Abstract

In this report results of the additional monitoring programme on NH3 are reported. The aim of this project was to evaluate long range transport model (TREND) results on NH3 concentrations in high density emission areas. For this evaluation, continuous ammonia concentrations were measured during one year at two locations in the Netherlands (Vredepeel and Lunteren). Furthermore, the representativeness of these fixed point measurements was investigated using mobile measurements and a short term/short range transport model for NH3 (SLAM). The measuring strategy developed for this research provides a good tool for estimating the representativeness of a single point measurement for a larger area surrounding the fixed-point. The results using the SLAM model agree reasonably well with measured concentrations in time and space, provided that data are selected for wind speed > 1.5 m.s-1. In comparing model results with measurements the greatest uncertainty results from emission estimates and temporal variation in emissions. The uncertainty in the annual average concentrations obtained at the fixed-point is estimated at 20-25%. The Vredepeel fixed-point is representative within 10% in comparison with the surrounding 5 x 5 km area. Due to a lack of measurements at the Lunteren fixed-point no final statement can be made for this area, although measurements and SLAM calculations show 30-40% higher concentrations in comparison with the 5 x 5 km grid. TREND calculations show 30-40% variation in using different meteorological data (national or local), emission estimates and temporal variations in emission. The final conclusion of this research is that there is no significant difference between TREND results and yearly average measured concentrations for high ammonia emission areas. Hereby the measured concentration should be evaluated on representativeness for a surrounding 5 x 5 km area and local meteorology and the best guess on emissions should be used as input for TREND calculations.