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POLYCHLORINATED DIBENZO-P-DIOXINS AND DIBENZOFURANS: GAS-PHASE HYDROXYL RADICAL REACTIONS AND RELATED ATMOSPHERIC REMOVAL. (R825377)
Citation:
Hites, R. A. AND W. W. Brubaker. POLYCHLORINATED DIBENZO-P-DIOXINS AND DIBENZOFURANS: GAS-PHASE HYDROXYL RADICAL REACTIONS AND RELATED ATMOSPHERIC REMOVAL. (R825377). ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 31:1805-1810, (1997).
Description:
Gas-phase reactions with the hydroxyl radical (OH) are
expected to be an important removal pathway of polychlorinated dibenzo-p-dioxins and dibenzofurans
(PCDD/F)
in the atmosphere. Our laboratory recently developed
a system to measure the rate constants of the gas-phase
reactions of OH with semivolatile organic compounds
using on-line mass spectrometry. We have now
incorporated
electron capture mass spectrometry (EC-MS) into this
system to increase its sensitivity to PCDD/F, which tend
to
have low vapor pressures. OH reaction rate constants
were determined in helium for
1,2,3,4-tetrachlorodibenzo-p-dioxin at 373-432 K using a heated quartz reaction
chamber.
The photolysis of O3 in the presence of
H2O and the
photolysis of H2O2 (both at 
= 254 nm)
served as OH sources.
An extrapolation using the Arrhenius equation gives a
1,2,3,4-tetrachlorodibenzo-p-dioxin-OH reaction rate constant
of
8.5 × 10-13 cm3
s-1 at 298 K, which is in excellent
agreement
with the value predicted by a structure-activity method.
The
predicted OH reaction rate constants for tetra- through
octachlorodibenzo-p-dioxin and dibenzofuran isomers
were
used in a simple model of the atmospheric removal of PCDD/F. The results of our model indicate that atmospheric
removal is a combination of gas-phase removal processes
of lower chlorinated dioxins and furans and particle-phase removal processes of higher chlorinated
ones.