Grantee Research Project Results
1998 Progress Report: Kinetics of Semi-volatile Organic Compounds and Hydroxyl Radical Reactions
EPA Grant Number: R825377Title: Kinetics of Semi-volatile Organic Compounds and Hydroxyl Radical Reactions
Investigators: Hites, Ronald A.
Institution: Indiana University - Bloomington
EPA Project Officer: Hahn, Intaek
Project Period: October 14, 1996 through October 13, 1999
Project Period Covered by this Report: October 14, 1997 through October 13, 1998
Project Amount: $356,212
RFA: Exploratory Research - Air Engineering (1996) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Air , Safer Chemicals , Land and Waste Management
Objective:
This project focuses on the atmospheric fates of polychlorinated dibenzo-p-dioxins and dibenzofurans and related compounds. Our goal is to obtain a detailed accounting of the behavior of these compounds while they are in the atmosphere. One of the largest gaps in our knowledge is rate constants of chemical degradation in the gas-phase. Therefore, our specific goal is to measure second-order rate constants for the reactions of these compounds with the hydroxyl radical (OH) in the gas-phase. The overall goal is to use these rate constants to develop a mass balance of emissions, degradation, and deposition. The latter goal has required some measurement effort focused on air collected over the remote north Atlantic.Progress Summary:
The main trick to making the rate constant measurement has been to actually get the compounds of interest into the gas-phase. We have done this with a heated, glass reaction chamber monitored directly by a mass spectrometer operated in the electron capture, negative ionization mode. Thus, we gain sensitivity by this highly selective and sensitive ionization technique. However, it turns out that there is a limit to the elevated temperature approach: The sources of OH also tend to decompose thermally as the temperature increases. We have worked around this limitation by using both O3/H2O and H2O2 as the OH source. As one might guess, the atmospheric concentrations of dioxins in air over the remote north Atlantic are very low; thus, the trick to making these measurements is to achieve ultra-high sensitivity. This we have done by the simple expedient of sampling or compositing very large volumes of air (up to 20,000 m3) and by using electron capture, negative ionization mass spectrometry to quantitate these samples. Some of this work has been published, and reprints are attached to this report.
Our laboratory measured the gas-phase reaction rate constants of polychlorinated biphenyls (PCBs) with the hydroxyl radical (OH) and concluded that OH reactions are the primary removal pathway of PCBs from the atmosphere. With the reaction system previously employed for kinetics, we have now investigated the products of these PCB-OH reactions. Experiments were carried out in either air or He as the diluent gas at approximately 1 atm, in a 160-mL quartz chamber. Temperatures ranged between 318-363 K in order to enhance the vapor pressures of these less volatile compounds. OH was produced in situ by the photolysis of ozone in the presence of H2O. Reaction products from biphenyl, the three monochlorobiphenyls, and five dichlorobiphenyls were extracted from the chamber, derivatized by diazomethane, and analyzed by gas chromatographic mass spectrometry. Experiments gave benzoic acid and the appropriate chlorinated benzoic acids in significant product yields (8-17%). See the attached reprint for details.
We have developed a sampling strategy that allows us to determine fg/m3 concentrations of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/F) in remote marine atmospheres. Using this sampling strategy, a total of 37 air samples were taken during two extended sampling periods at Bermuda between September 1993 and August 1997. During this time, the 35 ? 10 fg/m3, in the remote marine atmosphere. PCDD/F concentrations during both sampling periods were somewhat higher in the winter when air parcels originated from North America. A second air sampling station was established at Barbados where 22 air samples were taken between March 1996 and August 1997; an average total PCDD/F concentration at Barbados of 15 ? 7 fg/m3 was found. This value was not significantly different than the 27 ? 7 fg/m3 found at Bermuda during this time when air arrived from the east. This indicated that the remote marine background concentration for these compounds is currently on the order of 20 fg/m3. Using these background concentrations, the dry depositional rate of PCDD/F to the world's oceans was estimated to be 200 ? 80 kg/yr, and the wet depositional rate was estimated to be 900 ? 300 kg/yr. This is a total deposition rate of about 1 t/yr to the oceans as compared to our previous estimate of about 10 t/yr PCDD/F deposition from the atmosphere to the land.
Future Activities:
This project will terminate on 10/13/99. In the last year of this project, we will focus on mass balance issues. Our goal is to develop a good mass balance for PCDD/F on a homologue-by-homologue basis using the rate constants measured during the course of this project and using the atmospheric measurements outlined above. We have spent some considerable time re-working the US EPA's United States' PCDD/F emissions inventories, and we have developed a way of extrapo-lating these US only data to the rest of the world using country specific CO2 emission estimates. We have also spent considerable effort up-dating previous estimates of deposition. While we have not yet completed the work, it is clear that one cannot treat the global atmosphere as one environmental compartment. We are in the process of developing a more sophisticated model that will take into account the different reactivities of the different PCDD/F homologues to OH, the (presumably) lim-ited range of advection or transport, the relatively high deposition of PCDD/F within this limited range, and the relatively low deposition of these compounds to the oceans as measured in this project (see above).Journal Articles on this Report : 7 Displayed | Download in RIS Format
| Other project views: | All 20 publications | 8 publications in selected types | All 8 journal articles |
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Baker JI, Hites RA. Comment on "Evidence for the presence of PCDD/Fs in the environment prior to 1900 and further studies on their temporal trends." Environmental Science & Technology 1999;33(1):205. |
R825377 (1998) R825377 (Final) |
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Baker JI, Hites RA. Polychlorinated dibenzo-p-dioxins and dibenzofurans in the remote North Atlantic marine atmosphere. Environmental Science & Technology 1999;33(1):14-20. |
R825377 (1998) R825377 (Final) |
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Brubaker Jr. WW, Hites RA. Polychlorinated dibenzo-p-dioxins and dibenzofurans:gas phase hydroxyl radical reactions and related atmospheric removal. Environmental Science & Technology 1997;31(6):1805-1810. |
R825377 (1998) R825377 (Final) |
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Brubaker Jr. WW, Hites RA. Gas phase oxidation products of biphenyl and polychlorinated biphenyls. Environmental Science & Technology 1998;32(24):3913-3918. |
R825377 (1998) R825377 (Final) |
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Brubaker Jr. WW, Hites RA. OH reaction kinetics of polycyclic aromatic hydrocarbons and polychlorinated dibenzo-p-dioxins and dibenzofurans. Journal of Physical Chemistry A 1998;102(6):915-921. |
R825377 (1998) R825377 (Final) |
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Brubaker Jr. WW, Hites RA. OH reaction kinetics of gas-phase α-and γ-hexachlorocyclohexane and hexachlorobenzene. Environmental Science & Technology 1998;32(6):766-769. |
R825377 (1998) R825377 (Final) |
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Willett KL, Hites RA. Chemical actinometry:using o-nitrobenzaldehyde to measure lamp intensity in photochemical experiments. Journal of Chemical Education 2000;77(7):900-902. |
R825377 (1998) R825377 (Final) |
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Supplemental Keywords:
atmosphere, measurement, anthropogenic, assessment, toxic, organic, vapor phase, PCB's, toxicology, RFA, Air, Scientific Discipline, Engineering, Environmental Chemistry, Engineering, Chemistry, & Physics, tropospheric ozone, dioxin, combustion, fate, fate and transport, furans, toxicology, food chain, chemical kinetics, photodegradation, VOCs, hydroxyl radical, PCBsProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.