Soil’s potential as a sink for atmospheric carbon monoxide

The CO uptake capacity of soils was studied in the field in order to refine previous estimates of the potential of soil as a CO sink. Soils representative of most of the major vegetative regions of North America as well as roadside soils and soils under cultivation were exposed in situ to atmospheres containing initial concentrations of ca. 100 ppm CO in the air. The CO uptake capacities of the soils ranged from 7.6 to 115 mg CO/h/m², with the tropical soils showing the greatest activity and the desert soils the least. Soils under cultivation were consistently less active than the same soils nearby under natural vegetation. Laboratory investigations indicate that the differences were probably not due to agricultural chemicals but rather to a lack of organic matter in the tilled soils. Roadside soils were consistently higher in CO uptake capacity than similar soils in remote regions. Laboratory studies support the idea that this increased rate was due to the constant exposure of roadside soils to high levels of CO. Data for the field studies was corrected for the influence of environmental variables based on laboratory studies and the potential capacity of the soils of the conterminous United States was estimated to be an uptake of 505 million tons of CO per year. This capacity, more than twice the estimated anthropogenic CO in the U.S. annually, indicates that potentially soil is a major sink for atmospheric CO.