Dichlorvos [2,2-dichlorovinyl dimethyl phosphate, (CH3O)(2)P(O)OCH=CCl2] is a relatively volatile in-use insecticide. Rate constants for its reaction with OH radicals have been measured over the temperature range 296-348 K and atmospheric pressure of air using a relative rate method. The rate expression obtained was 3.53 x 10(-13) e(1367 +/- 239)/T cm(3) molecule(-1) s(-1), with a 298 K rate constant of (3.5 +/- 0.7) x 10(-11) cm(3) molecule(-1) s(-1), where the error in the 298 K rate constant is the estimated overall uncertainty. In addition, rate constants for the reactions of NO3 radicals and O-3 with dichlorvos, of (2.5 +/- 0.5) x 10(-13) cm(3) molecule(-1) s(-1) and (1.7 +/- 1.0) x 10(-19) cm(3) molecule(-1) s(-1), respectively, were measured at 296 +/- 2 K. Products of the OH and NO3 radical-initiated reactions were investigated using in situ atmospheric pressure ionization mass spectrometry (API-MS) and (OH radical reaction only) in situ Fourier transform infrared (FT-IR) spectroscopy. For the OH radical reaction, the major initial products were CO, phosgene [C(O)Cl-2] and dimethyl phosphate [(CH3O)(2)P(O)OH], with equal (to within +/- 10%) formation yields of CO and C(O)Cl-2. The API-MS analyses were consistent with formation of (CH3O)(2)P(O)OH from both the OH and NO3 radical-initiated reactions. In the atmosphere, the dominant chemical loss processes for dichlorvos will be daytime reaction with OH radicals and nighttime reaction with NO3 radicals, with an estimated lifetime of a few hours.