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NIRE Annual Report
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 1999

Photolytic Behavior of Polycyclic Aromatic Hydrocarbons in Deposited Diesel Particulate Matters

Excited State Chemistry Division
Atmospheric Environmental Protection Department
Objectives
Photochemical reaction of polycyclic aromatic hydrocarbons (PAHs), of which mutagenic and/or carcinogenic effect is suspected, in diesel particulate matter (DPM) has been studied in gas-phase so far, but little is known about reaction of PAHs deposited on soil as particulates. This study was carried out to know photolytic behavior of PAHs in deposited DPM. Rates of photodegradation (oxidation reaction) for PAHs in DPM and the effects of soil component and rainwater on them have been studied using model systems.
Results
A standard reference material NIST SRM 1650 was used as a sample of DPM and it was irradiated in air using the light from a xenon lamp (170 mW/cm2). Table 1 shows rates of photodegradation(%) for PAHs in DPM under irradiation for two hours.
Some PAHs such as An, BaAn and BaPy degrade very quickly although no catalytic effect was given from others. We think that degradation of PAHs in DPM mainly occur by direct photolysis and photosensitized reaction. Effects of soil component and rainwater were studied for Frt, Py and Ch, which showed low rates in Table 1. Table 2 shows the rate of photodegradation obtained using a mixture of DPM and soil(5:95) and one soaked in nitric acid solution(24.4mg/ml) and dried.
The rates obtained on the DPM/soil sample were not largely varied from those for DPM(Frt:15.8, Py:16.9, and Ch:10.5). Namely, the effect of soil component was regligible or small. The effect of nitric acid solution (a model of rainwater) was also small. The rates of dissolution of PAHs from DPM to the solution was below 20% and these rates were used for correction. Table 2 shows degradation(%) obtained for a soaked DPM/soil sample. All values were
small compared with data obtained on DPM. A sample soaked in a sulfuric acid solution also showed similar results. These results indicate that stable PAHs in DPM remain and are accumulated in soils or sediments.

Table 1 and 2

Selected Publications
1) Photolytic behavior on soil of polycyclic aromatic hydrocarbons exhausted from diesel cars, 38th Annual meeting of the Japan Society for Atmospheric Environment, Tsukuba, Japan, September 23-25, 1997. 
2) Effect of soil component and rainwater on photodegradation of polycyclic aromatic hydrocarbons in deposited diesel particulate matters, 15th International aerosol conference, Edinburgh, Scotland, September 13-18,1998.

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