EMPIRICAL-FORMULA FOR INFRARED EXTINCTION BY AEROSOL-PARTICLES OF BRASS-70CU 30ZN/

An empirical formula for calculating the IR extinction of aerosol part icles of brass 70 Cu/30 Zn over the IR frequency range was derived bas ed on extensive calculations made on a body-center-like model having a widely varying number of particles ranging from 3.2 x 10(4) to 2.56 x 10(5). The expansion coefficients in the empirical formula were deter mined by the least squares curve fitting ot numerical data obtained us ing the finite difference time domain (FDTD) method. The formula satis fied the frequency dependence of the extinction in the frequency range from 2.143 x 10(13) to 3.75 x 10(13) Hz. The expression for the reson ant particle size (d0) and the constant coefficients in the empirical formula were derived in terms of the wavelength lambda, particle size d, and number of the primary particles N of aerosol particles. Numeric al results that were obtained from the empirical formula generally agr eed well with those calculated by the FDTD method tor aerosol particle s of brass 70 Cu/30 Zn with a magnitude of particle size in the range from 0.02 to 0.5 mum. The average error in the extinction calculation was less than 5%. The formula thus provides a simple and inexpensive m ethod for calculating the IR extinction of aerosol particles, which ot herwise requires complicated and expensive calculation methods.