The gravimetric method of measuring PM10 particulate concentration in air is the reference method used in Poland and in the European Union. To get information on mass fractions of lower diameter particulates (e.g. PM5, PM2,5 or PM1) one usually has to apply various pre-sorters (most often of the impact type). This paper presents a new device that measures air particulate sizes in real time. The device makes it possible to classify (sort) air particulates according to size into 256 granularity classes from about 0.4 µm up to 300 µm. Tests of a device prototype were conducted in Warsaw at the turn of 2005/2006.