Polycyclic Aromatic Hydrocarbons in Rainwater Collected in a Tropical Polluted Urban Area

Abstract

Polycyclic aromatic hydrocarbons present in rainwater were studied in two distinct areas in Mexico City Metropolitan Area throughout the rainy season. The results showed no significant difference between the two sites, thus suggesting a more regional phenomenon driving the dissolution of the PAHs in the rain. The PAHs concentration ranged from 1.7–30.2 ngL⁻¹with the predominance of phenanthrene, fluoranthene, and pyrene. The PAH sources were traced predominantly to vehicular emission with signature PAHs, diagnostic ratios, and cluster statistical analyses. On the other hand, the temporal analysis of the PAHs showed that the fluxes of the Total PAH were slightly different for both sites. The urban-industrial site showed fluxes that ranged from 145–3263 ng m⁻²d⁻¹, while the urban site ranged from 134–3139 ng m⁻²d⁻¹, with the urban site having a moderate rate at which the total PAHs diminished throughout the rainy season while the urban-industrial showed no change throughout the rainy season. This study also addressed two occurrences when studying PAHs in rain: the degradation of PAHs in the samples with acidic rain and the dilution of the PAH in the samples with continued collection of rain.

Key Words:

• degradation
• dilution effect
• Mexico City
• PAHs
• rainout

ACKNOWLEDGMENTS

We would like to thank Dr. Hugo Padilla Gordon from Centro de Ciencias de la Atmósfera, UNAM for his invaluable comments.