Final Report: A Study of the Gas/Particle Partitioning of Chlorinated Dibenzodioxins (CDDs) and Chlorinated Dibenzofurans (CDFs) to Ambient and Model Aerosol Materials

EPA Grant Number: R825376
Title: A Study of the Gas/Particle Partitioning of Chlorinated Dibenzodioxins (CDDs) and Chlorinated Dibenzofurans (CDFs) to Ambient and Model Aerosol Materials
Investigators: Pankow, James F.
Institution: Oregon Graduate Institute of Science & Technology
EPA Project Officer: Shapiro, Paul
Project Period: October 1, 1996 through September 30, 1999
Project Amount: $466,448
RFA: Exploratory Research - Air Engineering (1996) RFA Text |  Recipients Lists
Research Category: Air Quality and Air Toxics , Land and Waste Management , Air , Engineering and Environmental Chemistry

Objective:

Construct a Linear Free Energy Relationship to predict the gas/particle partitioning behavior of the polychlorinated dibenzodioxins and dibenzofurans to ambient aerosols.

Summary/Accomplishments (Outputs/Outcomes):

The overall goal of this research project was to gain a better understanding of how the physical-chemical properties of the SOC and particle phase affect the G/P partitioning of SOCs, and to improve the accuracy and universality of log Kp vs. log correlations for PCDD/Fs and PAHs.

G/P distributions of SOCs in the atmosphere are often measured using filter/sorbent samplers. Temperature and relative humidity fluctuations during sampling and the adsorption of gaseous SOCs onto filter surfaces can cause errors in the measured G and P-phase SOC concentrations (Cg and Cp ) and Kp values. Controlled field experiments (CFEs) minimize sampling artifacts. CFEs were conducted by equilibrating previously collected ambient particulate materials with SOCs generated in the gas phase using particle free ambient air maintained at a specific temperature (T) and relative humidity (RH) to prevent their diurnal cycling. A backup filter was used to correct for gas adsorption to the filter surface. Results were presented from field trials of CFEs conducted in Beaverton, OR; Denver, CO; and Hills, IA.

The adsorption of gaseous PCDD/Fs and PAHs to TMF and QFF was studied so that the magnitude of the influence of gas adsorption artifacts on measured values of Cg and Cp and Kp could be evaluated. For TMF's, sorption isotherms of PCDD/Fs and PAH were linear over three orders of magnitude. A 10 degree change in T caused the Kp,s values to decrease by factors of 2.4 to 3.4. Changes in RH between 21 and 52 percent did not affect the measured Kp,s values. The dependence of the partitioning on the of the subject compounds was investigated. Within each of the three individual compound classes, plots of log Kp,s vs. log were linear with slopes of approximately -1. The pooled data for the three compound classes yielded a single log Kp,s vs. log plot for 25?C that was correlated nearly as well (r2 = 0.96) as the plots for the individual compound classes (r2 0.95).

For QFF, within each of the three individual compound classes, plots of log Kp,s vs. log were found to be linear with slopes of approximately -1. At RH = 25 percent, the pooled log Kp,s data at 25oC for the three compound classes were correlated with log nearly as well (r2 = 0.95) as were the data for the individual compound classes (r2 0.97). In general, the Kp,s values for the PAHs and PCDD/Fs studied were found to be about a factor of two larger for partitioning to clean QFFs at RH = 25 percent than for TMFs at RH = 21-52 percent. Backup QFFs used in filter/sorbent sampling in suburban areas yielded Kp,s values for PAHs at RH = 37 percent that were significantly lower than for clean QFFs at the same RH. This may have been the result of the adsorption of ambient organic compounds that at least partially blocked the direct adsorption of the SOCs to the QFF surface. Therefore, when QFFs are used to separate atmospheric gas- and particle-phase SOCs, corrections for compound-dependent gas adsorption artifacts for QFFs should probably be carried out using Kp,s values that were obtained with ambient backup QFFs.

Using the preceding data, the adsorptive affinity of TMF and QFF for gaseous PCDD/Fs and PAHs was compared and a model developed to predict the magnitude of the influence of gas adsorption artifacts on measurements of Cg , Cp and Kp. The examination was based on values of Kp,x (m3/cm2), which is the partition coefficient expressed as [ng sorbed/cm2 of filter face] / [ng/m3 in gas phase]. At RH values below " 54 percent, the Kp,x values for PAHs are lower on TMFs than on ambient backup QFFs. The gas adsorption artifact will therefore be lower with TMFs than with QFFs for these compounds under these conditions. Corrections for this artifact have been made in the past by using a backup filter, and subtracting the mass amount of each compound found on the backup filter from the total (particle phase + sorbed on filter) amount found on the front filter. This procedure assumes that the ng/cm2 amounts of each SOC sorbed on the front and backup filters are equal. Since the front filter will tend to reach equilibrium with the incoming gaseous SOCs first, that equality might only be achieved after both filters have reached equilibrium with the gaseous SOCs in the sample air. The minimum air sample volume Vt,min required to reach gas/solid sorption equilibrium with a pair of filters is (Kp,x ' 2 ' Afilter) where Afilter (cm2) is the per-filter face area. Kp,x values, and therefore Vt,min values, depend on the compound, RH, T, and filter type. Compound-dependent Vt.min values were determined for both TMFs and QFFs. A model was developed which could be used to predict the magnitude of gas adsorption artifacts on Cg , Cp and Kp values as a function of the compound class, RH, T and filter type. The model accurately fit available measured data. Model results indicate that some of the backup-filter-based corrections described in the literature were carried out using sample volumes that were smaller than the Vt,min values for some compounds of interest. For these studies gas adsorption artifacts may have still influenced measurements of Cg and Cp despite corrections made using backup filters.

To construct a correlation of log Kp vs. log for a given class of SOCs, values as a function of T are required. Moreover information regarding the mechanism of G/P partitioning can be inferred from the value of slope (mr) of this correlation; the accuracy of the value of mr depends directly on the accuracy of the values used in the correlation. A systematic bias in the measured (or estimated) values of a homologues series of compounds can bias the value of mr. A dynamic gas saturation technique was used to directly measure the vapor pressures of 6 PAHs and 13 PCDD/Fs. The vapor pressures of the 6 PAHs were within a factor 1.5 compared to previously reported values obtained using a similar dynamic gas saturation technique. New measured vapor pressure data for 4 toxicologically significant, 2,3,7,8 substituted PCDD/F congeners and 4 non-2,3,7,8 PCDD/F congeners was significantly different than predicted values from the literature. The vapor pressure data suggests that a miscibility gap exists at room temperature for mixtures of solid phase PAHs and PCDD/Fs. Using the new vapor pressure data, four correlation methods were used to predict the vapor pressures of the PCDD/Fs at 25 ?C. A correlation between and gas chromatograph retention index (GC-RI) was the most precise and accurate. Parameters were determined for calculating the values of 210 PCDD/Fs as function of temperature. Measured PCDD/F data was used to evaluate estimates made using a GC-RI method with a single reference compound. A systematic difference between the measured and estimated values was observed and it was suggested that the ratio gtest / greference is variable throughout this class of compounds. It is suggested that should the GC-RI method be used in future measurements of the values of a homologues series of compounds (i.e., chlorinated naphthalenes or chlorinated paraffins), at least one reference compound at each level of chlorination should be used to minimize systematic differences between pgc and .

Conventional high volume air sampling was used to measure ambient gas and particle-phase PAHs at an urban, suburban and rural site in Denver, CO; Beaverton, OR; and Hills, IA, respectively. The particle-phase organic (OC) and elemental (EC) carbon was also measured. Among these locations the weight fraction of particle-phase organic (foc) and elemental carbon (fec) ranged from 0.018 to 0.20 and from 0 to 0.262, respectively. Kp values were normalized by fec, where Kp,ec = Kp / fec. For samples taken during rain events the variation in the Kp values of PAHs with similar values was a factor one and a half among the three samples, but there was no significant difference in the Kp,ec values. A correlation between EC and ?PAH particle-phase concentration was observed for samples taken during rain events in Beaverton.

At the three field locations CFEs were used to determine the Kp values of PCDD/Fs and PAHs. Conventional high volume air sampling (HVOL) was also used to determine the Kp values of the PAHs. HVOL was conducted throughout the night and during rain events with changes of only 2 ?C in temperature and 10 percent the relative humidity (RH); backup filters were used to correct for gas adsorption artifacts. Plots of log Kp vs. log made using HVOL data had a slope shallower than -1 but plots made using data from CFEs had a slope nearer to -1. The values of Kp determined from both methods were similar for the low vapor pressure compounds but different for the higher vapor pressure compounds. It was suggested that for PAHs, slopes shallower than -1 may be due to the presence of non-exchangeable material present on the native particles. Model results suggest that the mass percent of the collected particles that was non-exchangeable ranged from 0.6 to 1.73 percent.

To compensate for differences in the organic matter content and organic carbon content of particles among locations, Kp values were normalized by the weight fraction of particle-phase organic carbon (foc) and organic matter phase (fom), where Kp,om = Kp / fom and Kp,oc = Kp / foc. There was less variation in the Kp,oc and Kp,om values of compounds with similar values among locations than for Kp values. Among the three field locations and three studies from the literature, the Kp values of PAHs with similar values varied by over 2.5 orders of magnitude; the Kp,om and Kp,oc values varied by one order of magnitude. Variation in the Kp,om and Kp,oc values among locations may be due to error in the conversion factor relating foc to fom and/or differences in the chemical composition of particulate organic matter phases (OM) among locations and/or sources of particles. It appears that absorptive partitioning is important even for particles with small amounts of OC (foc < 0.02). Since 1) Particles from different sources and/or locations may have different amounts of OC (and OM) and 2) the OC (and OM) content may vary with time. If a log Kp vs. log correlation is to be used to predict G/P partitioning behavior of a given class of SOCs at another time and/or location Kp values should normalized by the foc of the collected particles or if the chemical composition of the particle phase is known by fom.


Journal Articles on this Report : 5 Displayed | Download in RIS Format

Other project views: All 5 publications 5 publications in selected types All 5 journal articles
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Journal Article Mader BT, Pankow JF. Gas/solid partitioning of semivolatile organic compounds (SOCs) to air filters. 1. Partitioning of polychlorinated dibenzodioxins, polychlorinated dibenzofurans and polycyclic aromatic hydrocarbons to teflon membrane filters. Atmospheric Environment 2000;34(28):4879-4887. R825376 (Final)
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  • Journal Article Mader BT, Pankow JF. Gas/solid partitioning of semivolatile organic compounds (SOCs) to air filters. 3. An analysis of gas adsorption artifacts in measurements of atmospheric SOCs and organic carbon (OC) when using Teflon membrane filters and quartz fiber filters. Environmental Science & Technology 2001;35(17):3422-3432. R825376 (Final)
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  • Journal Article Mader BT, Pankow JF. Gas/solid partitioning of semivolatile organic compounds (SOCs) to air filters. 2. Partitioning of polychlorinated dibenzodioxins, polychlorinated dibenzofurans, and polycyclic aromatic hydrocarbons to quartz fiber filters. Atmospheric Environment 2001;35(7):1217-1223. R825376 (Final)
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  • Journal Article Mader BT, Pankow JF. Study of the effects of particle-phase carbon on the gas/particle partitioning of sernivolatile organic compounds in the atmosphere using controlled field experiments. Environmental Science & Technology 2002;36(23):5218-5228. R825376 (Final)
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  • Journal Article Mader BT, Pankow JF. Vapor pressures of the polychlorinated dibenzodioxins (PCDDs) and the polychlorinated dibenzofurans (PCDFs). Atmospheric Environment 2003;37(22):3103-3114. R825376 (Final)
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  • Supplemental Keywords:

    organohalogen, fate, transport., RFA, Health, Scientific Discipline, Air, Water, particulate matter, air toxics, Environmental Chemistry, Risk Assessments, Air Deposition, Biology, Engineering, Engineering, Chemistry, & Physics, monitoring, dioxin, ambient aerosol, gas/particle partitioning, particulates, exposure and effects, food chain, toxicology, air sampling, human exposure, furans

    Progress and Final Reports:

    Original Abstract
  • 1997 Progress Report
  • 1998 Progress Report