Measurements of Ozone, Nitrogen Dioxide and Sulfur Dioxide by an Open-Path Differential Optical Absorption Spectrometer in Higashi-Hiroshima, Hiroshima Prefecture

MATSUDA Toshihide, HIRAKAWA Tsuyoshi, SAKUGAWA Hiroshi

doi:10.2116/bunsekikagaku.54.325

A field-based intercomparison study of a commercial open-path differential optical absorption spectrometer (DOAS) and conventional point monitoring techniques for ozone (O₃), nitrogen dioxide (NO₂) and sulfur dioxide (SO₂) was conducted from August to September, 1999, in Higashi-Hiroshima, Hiroshima prefecture. O₃, NO₂ and SO₂ were measured every 10 minutes by an ultraviolet-ray absorption method, a chemiluminescence method, and a fluorescence method, respectively, while all of these three gases were simultaneously monitored every 20 minutes by the DOAS system (DOAS 2000, Thermo Electron Nippon Co. Ltd., Japan). Very good correlations were found for O₃ (r² = 0.96) and SO₂ (r² = 0.93), while a slightly lower correlation existed for NO₂ (r² = 0.80). The average concentrations of these gases monitored by the DOAS system were 1.1, 1.2, 1.6 times higher than those measured by conventional point monitors, respectively. Vehicle emissions from the surrounding area of the monitoring site caused atmospheric inhomogeneities, which were involved in the lower correlation for NO₂ by causing differences in the analytical values of the two methods. A much higher slope of SO₂ (1.6) was considered to result from the use of an inaccurate standard spectrum in DOAS analysis, which was prepared from 100 ppm level reference gas. Precipitation (0.5 ~ 35.0 mm h⁻¹) and the relative humidity (25.6 ~ 99.9%) didn’t affect the DOAS measurements. Fog interrupted the DOAS measurements of all compounds in during several periods; it occurred when the relative humidity was kept over 99% for a few hours from midnight to morning. The mobile emitting source and the meteorological situations should be considered when monitoring is carried out by DOAS.<br>

Measurements of Ozone, Nitrogen Dioxide and Sulfur Dioxide by an Open-Path Differential Optical Absorption Spectrometer in Higashi-Hiroshima, Hiroshima Prefecture

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