0325-2834-MTDC, Laboratory Evaluation of Real-Time Smoke Particulate Monitors: Laboratory Tests

Since 2000, several new or improved real-time particulate samplers have become commercially available. MTDC was asked to conduct laboratory tests to compare the new samplers with the FRM sampler to determine the accuracy of the new instruments when estimating smoke particulate concentrations. As in the previous laboratory tests, we set up the instruments side by side on the elevated platform at the Fire Sciences Laboratory’s smoke chamber platform and burned pine needles to generate smoke particulate. Filters used in the FRM gravimetric instrument were weighed by the Montana Department of Environmental Quality.

Real-Time Instruments

Three new or improved real-time instruments were tested. Two were new instruments developed by MetOne Instruments, Inc. The other was an improved version of an instrument we had tested previously, the MIE DataRAM4. MetOne Instruments manufactures the BAM 1020, an EPA-approved equivalent method PM₁₀ real-time particulate sampler that uses beta attenuation to estimate particulate concentrations. The instrument can be configured with a PM_2.5 cutoff device to estimate PM_2.5 concentrations. The instrument was not developed as, nor was it intended to be, a portable device. MetOne developed the portable E-BAM (figures 2 and 3), a smaller version of the BAM 1020, which uses the same technology to estimate mass concentrations. MetOne also developed a new instrument called the E-Sampler for estimating real-time concentrations. The E-Sampler uses light-scattering principles to estimate mass concentrations. The MIE DataRAM4 is similar to the DataRAM 2000, which we tested previously, but the DataRAM4 includes a second optical wavelength to increase accuracy.

[photo] MetOne Instruments' E-Bam monitor

Figure 2—MetOne Instruments’ E-BAM monitor is a portable real-time beta-attenuation PM2.5 and PM10 particulate monitor.

[photo] E-Bam monitor with environmental door open

Figure 3—The E-BAM monitor with its environmental door open. The instrument collects particulate on a filter tape that automatically advances when the tape is full.

E-BAM—MetOne Instruments’ E-BAM (the E stands for environmentally protected) monitor uses a three-part process to estimate mass concentrations. First, beta particles from a naturally occurring radioactive isotope are emitted through a filter tape and counted. Second, sampled air is passed through the filter paper and particles are deposited. Finally, beta particles are again passed through the paper and recounted. The second count will be lower than the first, because beta particles will have been absorbed by the deposited particulate. Calculations can determine the mass of the deposited particulate. The mass is divided by the amount of sampled air to calculate the concentration in mass per unit volume. When the filter paper reaches a predetermined concentration, the paper will automatically advance and begin a new collection.

The E-BAM monitor is a portable instrument that can operate in hostile environments without the need for an additional enclosure. It can operate using line (110 volts AC), battery, or solar power. It can be configured with EPA-approved PM₁₀ and PM_2.5 cutoff devices to remove particulate larger than PM₁₀ or PM_2.5, respectively. It uses pressure and ambient temperature sensors to measure airflow accurately. The E-BAM monitor can be mounted on a tripod and configured to accept a variety of ambient monitoring sensors like windspeed and direction, relative humidity, and temperature. A six-channel data logger stores all the information. The range of measured concentration is 0 to 100 milligrams per cubic meter. The data logger can be programmed to report as often as every minute. Data can be downloaded using an RS-232 serial port. A laptop computer or a modem can be configured to transmit the data using telephone lines, cell phone connections, or satellite telemetry.

The E-BAM measures 16 inches high by 13½ inches wide by 8 inches deep. It weighs about 28 pounds without the PM₁₀ and PM_2.5 inlets. The inlets weigh an additional 7.5 pounds and add 30 inches to the height when they are installed. A power supply to operate the instrument off 110-volt AC line power weighs 14 pounds.

More information can be found at MetOne Instruments’ Web site at http://www.metone.com or by calling 541–471–7111.

MetOne Instruments’ E-Sampler—The MetOne Instruments E-Sampler (figure 4) uses light-scattering principles to estimate mass concentrations of airborne particulate. An internal visible laser diode is focused and directed through the sample air. When particulate-laden sample air intersects the laser beam, a portion of the light is scattered. The scattered light is collected at a near forward angle and focused on a photodiode that converts the light to an electrical signal. The signal strength is proportional to the amount of scattered light. An algorithm converts the electrical signal to mass concentration.

[photo] MetOne Insturments' E-Sampler
Figure 4—MetOne Instruments’ E-Sampler uses light-scattering
principles to estimate particulate concentrations.

The E-Sampler is a small, lightweight instrument housed in an environmentally protected enclosure. It can estimate particulate concentrations up to 100 milligrams per cubic meter. It can be configured for total suspended particulate (TSP), PM₁₀, PM_2.5, and PM₁, using a cutoff device. The E-Sampler can be mounted on a tripod and operated using line, solar, or battery power. A six-channel data logger accommodates other meteorological sensors such as windspeed and direction, relative humidity, and ambient temperature. The sampler also has an inlet heater that can be programmed to operate when the inlet airflow’s relative humidity reaches a particular level. Humidity can cause the instrument to overestimate particulate concentrations. The heater removes moisture from the air before it is sampled.

The E-Sampler is considered a dual technology instrument. Besides the real-time optical scattering measurement, the E-Sampler also incorporates a gravimetric filter system using the same 47-millimeter filters as the FRM sampler. The results from the gravimetric device can be used to improve the accuracy of the real-time estimations.

The E-Sampler is compact, 10 inches wide by 12 inches high by 5 inches deep. It weighs 13 pounds with the PM_2.5 inlet, heater, and power supply.

More information can be found by visiting MetOne Instruments’ Web site at: http://www.metone.com or by calling 541–471–7111.

MIE DataRAM4—The MIE DataRAM4 (figure 5) is an upgraded version of the DataRAM 2000, which we tested from 1998 to 2000. The DataRAM4 uses light-scattering principles to estimate mass concentrations. However, the DataRAM4 has dual light sources at different wavelengths (600 and 880 nanometers). In theory, this dual wavelength allows the DataRAM4 to better estimate mass concentrations based on an algorithm from the scattering signals from each light source. The algorithm uses the mean particle diameter size computed from the light scattering to correct the mass concentrations.

[photo] MIE DataRam4
Figure 5—The Thermo-Electron MIE DataRAM4
(shown with satellite telemetry system) is a dual-wavelength,
light-scattering device that estimates particulate concentrations.

Some of the new features of the DataRAM4 include internal temperature and relative humidity sensors, the ability to autocorrect concentrations when measuring air at high relative humidities, and the ability to measure mean particle diameter size. It can measure particulate concentrations up to 400 milligrams per cubic meter and has a built-in data logger to store up to 50,000 data points. Like the E-Sampler, the DataRAM4 has a built-in gravimetric filter system for custom calibrations, although it uses a 37-millimeter membrane filter that is smaller than the 47-millimeter filter used in the FRM sampler.

The DataRAM4 monitor is 5.3 inches high by 7.3 inches wide by 13.6 inches long and weighs 11.7 pounds.

More information on the MIE DataRAM4 can be found at: http://www.thermo.com or by calling 1–800–241–6898.

Laboratory Tests of Real-Time Particulate Samplers

Real-Time Instruments