysis of model results and measurements showed that the observed decrease of the ammonia concentration in the study period was partly due to changes in meteorological conditions during the study period and partly due to the reduced amount of manure applied in 1998.