In this review article for the academic award, the outline of our atmospheric observational research is presented. The acid rain problem, which was my graduation thesis, is a comprehensive science related to the atmosphere, biosphere, hydrosphere, and pedosphere. The study of acid rain is generally said to be over, but I have learned the importance of totally understanding air pollutants in the gas/particulate/aqueous phase, continuing the observation from a long-term perspective, and the viewpoint of water/material circulation through research activities on acid rain. The contents are divided into five parts as follows. (1) observation of the atmospheric chemistry in the free troposphere and in the mountains, (2) the mechanism of the enhanced dissolution of toxic air pollutants into the atmospheric water, (3) the origin/dynamics/roles of atmospheric surfactants, (4) atmosphere-forest interaction, and (5) linkage between atmospheric environment and disasters. The establishment of earth health management has a long way to go, but I would like to continue studying atmospheric observation research.

The dry deposition of atmospheric ammonia (NH₃) volatilized from feedlots, one of major loads of nitrogen into the basin, has been rarely observed at the tree canopies close to the feedlot in Ibaraki, Japan. We made multi-point annual observations of the NH₃ concentration using passive samplers within and surrounding the cattle feedlot in Ibaraki. The throughfall and wet deposition of ammonium-nitrogen (NH₄⁺-N) was also measured by bulk samplers under Japanese cypress trees near the feedlot. The annual mean NH₃ concentration measured inside the feedlot (322 ppbv) was lower than that expected from the cattle density, suggesting the requirement for monitoring the micrometeorological environment and management processes inside the feedlot. The results also indicated that the local-scale spatial distributions of the NH₃ concentration may be influenced by not only horizontal wind directions but also air temperature and humidity, buildings, and trees. The annual throughfall deposition of NH₄⁺-N (27.5 kgN/ha/yr) was clearly greater than those observed in the Japanese forests in past studies, suggesting the high impact of the dry deposition of NH₃ volatilized from the feedlot. The deposition velocity of NH₃ was estimated to be 3.4±2.5 cm/s, which was the highest range level of literature values for coniferous forests.

The hourly optical black carbon (OBC) concentrations in PM_2.5 were measured in the south (NCIES) and north (Konan) of Nagoya City in Aichi Prefecture, Japan. In the summer, the OBC concentrations were high in the daytime under the sea breeze conditions in NCIES but no strong diurnal variation for the OBC was observed in Konan. The V and Ni in the PM_2.5 also showed high concentrations in the daytime in the NCIES. The source analysis of elemental carbon in the PM_2.5 in NCIES using a chemical transport model (CMAQ) showed dominant contributions from automobile exhausts in the morning and from ship exhausts during the daytime. The simulated daytime OBC concentrations in NCIES were higher than those at Konan, which properly fit the observed data at the sites. According to the results of tracer elements and the model simulation, the high OBC concentration observed in the daytime in the NCIES was caused by contribution from heavy oil combustion around the bay area under the sea breeze conditions.

This study has developed a new ambient pollutant emission inventory for large stationary sources classified by sectors, facilities, and fuel types. It utilizes emission factors and facility fractions derived from records of Research of Air Pollutant Emissions from Stationary Sources. Derived emission factors are consistent with existing studies. Emissions estimated in this study are consistent with emissions reported in Research of Air Pollutant Emissions from Stationary Sources. However, it is necessary to consider changes in emission factors caused by control technology developments in order to represent trends of emissions for past and future years. Vertical emission profiles for facilities have also been developed. Three-dimensional air quality simulations using emissions estimated in this study result in 1 μg/m³ increase and 2 ppb decrease of annual mean PM_2.5 and daily maximum O₃ concentrations, respectively, against simulations using existing emissions.

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.