On the possible increase of the atmospheric methane and carbon monoxide concentrations during the last decade

Various published measurements of the background concentrations of ground level atmospheric methane suggest an increase from ∼1.6 ppm to ∼1.7 ppm over the past decade. To supplement these analyses, we have analyzed ten years of continuous data from three urban/suburban sites and find that the annual minima in the monthly midmeans of daily minima follow this suggested pattern in both direction and magnitude. A similar but less well-characterized result is obtained for carbon monoxide as well.