The thermophysical properties of arc plasma provide reliable micro-theoretical foundations and parameter inputs for the numerical simulation of the air arc discharge process. Based on the assumption of the local thermodynamic equilibrium, the computation of transport properties including electron diffusion coefficient, viscosity, thermal conductivity and electrical conductivity is performed by using the Chapman-Enskog method and expanding the sonine polynomial up to the third-order approximation (second-order for viscosity) in a pressure (0.120 atm) and temperature range (30040000 K) conditions which satisfy most thermal plasma modelling requirements. The most recent data on potential interactions and elastic differential cross sections for interacting particles are utilized to determine the collision integrals, resulting in more accurate and reliable values of transport properties than those given in the previous literature.