Publisher Summary This chapter discusses the monitoring and simulation. There are air quality standards for five air pollutants in Japan—that is, sulfur dioxide (SO2), carbon monoxide (CO), suspended particulate matter (SPM), photochemical oxidants (Ox), and nitrogen dioxide (NO2). The measurement methods for these pollutants are discussed in the chapter. The measurement methods for nitric oxide (NO) and non-methane hydrocarbons (NMHC) are also described. A passive monitor can measure air pollutant concentrations without a pump, and can provide simultaneous pollution measurements at many locations. The main difference between passive and active (continuous) monitors is the means by which pollutants are transferred from the atmosphere to the collecting material. Air quality control requires a lot of money, labor, and significant technical development. A theoretical explanation of a dispersion model and the categorization of meteorological and source mission conditions are described in the chapter. Air pollutants found in the atmosphere are discharged from a variety of different sources. These include natural processes and human activities. The contributions to air pollution from these sources are placed in two categories: stationary sources and mobile sources. Emissions produced by human activities are the principal contributors to pollution in urban and suburban areas.