Polycyclic aromatic hydrocarbons in a suburban atmosphere.: 3.: Size distribution.

Aerosol samples in the atmosphere of Jinamar valley have been collected and size-fractionated during 7 days period using five-stage cascade impactor. Aerosol particles were separated into six size fractions. The samples were analyzed for polycyclic aromatic hydrocarbons (PAHs) with molecular weights between 128 and 276, using gas chromatography/mass spectrometry. The distributions of phenanthrene, anthracene, pyrene and fluoranthene with particle size are nearly identical. Sigma PAHs shows a similar unimodal structure with the mode in the 3.8-7.4 pm size range. Benzo(a)anthracene exhibit a bimodal character with modal diameters in 0.3-0.9 mum and 3.8-7.4 mum. Mass median diameters range from 1.37 (chrysene) to 2.51 (anthracene) for PAHs with molecular weights less than or equal to 228. Higher molecular weight PAHs are associated with particles less than 2 mum.