For eons, the kinetic theory (KT) of gases has been used to determine the MFP assuming elastic collisions between spherical gas molecules [1]. However, is this so with what we know about molecular shape and force fields today? Having reached a state of maturity now, molecular dynamics (MD) simulations can elucidate the fundamentals of basic gas-phase (aerosol) processes that lead to a) better understanding of natural phenomena and b) accelerating process scale-up [2]. Here the mechanics of gas collisions are elucidated for plain air at room temperature by thoroughly-validated atomistic MD treating O2 and N2 as true diatomic molecules accounting for their shape and force field, for the first time to our knowledge [3]. …..