NEPHELOMETER OPTICAL-RESPONSE MODEL FOR THE INTERPRETATION OF ATMOSPHERIC AEROSOL MEASUREMENTS

A numerical model evaluating the response of a typical integrating nep helometer is described. The model incorporates the actual scattering g eometry as well as the effects of a finite light source, detector size , and a nonideal Lambertian diffuser. An angular scattering weighting function is introduced to provide a tractable approach in numerical ca lculations and easy application. Using established size distribution e nsembles associated with a few representative aerosol types, we compar e the calculated response of a real nephelometer with that of an ideal . or perfect, nephelometer. The results indicate that, frequently, the nephelometer-produced aerosol-scattering coefficient is of the order of 10-20% too small; but for some naturally occurring aerosols, the di fference may be as large as 40-50%. For a multiple-wavelength nephelom eter, the response model can be employed to estimate the expected erro r in the aerosol-scattering coefficients directly from the measurement s themselves. (C) 1997 Optical Society of America.