Abstract: In establishing the rate of air pollution is required a simple method and apparatus for determining the amount of particles in a gaseous medium.This is achieved with a tube-shaped sampler provided with means for establishing an isokinetic flow therethrough and having a high-tension connected rod-formed emission electrode disposed therein in insulated relationship relative to said tube, said tube being connected to ground for establishing a force of field giving the tube a function as collecting electrode.The sampler is placed in the flow of gas to be determined upon with its longitudinal direction substantially aligned with the flow direction. The particles collected in the sampler tube during a predetermined time is weighed and the result is possibly related to the difference in areas between sampler and gas flow for establishing the mass of particles per unit of time.