Analysis of wintertime NO₂ pollution in the Tokyo Metropolitan area

The high concentration of NO₂ in the Tokyo Metropolitan area was investigated by means of air quality monitoring station data analysis and two numerical models: a photochemical box model and a photochemical grid model. Based on monitoring data, the typical variation with time of NO, NO₂ and O₃ for days with high NO₂ concentrations is presented. The application of the photochemical box and photochemical grid models successfully reproduced these variations when using typical emission intensities for NO(x) and NMHC from the Tokyo downtown area. Model results revealed that the high concentrations of NO₂ in winter (exceeding the Japan environmental quality standard) mainly result from photochemical oxidation of NO to NO₂.