The analysis of total column spectroscopic CO observations over Russia revealed an upward linear trend between 1970 and 1995 with a rate of about 1.0 ppbv/year or 0.96%/year. A similar trend was reported earlier for the CO total column over Switzerland between 1950 and 1987. This rate is almost 3 times higher, than the rate of CO increase between 1920 and 1950, obtained from ice core data. Main disturbances of CO tropospheric concentration coincided with vast wildfires in the central Russia in 1972 and volcanic eruptions. Stratospheric volcanic aerosol probably influence the concentration of tropospheric OH radicals, which destroy CO molecules. The aerosol scatters photochemically active UV radiation and, in the same time, triggers the stratospheric ozone photochemical destruction. Diminished total column ozone UV absorption can offset the increase of UV scattering due to additional aerosol. Studying these processes is important for a prediction of further CO and OH long-term variations in the global atmosphere.¿ 1997 American Geophysical Union