A model to evaluate half-lives of PAHs naturally occurring on airborne particulate.

Constant decay of polycyclic aromatic hydrocarbons (PAHs) adsorbed onto airborne particulate collected in glass fibre filters and exposed to sunlight ranged from 1.8 to 4.4 X 10(-3) (min-1), corresponding respectively to a half-life of 100 and 425 min. Half-life of PAHs appeared to be positively correlated with filter loading. Experimental results showed that decay of PAHs adsorbed on airborne particulate was induced by two concomitant reactions; a photochemical reaction involving the outer layers of collected particulate, and a "dark" reaction that may occur in the inner layers. The constant decays of these two reactions were calculated using a simplified mathematical model. The authors suggest the use of this model to compare chemical stability of airborne PAHs exposed, during their permanence in the atmosphere, to different physical (light intensity, temperature, humidity) as well as chemical conditions (oxidant concentration, chemical composition of particulate).