Simultaneous Monitoring of Nitrogen Dioxide and Aerosol Concentrations with Dual Path Differential Optical Absorption Spectroscopy

Abstract

Differential optical absorption spectroscopy (DOAS) is a useful technique for measuring nitrogen dioxide (NO 2) and aerosol, the most important species in urban environmental pollution. This paper reports on the results of our dual path DOAS measurements recently conducted in Chiba City, Japan, using xenon flashlights equipped on tall constructions as aviation obstruction lights. Because of the proximity of the southern DOAS path to an industrial area, it is found that the level of air pollution generally increases with the dominance of westerly winds, from the plausible source area to the observation light path. This situation is consistent with the result of wind lidar measurement covering a sector of ±28˚ with the observation range of approximately 2.8 km. In spite of the fact that the two DOAS paths, having path lengths of 5.5 and 3.5 km each, are located in separated regions of Chiba City, the observed temporal behavior was similar for both nitrogen dioxide and aerosol, though the southern path tends to exhibit slightly higher pollution levels than the northern counterpart. Additionally it is confirmed that size information of aerosol particles can be derived from the DOAS data through the analysis of the wavelength dependence of the aerosol optical thickness, which shows fairly good correlation with the mass ratio between PM2.5 and suspended particulate matter (SPM) obtained from the in-situ sampling station measurement. Thus, the DOAS approach can also be utilized for obtaining information on PM2.5 that is considered to be more harmful to human health than SPM. H. Saito et al.

Near-infrared open-path measurement of CO_2 concentration in the urban atmosphere

“…Visible or near ultraviolet spectral regions have usually been exploited for conventional DOAS measurements of pollutant gases [11][12][13][14][15]. In contrast, the present Letter describes the application of near-infrared (NIR) spectroscopy for the DOAS-type open path measurement of CO 2 concentration in an urban environment.…”

“…The data analysis procedure is similar to the case of standard DOAS analysis [11][12][13]. Only the outline of the derivation process is described here.…”