Ozone: The ozone monitor was based on the UV absorption method (Model 49, Thermo Electron) with a single illuminant and the double beam dual cell method. This monitor was modified into a 4-second switchover high-speed response type. Both pressure and temperature were automatically corrected. Detection limit was 2 ppb. The ozone monitor was calibrated using an ozone calibrator (Model 49PS, Thermo Electron) owned by NIES as the standard.

Nitrogen Oxides: A nitrogen oxide analyzer based on the NO₂ chemiluminescence method, which itself is based on the reaction of NO + O₃ -> NO₂*, was modified for use in aircraft observations. The main modifications were the introduction of the sample air intake method (800 SCCM) using a mass flowmeter and a method to generate ozone for reaction using pure oxygen, as well as reduction of the pressures of the reactor (absolute pressure of 43-39 Torr) to improve the efficacy of chemiluminescence. A metallic molybdenum reducing agent (with a reaction temperature of 320° C) supported on a carrier was used to convert NOx to NO. Contamination by background emissions was eliminated by an automatic switching of the zero emission mode that passes through the front end reactor (the measurement time was 30 seconds for each cycle, which consisted of NO, NOx and zero measurements). Integration was conducted for two minutes to average the data. Under these conditions, the detection limit of nitrogen oxides was 25 pptv (S/N = 1). It must be noted that the values obtained during the first hour after the commencement of each flight were smaller than the other values by about 5% - 15% due to the insufficient cooling of the photomultiplier (based on the thermoelectric cooling method). Accordingly, the data obtained during this hour had errors of ± 15%.

The analyzer was calibrated by using a commercial NO standard gas diluted by nitrogen. The measurement error during the observations was about 5% or less except during the one hour immediately after the commencement of each flight.

Sulfur Dioxide: Analysis was conducted continuously using an automatic analyzer (Model 43S, produced by Thermo Electron) which is based on the UV pulse fluorescence analysis method. Nevertheless, in this fiscal year, a problem occurred with the control of the sample flow velocity of the measurement device, and the sample flow velocity varied depending on altitude (air pressure). Since this reduced the reliability of the absolute values of the measured data, the flow velocity was corrected by checking the pressure and the sample flow velocity during the observation flight. In addition, using the data of SO₂ concentrations measured based on the diffusion scrubber method by a group from Keio University, correction was conducted to average the observation data obtained by the continuous measurement device mentioned above. During this time, a diffusion scrubber conducted sampling to coincide with the SO₂ concentrations obtained by the diffusion scrubber method.