Tropospheric column amounts and mixing ratios of CO, C2H6, C2H2, and HCN were retrieved from ground-based infrared solar spectra using a vertical profile retrieval algorithm (SFIT2). 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 Japan from May 1995 to June 2000. 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, C2H6, and C2H2 and in summer (May--July) for HCN. Good correlations between CO, C2H6, and C2H2 indicated that they had similar sources and underwent similar dilution processes. Deviation of HCN relative to its seasonal mean value (ΔHCN) is correlated with the similar deviation of CO (ΔCO), indicating that enhancements of CO and HCN above the mean levels were probably due to the same sources. Linear trends in tropospheric CO, C2H6, and C2H2 from May 1995 to June 2000 (excluding 1998) were (-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 relatively small. Abnormally high tropospheric amounts of the four molecules were recorded in 1998. HCN amounts were found to be much higher than its seasonal mean value throughout 1998 with a 65% maximum increase in August 1998. Significant increases of CO, C2H6, and C2H2 took place in August--October 1998. Trajectory calculations, global fire maps, and satellite smoke images revealed that biomass burning in eastern Siberia from mid-July to early October 1998 was the major cause of the elevated levels in tropospheric CO, C2H6, C2H2, and HCN observed in northern Japan in 1998.