Air samples were collected during the test and southbound flight (from Tokyo, Japan to Biak, Indonesia) of International Strato/Tropospheric Air Chemistry I in March 1989 (INSTAC-I). The air samples collected at 4 - 5 km height were subjected to CH4 and CO2 measurement at first, and then CO2 was extracted to measure the carbon isotopic ratio. The concentration of CO2 (ppm, molefraction in dry air) was high over and near the Japan Islands, and shows a little hump around 13°N. The relationship between carbon isotopic ratio and concentration of atmospheric CO2 shows that the high concentration over and near the Japan Islands and a hump around 13°N are caused by the CO2 released by the fossil fuel consumption and/or land plants respiration. The concentration of CH4 (ppm, mole fraction in dry air) was linearly proportional to that of CO2, which suggests a fairly constant ratio between CH4 flux and CO2 flux south of 35°N.
During the INSTAC-I flight campaign in March 1989, 21 air samples were collected and 8 light nonmethane hydrocarbons were measured with an FID-gas chromatograph. The mean concentrations of the hydrocarbons measured were 1.30 ppb (ethane), 0.372 ppb (propane), 0.175 ppb (n-butane), 0.075 ppb (iso-butane), 0.139 ppb (n-pentane), 0.039 ppb (iso-pentane), 0.006 ppb (neo-pentane), and 0.179 ppb (acetylene). All hydrocarbons showed a slight tendency to increase over the tropics. No marked difference was recognized between the samples obtained during the southbound and northbound flights. The sum of relative reactivities of these light hydrocarbons to methane was estimated to be about 26% of methane, which signifies that the effect of light hydrocarbons on atmospheric chemistry in the unpolluted troposphere can not be ignored.
Mixing ratio of nitric oxide (NO) and ozone were measured on board an aircraft over the western Pacific ocean between 7 and 10 th of March, 1989. The latitude range covered was from 35°N to 1°S. NO mixing ratio at 4.5 km varied between 10 and 45 pptv at latitudes between 32 and 15°N and the average NO mixing ratio was about 20 pptv. A peak in NO mixing ratio reaching 45 pptv was encountered near 20°N during both southbound and northbound flights. The average NO mixing ratio at latitudes between 10°N and the equator was about 10 pptv. The latitudinal variation in the ozone mixing ratio was basically similar to that of NO, suggesting larger sources of NO and ozone at mid-latitudes than at lower latitudes.
During the INSTAC-I flight campaign, aerosol number-size distribution was measured in the middle troposphere at 4 - 5 km altitude from 0°N to 34°N by using an optical counter. Aerosol particles were also collected for electron microscopic examinations. Two features of spatial distribution of aerosols were observed over the tropical areas. Sulfuric acid was detected in the particles with a wide size range where the concentrations showed uniform spatial distribution with low values. On the other hand, high aerosol concentrations in which sea-salt particles were dominant instead of sulfuric acid were observed intermittently with space and found to be associated with the existence of convective clouds. The upward transport of sea-salt particles through convective clouds is considered to be responsible for high particle concentrations in the middle tropical troposphere. This suggests that the vertical transport of sea-salt particles would influence the microphysical properties of clouds in the middle and upper troposphere.