Smog chamber/FTIR techniques were used to study the Cl atom initiated oxidation of 4:2 fluorotelomer alcohol (C4F9CH2CH2OH, 4:2 FTOH) in the presence of NOx in 700 Torr of N-2/O-2 diluent at 296 K. Chemical activation effects play an important role in the atmospheric chemistry of the peroxy, and possibly the alkoxy, radicals derived from 4:2 FTOH. Cl atoms react with C4F9CH2CH2OH to give C4F9CH2C.HOH radicals which add O-2 to give chemically activated alpha-hydroxyperoxy radicals, [C4F9CH2C(OO.)HOH]*. In 700 Torr of N-2/ O-2 at 296 K, approximately 50% of the [C4F9CH2C(OO.)HOH]* radicals decompose ``promptly'' to give HO2 radicals and C4F9CH2CHO, the remaining [C4F9CH2C(OO.)HOH]* radicals undergo collisional deactivation to give thermalized peroxy radicals, C4F9CH2C(OO.)HOH. Decomposition to HO2 and C4F9CH2CHO is the dominant atmospheric fate of the thermalized peroxy radicals. In the presence of excess NO, the thermalized peroxy radicals react to give C4F9CH2C(O-.)HOH radicals which then decompose at a rate >2.5 x 10(6) s(-1) to give HC(O)OH and the alkyl radical C4F9CH2.. The primary products of 4:2 FTOH oxidation in the presence of excess NOx are C4F9CH2CHO, C4F9CHO, and HCOOH. Secondary products include C4F9CH2C(O)O2NO2, C4F9C(O)O2NO2, and COF2. In contrast to experiments conducted in the absence of NOx, there was no evidence (