Photochemistry of phenanthrene, pyrene, and fluoranthene in ice and snow

Although polycyclic aromatic hydrocarbons (PAHs) are common pollutants in snow, there is little quantitative data about their rates of photodegradation in this environment. To begin to address this gap, we have measured the degradation kinetics of phenanthrene, pyrene, and fluoranthene on ice, as th...

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Bibliographic Details
Published in:Atmospheric environment (1994) 2009-05, Vol.43 (14), p.2252-2259
Main Authors: Ram, Keren, Anastasio, Cort
Format: Article
Language:English
Subjects:
Applied sciences
Earth sciences
Earth, ocean, space
Engineering and environment geology. Geothermics
Exact sciences and technology
Greenland
Kinetics
Natural water pollution
PAHs
Persistent organic pollutants
Photodegradation
Pollution
Pollution, environment geology
Rainwaters, run off water and others
Water treatment and pollution
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Summary:Although polycyclic aromatic hydrocarbons (PAHs) are common pollutants in snow, there is little quantitative data about their rates of photodegradation in this environment. To begin to address this gap, we have measured the degradation kinetics of phenanthrene, pyrene, and fluoranthene on ice, as these are the most abundant PAHs in arctic snow. Frozen aqueous solutions of individual PAHs, with and without added hydrogen peroxide (HOOH) as a source of hydroxyl radical ( OH), were illuminated with simulated sunlight. For all three PAHs, direct photodecay is the main mechanism of degradation, while OH-initiated indirect photodegradation is a minor sink. Rate constants (±1 SE) for direct photodegradation extrapolated to midday, surface snow conditions at Summit, Greenland on the summer solstice are 3.8 (±0.8) × 10 −5, 28 (±3) × 10 −5, and 1.4 (±0.7) × 10 −5 s −1 for phenanthrene, pyrene, and fluoranthene, respectively. Apparent quantum efficiencies for photodegradation with simulated sunlight were 3.8 (±0.8) × 10 −3, 4.3 (±0.5) × 10 −4, and 2 (±1) × 10 −5, respectively. Calculated PAH lifetimes in surface snow under Summit conditions are 1–19 h during mid-summer, but increase to >100 days in the dark winter. While the short photodegradation lifetimes in the summer suggest that there should be no appreciable PAH levels in this season, past measurements at Summit sometimes show significant levels of these PAHs in summer surface snow. This discrepancy is likely due to differences in PAH location between lab samples (where the PAHs are probably in quasi-liquid layers) and real snow (where PAHs are likely primarily associated with particulate matter).
ISSN:1352-2310
1873-2844
DOI:10.1016/j.atmosenv.2009.01.044