Laser-induced fluorescence spectroscopy via excitation of the A(2)Pi(3/2) <- X-2 Pi(3/2) (2,0) band at 445 nm was used to monitor IO in the presence of NO2 following its generation in the reactions O(P-3) + CF3I and O(P-3) + I-2. Both photolysis of O-3 ( 248 nm) and NO2 ( 351 nm) were used to initiate the production of IO. The rate coefficients for the termolecular reaction IO + NO2 + M -> IONO2 + M were measured in air, N-2, and O-2 over the range P = 18-760 Torr, covering typical tropospheric conditions, and were found to be in the falloff region. No dependence of k(1) upon bath gas identity was observed, and in general, the results are in good agreement with recent determinations. Using a Troe broadening factor of F-B = 0.4, the falloff parameters k(0)(1) (9.5 +/- 1.6) x 10(-31) cm(6) molecule(-2) s(-1) and k(infinity)(1) (1.7 +/- 0.3) x 10(-11) cm(3) molecule(-1) s(-1) were determined at 294 K. The temporal profile of IO at elevated temperatures was used to investigate the thermal stability of the product, IONO2, but no evidence was observed for the regeneration of IO, consistent with recent calculations for the IO-NO2 bond strength being similar to 100 kJ mol(-1). Previous modeling studies of iodine chemistry in the marine boundary layer that utilize values of k( 1) measured in N-2 are hence validated by these results conducted in air. The rate coefficient for the reaction O(P-3) + NO2 -> O-2 + NO at 294 K and in 100 Torr of air was determined to be k(2) ( 9.3 (0.9) x 10(-12) cm(3) molecule(-1) s(-1), in good agreement with recommended values. All uncertainties are quoted at the 95% confidence limit.