I. REVIEW OF PROGRESS DURING THE PAST YEAR The objective of this work is to characterize the interactions of coal fly ash with polycyclic aromatic hydrocarbons (PAHs) and their derivatives, and to understand the influence of the surface properties of coal ash (and other atmospheric particles) on the chemical transformations of polycycllc aromatic compounds. Specific investigations directed toward this overall objective include: (a) Fractionation of heterogeneous coal fly ash samples into different particle types varying in size and chemical composition (carbonaceous, mineralmagnetic, and mineral nonmagnetic); Progress in the previous twelve-month perlod (November I, 1992-October 31, 1993) is summarized below. A. PHOTOTRANSFORMATION OF I-NITROPYRENE SORBED ON FLY ASH FRACTIONS Nitro derivatives of PAHs (commonly called "nitro-PAHs") are of significant concern because they tend to be much more toxic, mutagenic, and carcinogenic than parent PAHs [1,2]. Nitro-PAHs can be formed in the atmosphere by gas-phase reactions of PAHs with OH radical in the presence of NO2; once formed, the nitro-PAHs (which are significantly less volatile than the parent PAHs) tend to sorb onto particulate matter [3]. Hence, the influence of particulate surfaces o_ _.