This paper presents a new unified physics-based framework for describing non-equilibrium thermochemistry and radiative heating in CO2 flows. The use of the coarse grain approach, which involves grouping internal states together into macroscopic bins, allows a dramatic reduction in computational costs while retaining key information from the full state-to-state model. The accuracy of the current model reduction method is further improved by utilizing state-specific kinetics to draw out an optimal strategy for dividing states into bins. In similar fashion, an efficient spectral model is developed from existing comprehensive state-specific radiation databases. This approach combined with finite-volume based discretization for radiative transfer equations allows on-the-fly radiation calculations and a two-way coupling with an unsteady flowfield. The new simulation framework is used to analyze flow dynamics and the radiation field during atmospheric entry for the Mars 2020 mission. Predictions for the forebody region are largely similar for both the reduced-order state-to-state and conventional multi-temperature models. However, the two sets of simulations yield significantly different estimates for the CO2 vibrational state distribution and infrared radiation in the backshell region, especially near the shoulder and along the rear stagnation line.