In order to clarify the mechanism o f photochemical smog in the Tokyo Metropolitan Area, numerical simulation was performed. First, only dispersion was treated, by the use of sulfur dioxide (SO2) and nitrogen oxides (NOx) as inert gas. And then photochemical smog was simulated by the dispersion model thus evaluated, combined with a photochemical reaction model. The simulatio n model was developed in both Lagrangian and Eulerian forms, and case studies were carried out. In the Lagrangian approach (namely, moving parcel method), lateral diffusion was considered by "receptor-oriented method" and Friedlander and Seinfeld (1969) was used as a photochemical reaction model. In the Eulerian approach, calculation scheme MRI-E10 was developed for preventing "artificial diffusion" (see Appendix A), and the reaction model by Eschenroeder and Martinez (1971) and Sugiyama (1974) was utilized. Generally speaking, results for SO2 and NOx were fairly good. Simulation of the photochemical smog, however, was not so satisfactory yet. More information on the emission source (especially of hydrocarbon) in the area is indispensable, and a more practical model of the photochemical reaction in the atmosphere should be developed.
For many purposes it is required to k now the actual range at which an object of some definite area and shape can be recognized. If the proper value can be given to the liminal contrast (=0.02), we can compute the visual range. For this purpose it is necessary to measure the extinction coefficient a and the contrast C of two adjacent surfaces. The main concern is the characteristics of the human eye and the optical parameters of the atmosphere. The visual range can be calculated from the transmittance and the distance of 0.15 km between the projector and the telephoto meter will limit the liminal visual range up to 4-5 km, so that for the longer visual range (10 km or more) it is necessary to investigate not only the transmittance but the reduction rate of contrast between the objects and their backgrounds (by contrast meter and telephoto meter). In this paper the instruments, some experimental results and the method s of the determination of the visual range are described. An ITV camera is now largely used for monitoring the field view and the information can be telemetered through the narrow band telephone line. Usually the camera eye has different characteristics from the human eye. So that it is necessary to investigate the relation between actual view and camera image under different optical conditions by means of the measured value of the visual range.