The reactions (1) NO3 + Cl = NO2 + ClO and (2) NO3 + HO2 = HNO3 + O2 were studied using a flash photolysis-laser absorption technique. HNO3/HCl mixts. were used as a photolytic source of both NO3 and Cl, and HNO3/H2O2 as the source of NO3 and HO2. The rate coeffs. for (1) were independent of temp., whereas for (2) a slight decrease was obsd. between 298 and 353 K.