STRUCTURAL VARIATIONS IN INDIVIDUAL CARBONACEOUS PARTICLES FROM AN URBAN AEROSOL

We have used transmission electron microscopy with electron energy-loss spectroscopy (EELS) to characterize the structures of carbonaceous aerosol particles from Phoenix, AZ. The particles are less-than-or-equal-to 2 mum in diameter and consist of tens to hundreds of aggregated spherules. EELS reveals a range of carbon structures, from amorphous to graphitic, within aggregates. Structural variations occur among individual spherules, on a scale of approximately 0.05 mum. The energy-loss data suggest combinations of single, double, and triple carbon bonds, implying the presence of both organic and elemental carbon. We interpret the graphitic domains as part of the primary spherules and the amorphous areas as condensed hydrocarbons. Surface coatings occur on carbonaceous aggregates collected in the summer months. The coatings contain oxygen, nitrogen, and sulfur. Coated aggregates have carbon structural variations similar to uncoated aggregates. The coatings are interpreted as sulfates and nitrates deposited from the atmosphere as end products of photochemical reactions.