These images were produced by comparing the atmospheric CO2 concentration
arising from simulation of two different fossil fuel carbon dioxide emission 
inventories through the Parameterized Chemistry and Transport Model (PCTM). 
The first inventory is the Vulcan 2002 inventory regridded to the 1x1.25 
degree PCTM grid and integrating those emissions for one full year. The second 
inventory is the Brenket et al., 1998 fossil fuel CO2 emissions inventory 
(http://cdiac.ornl.gov/epubs/ndp/ndp058a/ndp058a.html)
also regridded to the 1x1.25 degree PCTM grid but scaled up at all cells to 
match the 2002 Vulcan US total carbon emissions.

The differences shown in the online images are obtained by subtracting the
outputs obtained from Brenkert et al. emissions from the the Vulcan
emissions at the second layer (850 mb) of the atmosphere from the surface.
The Winter mean is obtained by averaging the results of the months of December, 
January, and February and the Summer mean is obtained by averaging the months 
of June, July, and August, the Annual mean encompasses the entire year.