The paper describes an electrooptical instrument for monitoring the atmospheric pollution due to dust, based on the scattering phenomena. A so called ‘aerosol’ is formed by a sampling tube, driven by a cosntant delivery air-suction pump. The sampling tube is placed before a collimating light source and the scattered light is transmitted through an optical lens systems consists of directional iris and then collected by a photomultiplier tube. The outpur voltage of the photomultiplier which is a function of particle size and concentration, is fed to a log amplifier and then to a ‘digital signal processing system’. The DSPS discriminates the particles according to the size and is developed utilizing latest CMOS integrated circuits. It consists of level detection of pulses, their classification according to their level, counting of pulses and storage of data. Both the count data and real time is printed by aminiature drum head printer. The instrument is suitable for dust concentration in two ranges, 107 and 102 particles per cubic meter of air, and of size 0.1 and 10 mm; and is portable, battery operated.