Determination of size and concentration of particles in air by using long path optical extinction measurements

Atmospheric particle pollution and particles emitted by industrial plants are extremely dangerous for human health. Indeed, they have diameters in such a range (approximately 0.1-5 μm) that they can penetrate our respiratory system, but cannot be expelled during exhalation. Therefore, it is extremely important to detect them and characterize their size distribution. In this paper we propose the use of a novel instrument recently developed by the authors for the monitoring of airborne particulate at concentration levels so to comply with the current European Economic Community (EEC) regulations. The instrument is based on spectral extinction measurements over long optical paths and is able to recover, almost in real time, both concentration and size distribution of particles with diameters in the range of interest. The sensitivity and accuracy of the instrument were estimated by means of measurements in a clean room and by using calibrated particles dispersed in water. Our results show that, by carrying out measurements over optical paths of approximately □100 m, the instrument is able to detect concentration levels well below the ECC limit imposed for the atmospheric pollution. Scaled over shorter optical paths (approximately 10 m), the limit imposed for particle emissions by industrial plants can also be detected very accurately.