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.