The classical Ångström exponent is an operationally robust optical parameter that contains size information on all optically active aerosols in the field of view of a sunphotometer. Assuming that the optical effects of a typical (radius) size distribution can be approximated by separate submicrometer and supermicrometer components, we show that one can exploit the spectral curvature information in the measured optical depth to permit a direct estimation of a fine-mode (submicrometer) Ångström exponent (α<sub><i>f</i></sub>) as well as the optical fraction of fine-mode particles (η). Simple expressions that enable the estimation of these parameters are presented and tested by use of simulations and measurements.
© 2001 Optical Society of America
Norm T. O’Neill, Oleg Dubovik, and Tom F. Eck, "Modified Ångström Exponent for the Characterization of Submicrometer Aerosols," Appl. Opt. 40, 2368-2375 (2001)