Three years of continuous measurements of atmospheric ammonia concentrations over a forest stand at the Höglwald site in southern Bavaria

Abstract

Over a period of 3 years (1995 – 1997), atmospheric ammonia (NH3) concentrations were measured 3 m above a spruce stand using a continuous-flow annular denuder at the Hoglwald site near Munich, Bavaria. The annual average ammonia concentration was between 2.2 and 2.9 μg NH3 m−3. The highest hourly average values occurred at the end of each year. In December 1995 the peak value was achieved with 183 μg NH3 m−3. More than 50% of the hourly average means of the ammonia concentration were lower than 2 μg NH3 m−3 and only fewer than 5% of the hourly average concentrations higher than 10 μg NH3 m−3. The ammonia concentration course indicated a pronounced diurnal variation, with higher concentrations in the late morning and lower concentrations during the night. Often a sudden increase of the ammonia concentration was detected in the early morning with first sun exposure of the spruce crown and sinking humidity, indicating a reemission of ammonia from the canopy to the atmosphere.