A relative rate study has been performed on the reactions CH3C(O)O-2(.) + NO2 + M --> CH3C(O)O2NO2 + M (1) and CH3C(O)O-2(.) + NO --> CH3. + CO2 + NO2 (2) in an atmospheric flow system in which the relative yields of CH3C(O)O2NO2 (PAN) have been measured as a function of the ratio of reactants [NO]/[NO2]. Over the temperature range 247-298 K, at a total pressure of similar to 1 atm,the ratio was independent of temperature, k(1)/k(2) = 0.41 +/- 0.03, where the error limits are 2 sigma. The results are discussed with reference to other relative rate measurements of k(1)/k(2) and to absolute measurements of k(1) and k(2). The atmospheric implications of the ratio k(1)/k(2) in relation to PAN are briefly considered.