(at 13000 cm� 1) was varied from 0 to 0.3. The radiance errors using the Radiant/2OS (R-2OS) RT model are an order of magnitude (or more) smaller than errors arising from the use of the scalar model alone. In addition, we perform a linear error analysis study to show that the errors in the retrieved column-averaged dry air mole fraction of CO2 (XCO2) using the R-2OS model are much lower than the ''measurement'' noise and smoothing errors appearing in the inversemodel. Onthe otherhand, weshow thatuseofthe scalar modelalone induces XCO2 errors that could dominate the retrieval error budget.