Morphology distributions and chemical composition of size-selected atmospheric fine particles.

摘要

Morphology distributions of atmospheric fine particles were obtained for four sizes of particles in the cities of East Hartford, CT and Baltimore, MD. Particle morphology was characterized through the use of structural border-based fractal dimensions. East Hartford, CT sampling was conducted during the Fall of 2001, Winter 2002, and Summer of 2002. Baltimore, MD sampling was conducted during the Fall of 2002. Three different periods of the day were sampled in East Hartford: early morning, noon, and night. Four different periods of the day were sampled in Baltimore: early morning, noon, afternoon, and night. The sampling period in Hartford, CT was three hours while in Baltimore, MD, it was one hour.; Stages 1, 4, 6, and 8 of a Berner-type Low Pressure Impactor (BTLPI) were used for particle morphology analysis. These stages correspond to mean aerodynamic diameters (d50) of 0.10 mum, 0.15 mum, 0.55 mum, and 2.0 mum, respectively. Particles found on stage 4 (d50: 0.15 mum) showed high fractal dimension values at both sites. Particles impacting on stage 8 (d50: 2.0 mum) showed low fractal dimension values at both sites. Times of the day with high traffic conditions may result in higher fractal dimensions due to the higher amount of soot particles present. Particle fractal dimension distributions in stage 4 early morning sampling were significantly different from stage 4 night sampling for both sites, and showed higher values for fractal dimensions.; Particle fractal dimension distributions in stage 8 early sampling were not significantly different from stage 8 night sampling for both sites, and showed values close to one. Fractal dimensions values in stage 8 varied less than fractal dimensions in stage 4 through all the different seasons sampled in East Hartford. Stages 1 and 6 show more variability in fractal dimension values obtained in East Hartford, CT, and Baltimore, MD.; Energy dispersive spectroscopy on particles belonging to stage 4 in both sites (E. Hartford, CT and Baltimore, MD) suggested that elemental carbon is the major component of fractal-like aggregates. Heterogeneous fractal-like particles containing sulfur, iron, potassium, and silica, were present in East Hartford and Baltimore samples.