Trends in Atmospheric Ammonia and Particulate Ammonium Concentrations in Japan

Abstract

To evaluate the contribution of NH₃ (g) gas and NH₄⁺(p) particles to the nitrogen deposition, the Japan Environmental Laboratories Association has observed the concentrations of NH₃ (g) gas and NH₄⁺(p) particles by the filter pack method. Based on the analytical results obtained during the period of fiscal years 2004–2013, we examined the long-term changes in the concentrations of NH₃ (g) gas and NH₄⁺(p) in the ambient air of Japan. The concentration of NH₃ (g) showed a gradual reduction throughout the period for the entire studied area. On the other hand, the concentration of NH₄⁺(p) increased in 2005–2007 in Western Japan. We also estimated the amount of NH₃ emissions in Japan, whose decreased pattern was roughly similar to that for the concentration of NH₃ (g). The increase in NH₄⁺(p) in Western Japan did not correlate with the decrease in the amounts of NH₃ emissions in Japan, however, it was agreed with the concentration of nss-SO₄^2- (p). The discharge reduction of sulfur dioxide which is the precursor of sulfuric acid, in Japan over the past 30 years, and the increased trend of China in 2005–2007, indicate the influence of the transported pollution from the continent.