OPTICAL COUNTER RESPONSE TO MONODISPERSE ATMOSPHERIC AEROSOLS

The response of a single particle optical counter to monodisperse fractions of ambient Los Angeles aerosols was determined. The monodisperse atmospheric aerosols were obtained using a differential mobility analyzer to select particles of a uniform geometric diameter. The optical counter response for atmospheric aerosols was compared to that for polystyrene latex spheres and to oleic acid particles of the same geometric diameter. Measurements were done with a Particle Measuring Systems (Boulder, CO) LASX optical counter of the type used for the Southern California Air Quality Study. The responses to atmospheric particles with diameters of 0.30, 0.38, 0.497 and 0.624-mu-m were measured at different times between 16 and 30 July 1987. The atmospheric aerosols were found to scatter less light than polystyrene latex particles (refractive index = 1.59-0.0i), but about the same amount of light as oleic acid spheres (1.46-0.0i) of the same geometric diameter. On several occasions it was found that atmospheric particles of 0.497-mu-m geometric diameter produced two distinct optical diameters, indicating heterogeneity in composition among individual particles of this size.