Retrievals of AIRS CO2 from the 4 micron region have been shown to have peak sensitivity around 500 hPa, significantly lower than the standard AIRS CO2 product which peaks near 200 hPa in the tropics. This channel therefore has the potential to add to our knowledge of the distribution of tropospheric CO2 and improve estimates of CO2 source/sinks through flux inversion. In this work we have assimilated clear sky retrievals from the 4 micron channel into the GEOS5 system for a 2 year period starting in January 2005. Comparisons with ground and aircraft based in situ data show significant improvements to CO2 estimates at all levels of the troposphere, and particularly in the lower troposphere. We are also assimilating the 2 AIRS CO2 products simultaneously, and will show some initial results from this ongoing work.