Grantee Research Project Results
Final Report: An Innovative Sampler as a Reference Standard for Measurement of Particulate Matter Mass in Ambient Air
EPA Contract Number: 68D03047Title: An Innovative Sampler as a Reference Standard for Measurement of Particulate Matter Mass in Ambient Air
Investigators: Ambs, Jeffrey
Small Business: Rupprecht & Patashnick Co, Inc.
EPA Contact: Richards, April
Phase: II
Project Period: May 1, 2003 through April 30, 2004
Project Amount: $224,993
RFA: Small Business Innovation Research (SBIR) - Phase II (2002) Recipients Lists
Research Category: Ecological Indicators/Assessment/Restoration , SBIR - Monitoring , Small Business Innovation Research (SBIR)
Description:
Rupprecht & Patashnick Co., Inc., has developed an innovative continuous monitor designed as a reference standard for particulate matter (PM) mass measurements in ambient air. Differential Tapered Element Oscillating Microbalance (TEOM®) monitors were evaluated at different test locations and over multiple seasons to verify that the devices properly account for the mass of semivolatile materials that are present in the atmosphere at the time of sample collection. Both an electrostatic precipitator (ESP) based version and a filter-based version were evaluated. The ESP-based Differential TEOM monitor and the Filter Dynamics Measurement System (FDMS) were compared to results collected using the current Federal Reference Method (FRM) and with the Particle Concentrator-Brigham Young University Organic Sampling System (PC-BOSS) and Real-Time Ambient Mass (RAMS) samplers, which were designed specifically to measure the total PM mass, including the semivolatile material. Because the FRM is susceptible to artifacts in the sample caused by the loss of semivolatile material from the filter during sampling, FRM measurements do not necessarily provide accurate representations of ambient PM mass. The Differential TEOM monitor was developed to properly account for these artifacts while also providing real-time ambient PM mass measurements.
Summary/Accomplishments (Outputs/Outcomes):
Collocated Differential TEOM monitors, both ESP-based and FDMS units, were evaluated in Rubidoux, CA; Bakersfield, CA; Fresno, CA; and Atlanta, GA, over multiple seasons. Comparisons between the Differential TEOM monitors showed high precision in the results and excellent intercomparisons between the two types of Differential TEOM monitors. The Differential TEOM monitors also were operated at different control temperatures, including ambient temperature, to determine the effect of sample temperature on the collection and measurement of semivolatile compounds. The data show that the Differential TEOM monitor results are unaffected by the operating temperature of the monitor.
The ability of the Differential TEOM monitors to properly measure ambient PM mass under all conditions, including under circumstances of high levels of semivolatile material in the atmosphere, was evaluated. In comparing the results with those collected using PC-BOSS and RAMS samplers in addition to speciation-specific measurements, it is clear that the ESP Differential TEOM monitor and FDMS properly account for the known levels of semivolatile material, including ammonium nitrate and semivolatile organics. Data show that during periods of high semivolatile material levels, the Differential TEOM monitors can be used to identify these episodes through the ability of the monitors to measure and report the effect of the semivolatile mass on the base mass measurement.
The results of the Differential TEOM monitors were compared with FRM samples collected in Rubidoux and Bakersfield. Sample artifacts, which continuously are occurring during the sampling ambient PM, including on FRM samples, result in the FRM underreporting the level of ambient PM mass, especially in areas where the compositions of semivolatile materials were significant. These artifacts are corrected for with the Differential TEOM monitor to provide a proper measurement of the ambient PM mass.
Conclusions:
The Differential TEOM monitor concept was developed to provide an instrument that could serve as the reference standard for atmospheric PM mass measurements. In one form of the instrument, an ESP is used to periodically remove the particles from the sample gas before they can be collected on the sample filter. During the periods when the ESP is off, the mass sensor collects and measures the mass concentration of the sample, as with a standard TEOM Series 1400a Ambient Particulate Monitor. In addition to measuring the actual PM mass, this base mass also measures any artifacts of the measurement process, such as the adsorption of gases, evaporation of previously collected semivolatile material, temperature effects, etc. These artifacts continuously are occurring on all types of samples of ambient PM, including FRM samples and beta attenuation monitor measurements. These artifacts need to be accounted for in the measurement to provide a proper measurement of the ambient PM mass. With the Differential TEOM monitor, this is accomplished by periodically removing the incoming particluates from the sample gases, either through the use of an ESP (ESP Differential TEOM monitor) or with a chilled filter (FDMS). Because the particles are removed, any change in the mass on the TEOM monitor sample filter is the result of the artifacts that occur continuously in ambient PM sampling. This reference mass measurement is subtracted from the base mass measurement and results in the net, or actual, ambient PM mass concentration.
Ideally, the mass collection and measurement is performed at the same temperature as the ambient particles; however, as demonstrated in this report, it is not necessary to perform this sampling and measurement at ambient temperature. The only requirement is that cycle time between the periods when the particles are sampled and removed from the sample gas be short enough such that the effect of the artifacts occur over a time period longer than the cycle time. The experiments that were performed illustrate that a cycle time of 5 minutes is long enough to provide reasonable signal-to-noise levels, and at the same time is short enough that the sampling artifacts occur over more than one switch cycle, even at a sampling temperature of 50°C.
The ability of the Differential TEOM monitor (both ESP-based and the FDMS) to properly measure ambient PM mass under all conditions, including under circumstances of high levels of semivolatile material in the atmosphere, was evaluated. Comparing the results with those collected using the PC-BOSS and RAMS, two research instruments developed at Brigham Young University, and with individual speciation measurements, such as continuous nitrate and continuous carbon measurements, it is clear that the Differential TEOM monitor and FDMS properly account for the known levels of semivolatile material. Data show that during periods of high semivolatile material levels, the Differential TEOM monitors can be used to identify these episodes through the ability of the monitors to report the reference mass concentrations measured. The differential technique as implemented through either the ESP Differential TEOM monitor or the FDMS can be considered a reference standard for ambient PM mass measurements.
Supplemental Keywords:
sampler, reference standard, particulate matter, PM, ambient air, Differential Tapered Element Oscillating Microbalance monitor, TEOM monitor, electrostatic precipitator, ESP, Filter Dynamics Measurement System, FDMS, Federal Reference Method, FRM, Particle Concentrator-Brigham Young University Organic Sampling System, PC-BOSS, Real-Time Ambient Mass, RAMS, semivolatile material, TEOM Series 1400a Ambient Particulate Monitor, small business, SBIR., RFA, Scientific Discipline, Air, Ecosystem Protection/Environmental Exposure & Risk, particulate matter, Monitoring/Modeling, Analytical Chemistry, Environmental Monitoring, Atmospheric Sciences, Ecology and Ecosystems, ambient aerosol, asthma, atmospheric measurements, semi-volatile organic material, ambient particle properties, environmental measurement, ambient measurement methods, air sampling, aerosol composition, electrostatic precipitator, particulate matter mass, aersol particles, semi-volatile particulate speciesSBIR Phase I:
Innovative Sampler as a Reference Standard for Measurement of Particulate Matter Mass in Ambient Air | 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.