Grantee Research Project Results
Final Report: Remote, Real-Time Monitor for Elemental Speciation of Air Particulates
EPA Contract Number: EPD06089Title: 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: II
Project Period: April 1, 2006 through June 30, 2007
Project Amount: $224,985
RFA: Small Business Innovation Research (SBIR) - Phase II (2006) Recipients Lists
Research Category: Air Quality and Air Toxics , Particulate Matter , SBIR - Air Pollution , Small Business Innovation Research (SBIR)
Description:
The monitoring of particulate matter (PM) has long been a major research topic for EPA as it can provide important information about the sources of PM and the long-term health effects. The composition characterization of PM2.5 and PM-coarse has, to date, involved sample collection and subsequent laboratory measurements. Energy-dispersive X-ray fluorescence (EDXRF) analysis is a well-established analytical method used by the U.S. Environmental Protection Agency (EPA) for elemental speciation of PM. The particulates are collected onto large filter media at a standard mass flow rate. Long sample collection time, typically 24 hours, is needed to obtain enough materials for analysis. The primary reason for the long sample collection time is the lack of sensitivity of the conventional EDXRF analysis, which requires high-powered, complex, and expensive instruments along with a complex measurement procedure to maximize the capability of the technology. The off-site analysis results in a 24-hour or more delay in identifying air pollution hazards, identifying potential sources, and notifying the public. Furthermore, some trace hazardous metals (Pb, As, Se, Hg, Br, and Sr) are particularly difficult to detect with conventional EDXRF, and reliable data are rarely available. Field deployable EDXRF instruments for use with PM monitoring have received more attention in recent years, but the performance is compromised compared to the laboratory systems.
The primary goal of this SBIR Phase II project was to develop a high-sensitivity, optic-based EDXRF analyzer that could be either coupled with a special air sampler for continuous sample collection and analysis or used as a stand-alone instrument that could be optimized for different types of PM samples. The X-ray analyzer uses a proprietary monochromatic EDXRF method, in which the excitation X-ray beam consists of monochromatic, focused X-rays provided by an innovative doubly curved crystal (DCC) X-ray optic. The use of monochromatic excitation completely eliminates the effects of scattered bremsstrahlung radiation from the X-ray source, 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. The focused beam also allows reliable analysis to be achieved with a minimal amount of sample material, which means that sample collection time can be significantly reduced if the particles are collected in a small deposit area. The other important part of the project research was to identify appropriate air sampling technologies that will generate small PM samples with a reasonable mass flow rate. The goal was to demonstrate that the monochromatic EDXRF analyzer could detect trace contaminants, particularly heavy metals, with a 1-hour sample collection time, and that high-resolution time-resolved elemental analysis could be achieved.
Because of the advanced technologies applied, the proposed system with a compact, air-cooled 50-watt (or less) X-ray tube can achieve significantly higher detection sensitivity than the current laboratory-based EDXRF system that employs a 200-watt, water-cooled X-ray tube. The compact, low-power X-ray analyzer in the proposed system also makes it more suitable to be used for field instruments.
Summary/Accomplishments (Outputs/Outcomes):
A prototype monochromatic EDXRF analyzer that incorporates the latest development of advanced X-ray optic technologies was designed and built during the Phase II project. A variety of PM samples were analyzed. Excellent performance for PM-coarse sample analysis and for time-resolved measurements with high time resolution was demonstrated successfully. The high detection sensitivity achieved with optic-enhanced system design also allows reasonable performance to be obtained for conventional large area filter samples. Some of the major findings and conclusions are summarized below.
1. The analyzer works most efficiently with the PM-coarse samples collected by an air sampler developed by one of our collaborators. The minimal detection limit for elements such as copper, iron, nickel, and zinc was estimated to be 10-20pg/m3, and 30-60pg/m3 for lead, mercury, calcium, and sulfur. Such performance makes it possible to monitor trace metal contamination in ambient air with only 1-hour sample collection time.
2. Good detection sensitivity also was achieved for PM2.5 samples with 10mm collection area. The results agree well with those obtained with the standard XRF procedure. It was demonstrated that by improving the system configuration and optimizing the sampling configuration, the performance for large-area PM2.5 sample analysis is significantly improved.
3. The analyzer was used to measure time-resolved PM samples collected by a commercial air sampler. This is, to X-Ray Optical Systems’ (XOS) knowledge, the first time such a measurement was taken with a laboratory-based XRF system. It also was successfully demonstrated that for source assessment, 1-hour sample collection time was enough to obtain reliable analysis data.
4. The stand-alone analyzer design with flexible and optimized configuration is more user-friendly and offers greater commercialization opportunities.
Conclusions:
The research work carried out in this Phase II project successfully demonstrated that a low-powered monochromatic EDXRF analyzer is capable of detecting a wide range of elements with a much higher sensitivity than conventional EDXRF methods. Detection limits of 10 to 60 pg/m3 were achieved for Fe, Cu, Zn, Br, Sr, and Br with a 50-watt X-ray source and a simple air particulate sampler. It was estimated that detection sensitivity for PM-coarse samples was more than two orders of magnitude higher than that of conventional EDXRF methods. It also was demonstrated that the monochromatic EDXRF analyzer offers higher sensitivity even for regular large PM samples.
Some of the development work completed for the analyzer has been incorporated successfully into other commercial products offered by XOS. On the other hand, the analyzer built for the current project also has utilized many designs from existing XOS products.
A major technical challenge for future development of the proposed technology is to identify appropriate and proven air sampling technologies. The sampling technologies used in the current project were either used by or have been evaluated by EPA. Several important technical issues need to be addressed. Another key issue is quality assurance, which has been EPA’s top requirement for emerging technologies. XOS expects to develop standards for review and approval and 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 (ASTM) methods will be useful in that regard. In addition, XOS will secure UL, UL-C, CE, FCC, and other certifications necessary for commercial sale; XOS has experience in obtaining these certifications.
XOS believes that the novel monochromatic EDXRF analyzer also can be used for other applications where high detection sensitivity is needed. XOS has been aggressively pursuing such commercialization opportunities by proposing technical solutions to potential end users and Original Equipment Manufacturers (OEMs) for a variety of applications in semiconductor, microelectronics, pharmaceutical, and biological industries.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 3 publications | 1 publications in selected types | All 1 journal articles |
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Chen ZW, Gibson WM, Huang H. High definition X-ray fluorescence: principles and techniques. X-Ray Optics and Instrumentation 2008;2008:318171. |
EPD06089 (Final) |
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Supplemental Keywords:
small business, SBIR, EPA, air monitoring, particulates, real-time measurement, health risks, health hazards, energy dispersive x-ray fluorescence, EDXRF, particulate matter, PM2.5, PM10, air pollution, monitoring, ecosystem protection/environmental exposure and risk, human health, pollutants/toxics, air, scientific discipline, RFA, toxicity, chemicals, environmental engineering, environmental chemistry, monitoring/modeling, environmental monitoring, heavy metals, real time monitoring, aerosol analyzers, cardiovascular vulnerability, particulate, acute toxicity, real-time monitoring, airborne metals, X-Ray fluorescence, atmospheric particles, air pollution, atmospheric chemistry, mercury, metals, atmospheric particulate matter, atmospheric measurements, XRF, micro XRF, MXRF, monochromatic EDXRF, µ-EDXRF, X-ray analyzer, X-ray optics, doubly curved crystal, polycapillary optics, X-ray source, X-Beam, ambient particulate matter, air particulate, aerosol sampler, air sampling, elemental speciation, composition measurement, human health impact, detection sensitivity, detection limit, RFA, Scientific Discipline, Air, Ecosystem Protection/Environmental Exposure & Risk, POLLUTANTS/TOXICS, HUMAN HEALTH, particulate matter, Environmental Chemistry, Chemicals, Monitoring/Modeling, 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 I:
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.