Urban air pollution monitoring using differential optical absorption spectroscopy (DOAS) and wind lidar

The technique of differential optical absorption spectroscopy (DOAS) is applied to monitor concentrations of nitrogen dioxide (NO₂) and aerosol, the major pollutants in the urban atmosphere. Two DOAS paths with optical distances of a few kilometers have been set up in the Chiba city area. The spectra of visible radiation emitted from xenon flashlights installed on tall constructions are analyzed in comparison with the laboratory spectrum of NO₂. The intensity stability of the light sources enables the retrieval of aerosol extinction along the paths. It is found that the temporal behavior of both pollutants is similar to those observed at nearby ground sampling stations, though the effect of difference in the observation height often appears. Wind Doppler lidar measurement has also been undertaken from an observation site near an industrial complex along the Tokyo Bay, suggesting the influence of wind direction on the pollutant concentrations observed in the region.