Rate constants for the reactions of OH radicals with isopropl methyl methylphosphonate [(CH3)(2)CHOP(O)(CH3)OCH3; IMMP] and dimethyl N,N-dimethylphosphoroamide [(CH3O)(2)P(O)N(CH3)(2); DMDMPA] have been measured over the temperature range 283-350 K and atmospheric pressure of air using a relative rate method. The rate expressions obtained were 2.72 x 10(-13) e((1642 +/- 144)/T) cm(3) molecule(-1) s(-1) (6.72 x 10(-11) cm(3) molecule(-1) s(-1) at 298 K) for OH + IMMP and 6.05 x 10(-13) e((1185 +/- 144)/T) cm(3) molecule(-1) s(-1) (3.23 x 10(-11) cm(3) molecule(-1) s(-1) at 298 K) for OH + DMDMPA. In addition, rate constants for the reactions of NO3 radicals and O-3 with IMMP were measured at 296 +/- 2 K, of (4.8 +/- 2.1) x 10(-16) and <7 x 10(-20) cm(3) molecule(-1) s(-1), respectively. Products of the OH radical-initiated reactions were investigated using gas chromatography, in situ atmospheric pressure ionization mass spectrometry (API-MS), and in situ Fourier transform infrared (FT-IR) spectroscopy. For the OH + IMMP reaction, the major initial products appear to be CH3OP(O)(CH3)OC(O)CH3 + (CH3)-C-center dot, with subsequent reactions of the methyl radical in the presence of NOx leading to HCHO, CH3ONO, and CH3ONO2. For the OH + DMDMPA reaction, (CH3O)(2)P(O)N(CH3)CHO was observed as a Significant product. Possible reaction mechanisms are discussed.