The Particle Technology Group at Delft University of Technology is developing an instrument for on-line, real-time measurement of size and chemical composition of individual aerosol particles. Particles are sampled from an aerosol by using aerosol beam techniques. Collimated by the beam generator system the particles enter the ionization chamber of a time-of-flight mass spectrometer. There they are detected by the use of a photomultiplier when travelling through the beam of a small He-Ne laser and thereby scattering light. The photomultiplier signal is also used to trigger a Q-switched YAG laser which is vaporizing and ionizing the same particle. Analysis of the generated ions provides information on the chemical composition of the particles and the photomultiplier signal contains the particle size information.@en

This paper describes an on-line instrument, capable of measuring the size and chemical composition of single aerosol particles. Possible applications include monitoring aerosol reactors and studying atmospheric chemistry. The main conclusion is that a working prototype has been built and tested. It uses a three stage vacuum system to generate an aerosol beam with a low divergence angle and a high transmittance. The pressure is reduced sufficiently to allow the application of a time-of-flight mass analyzer. The aerosol beam is probed in the analysis section by the focused beam of a low-power helium-neon laser. Every particle crossing the laser beam scatters light, which is detected by two photomultiplier tubes, mounted at angles of 45 and 90°. The signal is stored when both detectors produce a pulse simultaneously, and this event triggers the chemical analysis cycle. A pulsed Nd: YAG laser vaporizes the particle and generates ions, which are next analyzed by a time-of-flight mass spectrometer. In this way combined information on the size and the composition of the particle is obtained.@en

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.@en