Grantee Research Project Results
1997 Progress Report: Real-Time Trace Detection of Elemental Mercury and its Compounds
EPA Grant Number: R825380Title: Real-Time Trace Detection of Elemental Mercury and its Compounds
Investigators: Barat, Robert
Institution: New Jersey Institute of Technology
EPA Project Officer: Hahn, Intaek
Project Period: November 25, 1996 through November 24, 1998
Project Period Covered by this Report: November 25, 1996 through November 24, 1997
Project Amount: $199,121
RFA: Analytical and Monitoring Methods (1996) RFA Text | Recipients Lists
Research Category: Environmental Statistics , Water , Land and Waste Management , Air , Ecological Indicators/Assessment/Restoration
Objective:
The current research program has three major technical objectives: 1) Design and fabricate a versatile supersonic jet fluorescence spectrometer; 2) Test the effectiveness of Doppler-shifted atomic resonance fluorescence for measuring low concentrations of elemental mercury vapor (at sub-parts per billion concentration); and, 3) Test the effectiveness of photo-fragmentation fluorescence spectroscopy (PFFS) for speciating mercury compounds at low concentration.This program will determine the capabilities and limitations of mercury detection in real-time by the proposed techniques. It is anticipated that the detection limits for elemental mercury will be on the order of 0.1 microgram/cubic meter. It is desirable that response be linear up to about 5000 microgram/cubic meter. It is anticipated that PFF signals will successfully discriminate between species such as mercuric chloride and chloromethyl mercury at detection levels below 1 microgram/cubic meter.
Progress Summary:
The vacuum chamber and supersonic jet assembly are completed. Chamber optical access is complete. The UV light beam has been directed into the chamber to intersect the jet. The jet is being imaged with a visibly fluorescing tracer to ensure good light beam - expanding jet interaction. Collection optics and light detection devices are available. Sources for producing gas streams containing elemental mercury or compound mercury have been fabricated. Photo-fragmentation fluorescence experiments in a separate, atmospheric pressure flow cell with mercuric bromide in argon are being used to estimate limits of detection. Analysis of the PFF signal has suggested that time gating of the collected light signal might allow for extraction of the mercury PFF signal from the prompt scattering background.Accomplishments and Research Results
Test gas is expanded into a vacuum chamber in a supersonic jet. Within the chamber, the jet is intersected by a deep ultraviolet (UV) light beam. Fluorescence is collected within the chamber and directed out for processing and detection.
The vacuum chamber with expansion jet has been assembled. Vacuum is provided by an oil diffusion + mechanical roughing pump train. A liquid nitrogen trap is in place downstream of the chamber to capture mercury species. A subambient temperature reservoir has been designed and constructed to allow air to pass over elemental mercury and become saturated with its vapor. A heated source for mercury compound vapor-in-air has also been constructed and tested. Each setup will serve as the sources for the jet. Mercury species concentration in air (or other gas) will be controlled by adjusting the source temperature (species vapor pressure).
The optical system is effectively assembled. Vacuum chamber optical access through quartz windows has been achieved. An optical rail has been mounted in the chamber to hold components. Steering optics direct a UV laser beam into the chamber through one window and perpendicular to the expanding jet. Emitted light is collected by an off-axis parabolic reflector, and directed out through another window. The fluorescence is turned and focused onto a detector. A monochromator + photomultiplier tube combination detector is available. It is interfaced to a boxcar / gated integrator. A computer- interfaced CCD detector array is also available.
In order to assure that the incoming UV beam insects the jet, the jet will be imaged by seeding the gas (e.g. argon, air) flow with elemental iodine, and exciting visible fluorescence (yellow) with green laser light (532 nanometer). Preliminary experiments with iodine crystals in a closed quartz cell have confirmed this emission.
Work has continued on a complementary experiment which is providing insight for the jet experiment. An atmospheric pressure flow cell with optical access has been used to gather data on PFFS of mercuric bromide in argon. Important support data on issues such as source and transfer line temperature control, time gating during signal detection, and signal/concentration linearity have been collected.
Future Activities:
In the coming year, several activities will be performed or completed. The expanding jet will be imaged with 532 nm green laser light. Mercury compound will be introduced into the chamber for PFFS experiments using a UV laser beam. Mercuric bromide will be used since it will provide a ready comparison to the atmospheric pressure flow cell data to gauge the benefits of the jet expansion. A limit of detection will be estimated. Elemental mercury will then be used. Time gating will be attempted to minimize the impact of background scatter. If necessary to boost the recovered resonant fluorescence signal, a static mercury vapor cell will be used to take advantage of the Doppler shift of the atomic fluorescence.Journal Articles:
No journal articles submitted with this report: View all 4 publications for this projectSupplemental Keywords:
Scientific Discipline, Water, Ecosystem Protection/Environmental Exposure & Risk, Environmental Chemistry, Monitoring/Modeling, Environmental Monitoring, Engineering, Mercury, resonant flourescence, ambient particle properties, industrial waste, doppler shifting, air pollution, elemental mercury, high vapor pressure, waste combustion, aerosol analyzers, air quality, metalsProgress 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.