Measurement of Volcanic SO<sub>2</sub> Concentration in Miyakejima Using Differential Optical Absorption Spectroscopy (DOAS)

Abstract

Since the volcanic eruption in 2000, continuous monitoring of sulfur dioxide (SO 2) gas has been conducted with in-situ samplers located along the seashore road in Miyakejima, a volcano island around 180 km south of Tokyo. The purpose of these sampling measurements has been to issue warning on the hazardous air pollution to the local residents. Therefore, the resulting data do not provide direct information on pollution levels inside the restricted areas where high concentration of SO 2 still takes place frequently. From the ecological point of view, it is desirable to have pollution data covering wider regions of the island. In this paper we report on our differential optical absorption spectroscopy (DOAS) measurements carried out inside the highly-polluted, restricted areas in Miyakejima in December 2009 and September 2010. The system is based on continuous light emitted from a xenon light sources, while detector setups consisting of a telescope and a compact spectrometer detect the light after passing a nearly horizontal optical path of 460 m-1300 m. By virtue of the portability of the DOAS observation systems, we achieved the measurement of the concentrations inside the restricted districts in the eastern and southwestern parts of the island. The DOAS results in both of these districts revealed the occurrence of pollution of volcanic gas even when no pollution was observed at nearby sampling stations. In addition, simultaneous measurements with two nearly orthogonal DOAS paths were conducted for examining the spatial distribution of the volcanic gas over the spatial range of several hundred meters. The result of this two paths measurement has indicated the importance of orography, in addition to the wind speed and wind direction, in determining the spatial concentration of SO 2 emitted from the volcano crater.

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

“…The measurements employed two independent DOAS paths having optical path lengths of 5.5 and 3.5 km that cover different areas in the central part of Chiba City, located along the eastern coast of the Tokyo Bay. The use of such dual light paths in DOAS has recently been reported for an urban air pollution study in Tokyo [14] as well as for the monitoring of volcanic gas concentration [15]. In addition, the novel aspect of the present paper is the simultaneous measurement using a Doppler wind lidar [22], which can provide more direct information on the wind field as compared with the weather station data.…”

“…It often happens, however, that such point sampled data are affected by local sources, and consequently, they do not always represent air pollution conditions in a wider region [4]. The technique of differential optical absorption spectroscopy (DOAS) is capable of monitoring atmospheric environment along the optical path of several hundred meters to several kilometers [5]- [15]. By utilizing appropriate wavelength range in the visible spectrum, the DOAS technique makes it possible to measure the concentrations of nitric dioxide (NO 2 ) and aerosol, two important species in urban environmental pollution [7] [8].…”

Bistatic LIDAR System for the Characterisation of Aviation-Related Pollutant Column Densities

“…Due the advent of powerful tuneable laser sources, a variety of LIDAR systems have been developed for measuring the column density of various important molecular species, both locally and over extended geographic areas [3][4][5][6][7][8][9]. Optical absorption spectroscopy was also successfully applied to SO 2 concentration measurements [10]. A variety of ground-based, airborne and space borne applications are conceived, including gliders, balloons, parachutes, roving surface vehicles, satellites and interplanetary sondes.…”