Quantum yields for NO3 production ill the photolysis of BrONO2 and N2O5 were measured at 248, 308, and 352.5 nm. The measured values for BrONO2 were found to be independent of pressure over the range 150-600 Torr and bath gas (N-2 or O-2) and are 0.28 +/- 0.09, 1.01 +/- 0.35, and 0.92 +/- 0.43 at 248, 308, and 352.5 nm, respectively. Quantum yields of Br and BrO in the photolysis of BrONO2 were also estimated. The measured values for NO3 production in the photolysis of N2O5 were 0.64 +/- 0.10, 0.96 +/- 0.15, and 1.03 +/- 0.15 at 248, 308, and 352.5 nm, respectively. Rate coefficients for the reactions Br + BrONO2 --> Br-2 + NO3 (18) and Cl + BrONO2 --> ClBr + NO3 (19) were measured at 298 K to be k(18) = (6.7 +/- 0.7) x 10(-11) cm(3) molecule(-1) s(-1) and k(19) = (1.27 +/- 0.16) x 10(-10) cm(3) molecule(-1) s(-1). The NO3 product yields for reactions 18 and 19 were measured to be 0.88 +/- 0.08 and 1.04 +/- 0.24, respectively. The absorption cross sections for N2O5 between 208 and 398 nm are also reported. All quoted uncertainties are 2 sigma and include estimated systematic errors, On the basis of the measured quantum yields of NO3, the atmospheric photolysis rate of BrONO2 is discussed.