Fine particulate matter smaller than 10 microns are considered a health hazard. Traditional gravimetric measurements of fine particulate matter entail the weighing of a filter using a microgram balance. The procedure takes time and the instrument can give only a 24-hour average PM concentration.

An alternative method is to focus a laser beam at the aerosol stream and detect the scattered light, which is proportional to the PM concentration. Both the gravimetric and the optical method use an inertial impactor to separate the coarse from the fine particles. Previous projects have successfully tested a locally fabricated inertial impactor.

Experiments are under way to determine the system parameters to be used for a prototype instrument. The initial set-up consists of a 780 nm laser diode, a photodiode, lenses, and a lock-in amplifier.