The evaporation and degradation of VX (O-ethyl S-[2-N,N-(diisopropylamino)ethyl] methylphosphonothioate) on silica sand and borosilicate glass were measured using vapor analysis and 31 P solid state magic angle spinning nuclear magnetic resonance (SSMAS NMR) spectroscopy. 31 P SSMAS NMR studies of VX degradation on crushed glass, air-dried sand, and oven-dried sand at a variety of temperatures showed that the final product was nontoxic ethyl methylphosphonic acid (EMPA), produced via the toxic diethyl dimethylpyrophosphonate intermediate. The reaction exhibited a lag time that depended upon the quantity of water and EMPA that were present in the initial sample of VX and was autocatalytic; EMPA was both the catalyst and product for the degradation of VX. 31 P SSMAS NMR studies of VX on moist sand at a variety of temperatures showed that the final product was nontoxic EMPA; observed intermediates were protonated VX, O-ethyl methylphosphonothioic acid, and toxic EA-2192 (S-[2-N,N-(diisopropylamino)ethyl methylphosphonothioic acid). The VX degradation mechanism differed on the moist and dry surfaces; the activation energies were 80 kJ/mol on moist sand and ∼46 kJ/mol on glass, air-dried, and oven-dried sand. The VX degradation rate was 5 to 9 times slower on moist sand than on air-dried sand. Analysis of the vapor emitted showed that the maximum vapor concentration coincided with the maximum surface area of the droplets, which was at ∼300 min. After four days, no further change in the concentration of vapor emitted was detected; approximately 9% of the incident VX drop on sand and ∼60% of the incident VX drop on glass had been recovered as VX vapor.