| Research Abstract |
Tropospheric column amounts and mixing ratios of carbon monoxide (CO), ethane (C_2H_6), acetylene (C_2H_2), and hydrogen cyanide (HCN) were retrieved from ground-based infrared solar spectra. The spectra were recorded with high spectral resolution Fourier Transform Infrared (FTIR) spectrometers at Moshiri (44.4°N) and Rikubetsu (43.5°N) in northern.
The retrievals show significant seasonal variations in the tropospheric content of the four molecules over northern Japan with maxima in winter-spring (February-April) for CO, C_2H_6 and C_2H_2 and in summer (May-July) for HCN.Simultaneous enhancements of the tropospheric concentration of the four molecules were occasionally observed during the observational period, possibly due to the same sources. Good correlations among the tropospheric amounts of CO, C_2H_6, and C_2H_2 indicated that they had similar sources and underwent similar processes of dilution. Trajectory calculations and global fire maps revealed that emissions of biomass burning on the Asian continent were transported eastward to northern Japan. Decreasing trends in tropospheric CO, C_2H_6, and C_2H_2 from May 1995 to June 2000 were found to be (-2.10±0.30), (-2.53±0.30), and (-3.99±0.57)%yr, respectively, while the trend of (-0.93±0.49)%/yr in HCN was not significant. Since stratospheric O_3 absorbs the solar UV radiation, the depletion of global stratospheric O_3 since mid-1980s resulted in an increase of the solar UV radiation on the earth surface. It is appear that the observed negative trends in tropospheric CO, C_2H_6, and C_2H_2 over northern Japan should be due to the increase in the solar UV radiation through the photochemical reactions with OH.In addition, reduced emissions of these gases from biomass burning and anthropogenic sources in the past decade would be another reason for the decreasing trends in troposphericCO, C_2H_6, and C_2H_2 observed in northern Japan from May 1995 to June 2000.
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