In early winter season, severe air pollution due to suspended particulate matter occurs frequently at South-Kanto Plain. During such episodes observed on November 26 and 27, and December 6 and 7 in 1991, intensive field observations were conducted in order to investigate the behavior and source of atmospheric particulate chlorides. Although very high concentrations of TSP, SPM2.4 (fine particles less than 2.4 μm) and chlorides were observed, very low level of seasalt chlorides were found. Thus, most of the total chlorides in suspended particulate matter were non-seasalt chlorides existing in fine particles less than 2.4 μm collected at Kanda or Urawa. The result of high correlations (significance levels higher than 99%) between [Cl-]nss and [K+] or [Cl-]nss and [Zn] calculated for SPM2.4, shows the evidence that high level of non-seasalt chlorides was the secondary products of HCl emitted from refuse incineration and/or biomass burning under the stagnation with low temperature and high relative humidity of lower layer in early winter.
In order to achieve the simultaneous removal for the reactive gases from ppb to ppm level and fine particles, we investigated on a new removing technique using UV/catalyst and UV/photoelectron charging methods. In this technique, gaseous pollutants are converted to adsorptive gases and fine particles, and then they are adsorbed on the honeycomb-catalyst and/or collected with UV/photoelectron charging method. When this technique was applied to removing sub-ppm levels of reactive gases, NO, NO2 and SO2, the obtained removal efficiencies were nearly 100 %. The particles generated from gaseous species were also removed with UV/photoelectron charging method under the application of a weak electric field and an irradiation of 184.9 nm of UV light. Furthermore, we applied this technique to trace amounts of SO2 (10 ppb in the present study) to discuss the influences of various factors on the secondary particle formation. The optimum conditions in the used reactor were determined and its capability was estimated.
Mixing thin film was prepared on a Nuclepore filter by dual vacuum deposition of barium chloride and nitron in order to detect the mixing states of sulfate and nitrate in individual aerosol particles. The mixing states were identified by the characteristic spots of Liesegang ring and/or needle crystals from SEM (scanning electron microscope) observation of the samples. Applicability was examined using sulfate and/or nitrate particles generated by a nebulizer. It was found that the reactions of sulfate with barium chloride and of nitrate with nitron were promoted and reproducible in ethanol and 2-propanol mixing solvent vapor. The mixing thin film method was applied to detect the mixing states of atmospheric aerosols collected by Andersen samplers at Uji in summer and winter seasons. In winter, internally mixed sulfate-nitrate particles were not detected, while internally mixed particles were found to be a few percent in number concentration to the total particles collected on each stages of the sampler in summer.