Grantee Research Project Results
Final Report: Remote, Real-Time Monitor for Elemental Speciation of Air Particulates
EPA Contract Number: EPD05045Title: Remote, Real-Time Monitor for Elemental Speciation of Air Particulates
Investigators: Gao, Ning
Small Business: X-Ray Optical Systems, Inc.
EPA Contact: Richards, April
Phase: I
Project Period: March 1, 2005 through August 31, 2005
Project Amount: $69,922
RFA: Small Business Innovation Research (SBIR) - Phase I (2005) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Endocrine Disruptors , Environmental Engineering , SBIR - Air and Climate , Small Business Innovation Research (SBIR) , Watersheds
Description:
The primary goal of this research project was to demonstrate the feasibility of developing a compact and field-deployable ambient aerosol monitoring system that can continuously collect aerosol samples and measure the compositions in a near real-time operation mode (with a time resolution of 1 to a few hours). The system combines a compact, highly sensitive X-ray analyzer and an automatic sampling device that concentrates particulate matter (PM) to a small area for composition analysis. The X-ray analyzer uses a unique monochromatic energy dispersive X-ray fluorescence spectrometry (EDXRF) method, in which the excitation X-ray beam consists of monochromatic, focused X rays provided by an innovative X-ray optic—a doubly curved crystal (DCC) optic. Using monochromatic excitation for EDXRF analysis will completely eliminate the scattering of bremsstrahlung radiation, which is the main limiting factor of the detection sensitivity of conventional EDXRF analysis. As a result, the signal-to-noise ratio with monochromatic EDXRF is typically one to two orders of magnitude higher than that of conventional EDXRF. The use of concentrated samples will allow air particulates to be collected with higher area density and make the best use of the focused excitation beam. Because of the advanced technologies applied, the proposed system with a compact, air-cooled 50 W (or less) X-ray tube will achieve significantly higher detection sensitivity than the current laboratory EDXRF system that employs a 200 W, water-cooled X-ray tube. The compact, low-power X-ray analyzer also makes it more suitable for use as a field instrument.
Summary/Accomplishments (Outputs/Outcomes):
A compact, low-power monochromatic EDXRF analyzer was constructed during Phase I. It then was coupled with a simple aerosol-sampling device to perform real-time measurement of elemental concentrations of air particulates. A detection limit of 10-40 pg/m 3 was achieved for Fe, Cu, Zn, Br, Sr, and Br with a 50 W X-ray source. A head-to-head comparison with the conventional EDXRF method (broadband excitation and pinhole collimator) was made by setting up a conventional EDXRF system in X-Ray Optical Systems, Inc.’s laboratory. For the small aerosol samples collected through the current project, the detection sensitivity of the monochromatic EDXRF analyzer was so much higher that it was impossible to carry out quantitative analysis because most peaks from selected elements did not show up with the conventional EDXRF method. A rough estimate indicated that the detection limit of the monochromatic EDXRF was at least three orders of magnitude higher.
The performance of this approach (monochromatic EDXRF combined with small samples) then was compared with a more practical approach (i.e., conventional EDXRF with large samples). In this case, the detection limit of monochromatic EDXRF for the element Zn was 30 times lower than the conventional method. This is the most convincing evidence to date of the significant improvement of sensitivity of the proposed technology.
Even for large samples, which are not as suitable for the proposed X-ray analyzer, the detection sensitivity is approximately one order of magnitude higher than conventional EDXRF. This highlights an opportunity for using the monochromatic EDXRF method to achieve higher sensitivity for regular aerosol samples.
Several aerosol monitoring instrument manufacturers have developed continuous aerosol samplers for PM 10, PM 2.5, and PM 2.5-10; some of these manufacturers also have developed or are researching sampling techniques that will focus air particulates to smaller area. X-Ray Optical Systems, Inc., has identified potential strategic partners to pursue the improved sampling technology and combine it with the monochromatic EDXRF analyzer. The successful implementation of these new technologies will allow real-time elemental speciation of air particulates of any sizes with unprecedented sensitivity. There also is the potential to combine the mass measurement with the elemental speciation to perform simultaneous mass and elemental speciation monitoring for selected particulate sizes.
Conclusions:
The research carried out in Phase I has successfully demonstrated that a low-powered monochromatic EDXRF analyzer was capable of detecting a wide range of elements with a much higher sensitivity than the conventional EDXRF method. A detection limit of 10-40 pg/m 3 was achieved for Fe, Cu, Zn, Br, Sr, and Br with a 50 W X-ray source and a simple air particulate sampler. It was estimated that this sensitivity was more than two orders of magnitude higher than that of the conventional EDXRF method. The system’s performance can be further enhanced with a high-volume air sampler, which will be developed if the project proceeds into Phase II. X-Ray Optical Systems, Inc., also demonstrated that the monochromatic EDXRF analyzer offers significantly higher sensitivity for large PM samples.
The major challenges for future development of the technology include, but are not limited to, the addition of size-fractioning capability, high-volume sample collection with proper sampling size reduction, optimization of sample collection and analysis times, and system design for ease of use and reliable operation. Another important issue to be addressed is quality assurance, which has been the U.S. Environmental Protection Agency’s (EPA) top requirement for emerging technologies. X-Ray Optical Systems, Inc., expects to develop standards for review and approval as well as standard operating procedures to accompany the deployment of new instrumentation. This may include modification to EPA Compendium Method IO-3.3 (Determination of Metals in Ambient Particulate Matter Using XRF Spectroscopy) or other documents. The company’s experience with American Society for Testing and Materials methods will be useful in that regard. In addition, X-Ray Optical Systems, Inc., will secure UL, UL-C, CE, FCC, and other certifications necessary for commercial sale (the company has experience in obtaining these certifications).
X-Ray Optical Systems, Inc., also believes that the novel monochromatic EDXRF analyzer can be used for other applications in which high detection sensitivity is needed. The company has been aggressively pursuing such commercialization opportunities by proposing technical solutions to potential end users and original equipment manufacturers for a variety applications in semiconductor, microelectronics, pharmaceutical, and biological industries.
Supplemental Keywords:
real-time monitor, elemental speciation, air, particulates, particulate matter, PM, monochromatic energy dispersive X-ray fluorescence spectrometry, EDXRF, X-ray optics, doubly curved crystal, DCC, air sampling, air pollution, real-time monitoring, EPA, small business, SBIR,, RFA, Scientific Discipline, Air, Ecosystem Protection/Environmental Exposure & Risk, POLLUTANTS/TOXICS, HUMAN HEALTH, particulate matter, Environmental Chemistry, Chemicals, Monitoring/Modeling, Analytical Chemistry, Toxicity, Environmental Monitoring, Environmental Engineering, atmospheric particulate matter, atmospheric measurements, atmospheric particles, mercury, particulate, airborne particulate matter, cardiovascular vulnerability, air pollution, airborne metals, acute toxicity, real time monitoring, X-Ray flourescence, metals, aerosol analyzers, atmospheric chemistry, heavy metalsSBIR Phase II:
Remote, Real-Time Monitor for Elemental Speciation of Air Particulates | Final ReportThe 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.