Fractal geometry of carbonaceous aggregates from an urban aerosol

The 38 aggregates analyzed, ranging in length from 0.21 to 2.61 μm were divided into three groups: fractal (D<2), possibly nonfractal (D≥2), and mixed geometry. For the 23 fractal aggregates, fractal dimensions (D) range from 1.35 to 1.89 and are interpretable using cluster-cluster and particle-cluster models, which are variations of diffusion-limited aggregation. The 23 aggregates with D≥2 were divided into two categories: uncoated and coated. The uncoated aggregates have branching shapes and may have formed through particle-cluster aggregation. The coated aggregates have an underlying morphology which may be fractal; the coatings were probably deposited from the ambient atmosphere. The two mixed aggregates have interiors with D≥2 surrounded by outer regions with D<2. -from Authors