An instruments has been developed to analyze the size and chemical composition of individual, air-borne particles. The particles are introduced into the vacuum chamber of a time-of-flight mass spectrometer where they are detected and sized using an aerodynamic principle. After sizing, the particles are vaporized by an excimer laser and the resulting ions are analyzed. Experiments have shown that polystyrene particles 1 μm in diameter are not fully vaporized by the laser pulse. The instrument has been characterized and some examples of measurements on ambient and artificial aerosols are presented.