Photolytic behavior of polycyclic aromatic hydrocarbons in diesel particulate matter deposited on the ground

To clarify the photolytic behavior of polycyclic aromatic hydrocarbons (PAH s) in diesel particulate matter (DPM) deposited on the ground, we determine d the rate constants and half-lives for the photodegradation of benzo[a]pyr ene (BaPy), phenanthrene (Phe), fluoranthene (Flrt), pyrene (Py), and chrys ene (Ch) in air for three probable cases: (1) DPM is placed on an inert sur face, (2) DPM is mixed with soil, and (3) PAHs are leached from DPM and ads orbed to soil. We found that BaPy and Phe degraded relatively quickly in ca se 1. However, in case 2, these PAHs degraded more slowly due to the effect of the presence of soil. Flrt, Py, and Ch were stable. In case 3, photodeg radation of adsorbed PAHs in soil was strongly inhibited as a function of s oil depth. Although these findings were obtained at extreme light intensiti es; they may occur under real world conditions. Conversion factors for obta ining rate constants and half-lives for PAHs on the ground under sunlight a re presented. We conclude that under the average intensity of sunlight in T okyo, photo deg ra dation of PAHs in DPM deposited on an inert surface is v ery slow.