Evaluation of ammonia fluxes into the free atmosphere over Western Germany

The upward flux densities of gaseous ammonia and particulate ammonium through a layer 400 m above ground were determined by aircraft measurements over a rural area in Western Germany. The flux densities were calculated according to the gradient method. The fluxes amounted to 118 ± 49 µg/m2h NH3-N and 93 ± 47 µg/m2h NH+4-N in summer and to 7 ± 14 µg/m2h NH3-N and 23 ± 34 µg/m2h NH+4-N in winter.When integrated over a year, the sum of these ammonia fluxes can be maintained by NH3 volatilization from domestic animal excrements. The NH3 liberation from mineral fertilizer and natural soils contributes only a small amount to the overall production rate. Most of the NH3 and NH+ 4 diffusing upwards into the middle troposphere will eventually be incorporated in rain. For the conversion of gaseous NH3 to particulate NH+ 4 in the first 400 m of the atmosphere a lower limit for a pseudo first-order reaction rate constant of 1–2 x 10-5 s-1 was deduced from flux density considerations.