INTRODUCTION The increasing concern over the current high rate of carbon monoxide emission into the atmosphere -- at least partially from automobile exhaust - has stimulated a search for the natural processes that are effective in removing CO from the atmosphere. In the absence of such processes@ an accumulation of CO clearly should occur. A current estimate for the yearly global CO emission from anthropogenic sources rate is 200 million tons@ corresponding to an atmospheric CO concentration increase of 0.05 ppm per year unless a portion of the carbon monoxide is scavenged. A variety of measurements performed over the past 20 years at locations remote from direct urban pollution have shown considerable short-time fluctuations of CO concentrations@ but the average concentration levels seems to have remained essentially constant (see Table 1). Thus@ it appears that one or more atmospheric CO removal processes are operative. This report presents results from laboratory and theoretical investigations directed at identifying chemical processes by which CO is oxidized and removed from the atmosphere. Three aspects are discussed: (a) the photochemical CO oxidation in the stratosphere; (b) reaction of CO with ozone in the troposphere; and (c) CO removal by oxidation In the hydrosphere. In Section II the mechanism of stratospheric CO removal is considered@ and its significance as an atmospheric CO sink is discussed. Section III gives an account of a laboratory investigation of the reaction between CO and ozone. Section IV describes an exploratory experimental study of CO oxidation in aqueous solutions. Finally@ in Section V@ a summary is given of the conclusions drawn from these investigations with regard to atmospheric CO removal processes.