The hypersonic, non-equilibrium thermochemistry flow over a cylinder was modeled using direct simulation Monte Carlo (DSMC) method to study Nitric Oxide (NO) ultraviolet (UV) emissions. The main focus of this work was to understand the effect of the amount of molecular oxygen in the free stream flow and different thermochemical models on NO UV emissions. A collisional radiative model was constructed and using this model populations of the electronically excited states are computed to be used in emission spectra calculations. The results showed that as the molecular oxygen mole fraction in the free stream flow changes integrated intensity profiles for the NO emission spectra differ drastically. It was also shown that these integrated intensity profiles are sensitive to the non-equilibrium dissociation modeling and the reaction rate constants used in DSMC simulations. It was concluded that to test the thermochemical models direct comparisons with the flowfields are necessary which can only be done by comparing results with spectral measurements taken at ground test facilities.