Fractal geometry of carbonaceous aerosol particles as determined using Transmission Electron Microscopy

Abstract

Carbonaceous aggregates collected from the aerosol of Phoenix, Arizona have an irregular branched morphology. The aggregates resemble combustion soots and were probably emitted by motor vehicles. Fractal analysis provides a means of quantifying morphologic variations among aggregates and relating these variations to mechanisms of formation. Bright-field transmission electron microscope (TEM) images of 38 individual aggregates were recorded on negatives at magnifications of 15,000 to 200,000. The aggregates have maximum lengths ranging from 0.21 to 2.61 μm and are composed of interconnected spherules, each averaging 26 nm in diameter. The number of spherules in each aggregate ranges from 32 to 1842; the average number is 551. “The nesting squares” method of fractal analysis was applied to digital binary images to calculate the fractal dimension (D) of each aggregate.