Instrument for long-path spectral extinction measurements in air: application to sizing of airborne particles

A novel instrument that is capable of taking spectral extinction measuremen ts over long optical paths (approximately 1-100 m) in the UV, visible, and IR ranges is described. The instrument is fully automated, and the extincti on spectrum is acquired in almost real time (approximately 5-10 s) with a r esolution of similar to3 nm. Its sensitivity and accuracy were estimated by tests carried out in a clean room that showed that, for optical paths betw een 50 and 100 m, the extinction coefficient can be detected at levels of s imilar to 10(-5) m(-1). Tests carried out on calibrated latex particles sho wed that, when it was combined with an appropriate inversion method, the te chnique could be profitably applied to characterize airborne particulate di stributions. By carrying out measurements over optical paths of similar to 100 m, the instrument is also capable of detecting extinction coefficients that are due to aerosol concentrations well below the limits imposed by the European Economic Community for atmospheric pollution (150 mug/m(3)). Scal ed over optical paths of similar to 10 in. the limit imposed for particle e missions from industrial plants (10 mg/m(3)) can also be detected sensitive ly. (C) 2001 Optical Society of America.