CO₂ vertical column density maps of the leading (left) and trailing (right) hemispheres. They were deduced from the line-of-sight column density maps, by multiplying them by the cosine of the angle between local zenith and line of sight directions. For the leading hemisphere, the central contour for the north excess is at about 72°W (12.6 h local time), 45°N. Trailing data were smoothed using a 3×3 boxcar filter.