Abstract: A thin film method was introduced. It was applicable for the detection of individual atmospheric aerosol particles by using electron microscope. The particles could be identified through the morphologies of themselves or the products of the reactions between the particles and chemical reagents. From the distributions of the particles on the film, it was possible to deduce the distributions of the particles in the atmosphere based on the electric pump rate，the sampling time and the collection efficiency. This method is applicable not only for surface observation but also for balloon and aircraft observation.