Absorption of light by soot particles in micro-droplets of water

Absorption cross section of carbon soot clusters inside water microdroplets is calculated. Fractal geometry of carbon inclusions is considered with the fractal dimension D in the interval 1 less than or equal to D less than or equal to 3, which includes the trivial geometry (D = 3) as a limiting case. It is found that the absorption cross section of a soot cluster inside a water droplet is increased, compared to that in vacuum, by the factor of approximate to 16 for the practically important case of D = 1.8. This result is obtained by averaging of the enhancement factor over the diffraction parameter of the microdroplets x = ka (k = 2 pi/lambda), a is the radius of the microdroplet) with a fine resolution. It is shown that the narrow resonances in the enhancement factor as a function of x play important role and should be taken into account for the purpose of averaging over x. The absorption enhancement factor increases, on average, when D decreases, and reaches the value of approximate to 22 for D = 1. (C) 1999 Elsevier Science Ltd. All rights reserved.