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INVESTIGATING THE INFLUENCE OF LONG RANGE TRANSPORT ON MERCURY DEPOSITION IN SOUTH FLORIDA
Citation:
Landis, M S., R. K. STEVENS, W. Luke, AND G. J. Keeler. INVESTIGATING THE INFLUENCE OF LONG RANGE TRANSPORT ON MERCURY DEPOSITION IN SOUTH FLORIDA. Presented at 6th International Conference on Mercury as a Global Pollutant, Minamata, Japan, October 15-19, 2001.
Impact/Purpose:
The overall research objective of this task is to improve our understanding of the emission, transport, transformation, and deposition of atmospheric mercury. Information garnered from this research is used to improve and evaluate EPA deterministic models that are used to investigate the (i) relative impact to local, regional, and global sources to atmospheric mercury deposition, and (ii) benefits of various emission reduction scenarios.
Specifically, individual research project objectives are listed below:
(1) Evaluate the ability of speciated mercury (Hg0, Hg2+, HgP) measurements to aid source apportionment models in identifying anthropogenic source contributions to atmospheric mercury deposition
(2) Elucidate the contribution of coal combustion sources to observed mercury wet deposition in the Ohio River Valley
(3) Obtain atmospheric profiles (200 - 12,000 ft) of speciated ambient mercury off the south Florida Coast
- Evaluate the role of long range transport of RGM to Florida in the marine free troposphere.
- Identify any vertical mercury gradients that might indicate the presence of rapid mercury chemistry in air or in cloud water.
(4) Conduct research at Mauna Loa Observatory to elucidate elemental mercury oxidation in the remote marine free troposphere.
(5) Conduct laboratory kinetics experiments to determine the rate constants of elemental mercury oxidation to gaseous inorganic divalent mercury species from atmospheric halide species (e.g. BrO, ClO).
Description:
In 1999, the US EPA National Exposure Research Laboratory (NERL) through a Regional Applied Research Effort initiated a study to evaluate the magnitude of long-range transport of mercury through the marine free troposphere to South Florida via aircraft measurements (200 to 11,500 feet). NERL funded the National Oceanic and Atmospheric Administration Air Resources Laboratory (ARL) to provide a DeHavilland Twin Otter aircraft and personnel to collaborate with the collection of aerosol and trace gas measurements. A heated Teflon-coated aluminum inlet system with a quazi-isokinetic decelerator jet tip was installed in the aircraft to direct an air stream into a manifold where elemental gas phase mercury (Hg0), reactive gaseous mercury (Hg2+), particulate phase mercury, and trace element aerosols were collected by NERL. In addition, ARL collected real time measurements of ozone, carbon monoxide, sulfur dioxide, nitrogen oxides (NO, NOx, NOy), and condensation nuclei.
Two separate study periods of 50 flight hours were planned. The first study period was conducted from January 18, through February 1, 2000 when the tropospheric winds typically transport air to South Florida from the Gulf of Mexico and the North American continent. Flights for the second study period were conducted from June 3 through June 26, 2000 when South Florida is predominantly influenced from easterly marine transport. Preliminary results from the flights indicate that mercury concentrations were significantly higher within air masses with continental influence. The Hg0 concentrations were observed to be higher below 5000 feet (2.3 +/- 0.4 ng m-3) than above 5000 feet (1.5 +/- 0.4 ng m-3). Conversely, the concentrations of Hg2+ were typically higher above 5000 feet (49 +/- 28 pg m-3) than below (12 +/- 7 pg m-3). Meteorological modeling and chemical tracer results will be presented.
This work has been funded wholly or in part by the United States Environmental Protection Agency Office of Research and Development. It has been subjected to peer review and approved for publication.