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.