Comparison of fits of Planck and Herschel data in case of different corrections for CO emission. The boxplots show the distribution of field-averaged values of T, β, and 217 GHz excess (relative to fitted modified grey body model, ~5′ resolution). Distributions are plotted dividing each field to pixels below (“N< med”) and above (“N> med”) the median column density. The plots on white background correspond to the default CO correction and the plots on grey background to a CO correction that is twice as high. Each boxplot shows the median parameter value (red horizontal line), the interquartile range (box), and the 10%–90% extent of the distribution (“whiskers”). Each individual field outside the [10, 90%] range is plotted with a plus sign.