Aggregates (composed of large numbers of primary particles) are produc
ed in many engineering environments. One convenient characterization i
s the fractal dimension, the exponent describing how the number of pri
mary particles in each aggregate scales with radial distance from its
center of mass. We describe a finite-analytic pseudo-continuum predict
ion of the normalized accessible surface area of an isothermal quasi-s
pherical fractal aggregate containing N (>> 1) primary particles, on t
he surfaces of which a first-order chemical process occurs. Results ar
e displayed for specific fractal dimensions (2.5, 2.18, and 1 8) frequ
ently observed in aggregating systems. An effective Thiele modulus is
used to develop an efficient and accurate scheme for predicting/correl
ating the effectiveness factor for an aggregate containing N primary p
articles in terms of aggregate fractal dimension, reaction probability
, and Knudsen number. Our methods now allow calculations of the access
ible surface area of populations of aggregates, provided pdf-(N, D(f),
...)- is known for the populations of interest.