Studies designed to measure the apparent first order decay of the NO3 radical are reported here: NO3(+M)→NO+O2(+M)(R1). Two techniques were employed: (1) direct absorption measurements of 2> and 3> were made in the visible in a mixture of N2O5 in nitrogen; and (2) NO3 was followed indirectly through measured infrared absorptions of NO2 and N2O5 and calculated from the N2O5 equilibrium relation. Rate data were obtained in experiments over a range of temperatures (313--347 K) and pressures of added N2(5--2000 torr). Rate coefficient data obtained in experiments at PN240 torr show an apparent increase in k1 with PN2, and a negative temperature coefficient which is attributed to a wall-catalyzed decomposition of NO3, presumably to form NO and O2 by the stoichiometry of reaction (R1). Although our observations of the kinetics of reaction (R1) are not only qualitative, they support those of Johnston et al. The occurrence of a first order, homogeneous decomposition of NO3 in the atmosphere can explain most of Noxon's (1983) observations of NO3 scavenging in the troposphere. However, his reported loss of NOx during the nighttime hours requires, in addition, a contribuiton from some other, unidentified reaction pathway. Alternatives for this removal mechanism are discussed in view of our current knowledge. ¿American Geophysical Union 1990