This paper presents a new method to determine the evaporation coefficient of trichloroethylene using a new experimental device called "activity-meter". This device and the associated method have been developed in the Laboratory of Mechanical Engineering of the University of Montpellier 2 (France). The influence of diffusion on the vapor pressure of trichloroethylene and the influence of temperature at the liquid-gas interface were first determined. The results show that diffusion phenomena have no influence on the vapor pressure of trichloroethylene beyond 400 s of experimental time and the temperature is almost constant during experiments. Thus, in order to take into account the effects that are only due to the variation of partial pressure of trichloroethylene at the liquid-gas interface, the time interval used is between 400 s and the time required to reach equilibrium. The influence of pressure and temperature on the evaporation coefficient of pure trichloroethylene in an arid soil was then highlighted. The results show that the evaporation coefficient of trichloroethylene decreases with total vapor pressure but increases with temperature. A comparative study on evaporation coefficients conducted on water, heptane, and trichloroethylene shows that our results are in good agreement with results on volatility.