Ammonia plays an important role in atmospheric chemistry and acid deposition. The pollution problem caused by ammonia has to be considered on an international basis as it is being transported over long distances. The importance of that acid deposition was not widely appreciated few years ago. More intensive livestock production and fertilizers uses have increased the ammonia emissions in Europe which come dominantly from agricultural activities. The fate of ammonia in the atmosphere is complicated. Modeling have been used to study the transport of ammonia and its interaction with other acidic compounds (H, Cl, HNO3 AND H2SO4).