RESPONSE OF A GRASSLAND ECOSYSTEM TO AIR-POLLUTANTS .3. THE CHEMICAL CLIMATE - VERTICAL FLUX DENSITIES OF GASEOUS SPECIES IN THE ATMOSPHERENEAR THE GROUND

The establishment of element balances for ecosystems presupposes a kno wledge of the amounts of the respective element exchanged between the ecosystem and the atmosphere near the ground by determining their vert ical flux densities. Any adequate approach to calculate flux densities of gaseous species in the atmosphere has to use micrometeorological t echniques. The authors applied the ratiometric method, which is descri bed in detail. Results of flux density calculations for sulfur dioxide , nitrogen dioxide, nitric oxide and ammonia obtained during two years of measurement are discussed with regard to their role in element bal ances. Flux densities and deposition velocities of ozone are interpret ed as functions of meteorological parameters as well as of the biologi cal activity of the canopy. The latter is characterized by the flux de nsity and flux-to-concentration ratio of carbon dioxide.