ATMOSPHERIC BEHAVIOR OF POLYCHLORINATED DIBENZO-P-DIOXINS AND DIBENZOFURANS AND THE EFFECT OF COMBUSTION TEMPERATURE

Emissions from the combustion of wood chips treated with pentachloroph enol (PCP), polyvinyl chloride (PVC) plastic pipe shavings, and solid PCP were injected into 25-m(3) outdoor Teflon film chambers and aged i n sunlight under typical atmospheric conditions. The behavior of parti culate and gas-phase polychlorinated dibenzo-p-dioxins and dibenzofura ns (PCDDs and PCDFs) and polycyclic aromatic hydrocarbons (PAHs) was m onitored over time. Only the tetra- and pentachlorinated dioxins and f urans were shown to clearly partition at all into the gas phase in the se experiments, perhaps due to high concentrations of TSP. Little or n o reactivity was observed for PCDDs and PCDFs residing on particles re sulting from high-temperature combustion (760-800 degrees C). Greater photochemical reactivity of particle-bound PCDD/Fs resulted after low- temperature combustion (350-380 PC), where fairly rapid photolysis com peted with a production mechanism believed to begin with PCP. Photolys is rates of PCD D/Fs appeared to increase with decreasing levels of ch lorination, lending evidence to the observed enrichment of the higher chlorinated species in the natural environment. On low-temperature com bustion particles, model results showed that TCDD half-lives increased from 0.4 under North Carolina summer outdoor conditions to 17 h under wintertime conditions. For high-temperature combustion particles unde r similar outdoor conditions, half-lives ranged from 6.8 to 62 h. For these same conditions, model OCDD half-lives increased from 5 and 38 h in low-temperature combustion experiments to 36 and 257 h in high-tem perature combustion experiments. Experimental particle-phase PAH photo lytic half-lives also increased from between 0.1 and 3.6 h in low-temp erature combustion experiments to between 4.4 h and stability on high- temperature combustion particles. These differ-ences may be explained by differences in the particles generated from low- and high-temperatu re combustion.