Atmospheric Concentrations of PCDDs/PCDFs in Southern California

Gas-phase atmospheric chemistry of dibenzo-p-dioxin and dibenzofuran

“…As for other organic compounds, in the atmosphere the PCDDs and PCDFs will be partitioned between the gas and particle phases (31). Bidleman (31) has estimated that 20-60% of the tetrachlorodibenzo-pdioxin should exist in the gas phase in urban and background air at 293 K. This expectation is in agreement with several ambient air studies (13, 14, [22][23][24][25][26][27].…”

“…Polychlorodibenzo-p-dioxins (PCDDs) and polychlorodibenzofurans (PCDFs) are emitted into the atmosphere, largely from the combustion of chlorine-containing materials (see, for example, refs 1-10), and numerous measurements of the concentrations of the tetrachlorothrough octachlorodibenzo-p-dioxins and dibenzofurans in ambient air have been reported (1,(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27). Interestingly, to our knowledge the monochloro-, dichloro-, and trichlorodibenzo-p-dioxins and dibenzofurans have not been measured in ambient air, although they have been observed in wood-burning emissions (10) and dibenzofuran has been observed in ambient air in urban (28) and remote (29) locations.…”

Transfer of dioxin risk between nine major municipal waste incinerators in Taiwan

“…We first defined the areas of 8 Â 8 km around each of nine incinerators, which were divided into 1600 sectors by a Cartesian grid, as our potential incinerator impact areas. Second, the industrial source complex short-term model (ISCST3) was used to estimate each dioxin congener's ambient concentrations and depositions in every sector within the impact areas, which was 200 Â 200 m. We modeled dioxin's dispersion in vapor and particle phases separately and incorporated their vapor -particle partition to obtain average air concentrations and depositions in each sector (Hunt and Maisel, 1992;USEPA, 1994a). Third, ISCST-modeled air-deposition rates were used to calculate the concentrations of each congener in the soil of each sector, considering firstorder transport and loss mechanisms of volatilization, erosion, surface runoff, leaching, and degradation (USEPA, 1993(USEPA, , 1994b.…”

Rate Constants for the Gas-Phase Reactions of the OH Radical with Dichlorobiphenyls, 1-Chlorodibenzo-p-dioxin, 1,2-Dimethoxybenzene, and Diphenyl Ether: Estimation of OH Radical Reaction Rate Constants for PCBs, PCDDs, and PCDFs

“…In the atmosphere, the PCDDs, PCDFs, and PCBs are partitioned between the gas and particle phases, with the major determining factor being the liquid-phase vapor pressure at the ambient atmospheric temperature (49,50). Based on theoretical considerations of gas-particle partitioning (49,50) and the results of several ambient air studies {13,19, 20, [31][32][33]35,37,38), at ~298 K the PCDDs, PCDFs, and PCBs with five or less chlorine atoms are expected to be present in the atmosphere at least partially in the gas phase, with dibenzo-p-dioxin, dibenzofuran, and biphenyl being ~100% in the gas phase and 2,3,7,8-tetrachlorodibenzo-p-dioxin being estimated to be ~40% in the gas phase (49).…”