The kinetics of the reactions of PO with O2 and PO2 with O3 were studied at temperatures ranging from ∼190 to 340 K, using a pulsed laser photolysis-laser induced fluorescence technique. For the reaction of PO + O2, there is evidence of both a two- and three-body exit channel, producing PO2 + O and PO3, respectively. Potential energy surfaces of both the PO + O2 and PO2 + O3 systems were calculated using electronic structure theory and combined with RRKM calculations to explain the observed pressure and temperature dependences. For PO + O2, at pressures typical of a planetary upper atmosphere where meteoric ablation of P will occur, the reaction is effectively pressure independent with a yield of PO2 + O of >99%; the rate coefficient can be expressed by log10(k, 120-500 K, cm3 molecule-1 s-1) = -13.915 + 2.470 log10(T) - 0.5020(log10(T))2, with an uncertainty of ±10% over the experimental temperature range (191-339 K). With increasing pressure, the yield of PO3 increases, reaching ∼90% at a pressure of 1 atm and T = 300 K. For PO2 + O3, k(188-339 K) = 3.7 × 10-11 exp(-1131/T) cm3 molecule-1 s-1, with an uncertainty of ±26% over the stated temperature range. Laser-induced fluorescence spectra of PO over the wavelength range 245-248 nm were collected and simulated using pgopher to obtain new spectroscopic constants for the ground and v = 1 vibrational levels of the X2Π and A2Σ+ states of PO.