Grantee Research Project Results
Final Report: Demonstration of a Continuous, Real-Time PM2.5 Chemical Speciation Monitor Based on an Aerosol Mass Spectrometer
EPA Contract Number: EPD04008Title: Demonstration of a Continuous, Real-Time PM2.5 Chemical Speciation Monitor Based on an Aerosol Mass Spectrometer
Investigators: Onasch, T.
Small Business: Aerodyne Research Inc.
EPA Contact: Richards, April
Phase: I
Project Period: March 1, 2004 through August 31, 2004
RFA: Small Business Innovation Research (SBIR) - Phase I (2004) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Endocrine Disruptors , Environmental Engineering , Particulate Matter , SBIR - Air and Climate , Small Business Innovation Research (SBIR) , Watersheds
Description:
The goal of this research project was to develop a low-cost, small, autonomous, quantitative PM2.5 aerosol mass and chemical speciation monitoring instrument. Aerodyne Research, Inc., has developed and tested the technology necessary to construct a simpler, smaller, less costly, autonomous prototype aerosol chemical speciation monitor (ACSM) for continuous monitoring applications based on the successful Aerodyne Aerosol Mass Spectrometer (AMS). The technological challenges presented by this research project were to demonstrate: (1) adequate sensitivity using an inexpensive quadrupole mass spectrometer, (2) effective supermicron particle sampling capabilities, and (3) quantitative collection efficiencies for ambient PM2.5 aerosol mass and chemical composition measurements.
Summary/Accomplishments (Outputs/Outcomes):
The project was accomplished through four tasks. The first task was to demonstrate effective sampling of supermicron particles. The current AMS aerosol sampling critical orifice and focusing lens was tested in the laboratory for size-dependent collection efficiency and was shown to provide a PM1.0 measurement (50% cutoff near 1,000 nm in diameter and 100% collection efficiency down to 50 nm diameter). A combination of laboratory tests and FLUENT calculations led to the design of a new aerosol sampling lens and critical orifice that effectively samples particles in the size range of 200-3,000 μm in diameter, thus enabling PM2.5 in addition to the current PM1.0 measurements with Aerodyne Research’s ACSM and AMS instruments.
The second task was to quantify particle collection efficiencies as a function of particle size, shape, and phase, in collaboration with Professor Jose Jimenez from the University of Colorado at Boulder. A particle beam width probe and a new light scattering module, both designed and built at Aerodyne Research, were employed with an AMS to analyze the dispersion and collection efficiencies of particles after they passed through the sampling orifice and focusing lens. The beam width probe measurements indicated that liquid and solid inorganic and organic particles, including propane flame soot, all strike the AMS vaporizer for the midlength chamber size (the ACSM prototype chamber is actually shorter). Thus, the fact that the standard AMS has collection efficiencies less than 100 percent for solid particles implied particle bounce problems at the vaporizer surface. This phenomenon was confirmed using an internal light scattering probe installed inside the AMS chamber, such that all particles that strike the vaporizer first pass through a laser beam and are detected optically. With the light scattering module in place, 100 percent of generated particles were detected by the optical system, but not by the mass spectrometer detector, confirming particle bounce. With this knowledge, Aerodyne Research has a new design for a vaporizer that will limit particle bounce and ensure quantitative detection with the mass spectrometer. This new vaporizer system will be built and tested for the prototype during Phase II.
The third task was to modify an existing AMS instrument to test the conceptual ACSM design. An inexpensive, small, low-power quadrupole mass spectrometer (called a Prisma) was acquired from Pfieffer Vacuum, Inc., through a no-cost purchase order agreement to test on a standard AMS chamber. The Prisma mass spectrometer was fitted to the existing chamber through an adapter flange and successfully tested with the manufacturer’s software package. By making use of the compact mass spectrometer and the included software package, overhead costs for in-house electronics and software development and support can be significantly reduced. The mechanical chopper apparatus in the modified AMS had to be rewired, and software had to be written to control the chopper (used as a masking flag) from within the Prisma software package. This masking flag was used to alternately block the particle beam, allowing for a background mass spectrum and allowing the particle beam to pass, giving a mass spectrum of the particles plus vacuum chamber background. Data analysis routines were developed to obtain the different spectra from the sample and background spectra.
The final task, carried out in collaboration with Dr. Karsten Baumann at the Georgia Institute of Technology, was to compare measurements taken with a standard AMS, the modified Prisma AMS, and filter-based PM2.5 particulate mass and chemical speciation methods (Federal Reference Method and Particle Composition Monitor) for quantifying ambient aerosol. The results from these comparison tests indicate that the modified AMS is quantitative and has the necessary sensitivity and time response to be of value to the aerosol monitoring community.
Conclusions:
The technology developed and proven in Phase I indicates that Aerodyne Research is capable of producing an ACSM instrument that measures nonrefractory submicron PM2.5 ambient aerosol mass and chemical composition in real time, providing quantitative measurements of particulate ammonium, nitrate, sulfate, chloride, and organic mass. The ACSM will be designed to run autonomously for extended periods of time and will require no expensive postprocessing analysis. The ACSM will be a simple, robust, modestly priced aerosol chemical speciation instrument ideal for the regulatory monitoring market. The design for this new instrument comes from a lengthy history of developing successful research-grade AMS instruments and the experience obtained from quantifying particle collection efficiencies; migrating from a PM1.0 to a PM2.5 measurement; successfully integrating a small, self-contained, low-resolution mass spectrometer onto a standard AMS chamber; and showing that the modified system has the sensitivity and selectivity to provide relevant and accurate nonrefractory aerosol mass and chemical composition information for typical ambient aerosol loadings.
During Phase II, a full prototype ACSM instrument will be constructed, including the newly designed vaporizer, sampling orifice, and focusing lens systems. This prototype ACSM will be subsequently tested in the field along side standard AMS and U.S. Environmental Protection Agency-approved filter-based methods. With successful completion of the construction and testing of the prototype instrument, the goal of producing a low-cost (approximately $130,000), small (about 100 lbs), autonomous, quantitative PM2.5 aerosol mass and chemical speciation monitoring instrument will be achieved. The final step is to use the technologies developed for the AMS research-grade instruments to implement a dual chopper module that could be installed within the ACSM to enable size-dependent chemical speciation measurements. This will be pursued as an option to the Phase II research project.
Supplemental Keywords:
small business, SBIR, EPA, chemical speciation monitor, aerosol mass spectrometer, AMS, particulate matter, PM2.5, PM 10, aerosol chemical speciation monitor, real time, ACSM, particle collection, light scattering module, vaporizer, monitoring, SBIR,, RFA, Scientific Discipline, Air, Ecosystem Protection/Environmental Exposure & Risk, RESEARCH, particulate matter, Air Quality, Environmental Chemistry, Monitoring/Modeling, Analytical Chemistry, Monitoring, Environmental Monitoring, Atmospheric Sciences, particle size, atmospheric measurements, aerosol mass spectrometer, chemical characteristics, human health effects, air quality models, monitoring stations, gas chromatography, air quality model, air sampling, modeling, particulate matter mass, particle sampler, human exposure, continuous emissions monitoring, modeling studies, aerosol analyzers, atmospheric chemistrySBIR Phase II:
Demonstration of a Continuous, Real-Time PM2.5 Chemical Speciation Monitor Based on an Aerosol Mass Spectrometer | 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.