Abstract
In 2005, the study group organized by the Tokyo Metropolitan Government to plan countermeasures against photochemical oxidants (Ox) estimated the effects of the reduction in the precursors, non-methane hydrocarbons and nitrogen oxides, based on the observed relationship between the precursor and Ox concentrations during 2000–2002. The result, and the logic of the estimate is validated using the monitoring data obtained after those years. At the same time, the question, how much is the recent trend of occurrence of high levels of Ox attributed to the reduction of the precursors, is examined.
The estimate method lacks any procedure to exclude the ettect of year-to-year variations in climate, and needs to incorporate some technique to select sample days satisfying a meteorological standard, an example of which is the “sea breeze days”.
The estimate given in 2005 generally well describes the recent state of high-level Ox over the central region of the Kanto plain, meaning that the situation has been improved due to the reduction of the precursors. However, the northern part of the area still remains at high Ox levels for some structural reason.
