The Met One Instruments, Inc. model ES-642 is a type of nephelometer which automatically measures real-time airborne PM10, PM2.5, or TSP particulate concentration levels using the principle of forward laser light scatter. Sample air is drawn into the ES-642 and through the laser optical module, where the particulate in the sample air stream scatters the laser light through reflective and refractive properties. This scattered light is collected onto a photodiode detector at a near-forward angle, and the resulting electronic signal is processed to determine a continuous, real-time measurement of airborne particulate mass concentrations. ES-642 AMBIENT PARTICULATE MONITOR Applications include rail and roadside monitoring, schools and playgrounds, underground facilities, solar power installations, wind energy installations, f...