[en] Determination of airborne ammonia started in the early 1980s, as a part of air pollution monitoring of industrial plants. Due to high emissions, the city of Rijeka was one of the most polluted in Croatia in the mid-1980s. Considerable reductions in SO₂ and NO_x emissions led to lower airborne levels of these pollutants in the mid 1990s. In spite of the coke plant closure in 1994, there was only a weak decline in airborne ammonia over the period 1980-2005, with annual means in the range of 12-20 μg m^-3 at urban Site 1 and 6-28 μg m^-3 at suburban Site 2. Similar behaviour has been observed with ammonium in bulk rainwater samples since 1996. Higher and approximately equal deposition of nitrogen as ammonium (N-NH₄⁺) were obtained for the urban Site 1 and the mountainous Site 4, but with different causative facts. Ammonium's contribution to total nitrogen (NO₃^- + NH₄⁺) deposition is approximately two thirds, even for a remote Site 3. - Airborne ammonia and ammonium for unknown reasons do not follow the reduction in emission levels