  Privacy
| Legal |
Table of Contents Back | Next | Home | Cover Page |
 Technology & Development Center |
Real-Time
Smoke
Particulate Sampling
Fire Storm 2000
Radiance Research Nephelometer
The Radiance Research nephelometer, M903 (figure 12) is a lightweight, low-power instrument designed for portable operation as well as general environmental monitoring. The M903 measures and displays the back- scattering coefficient. It does not display a computed estimate of mass concentration, as do the other nephelometers in the evaluation. Mass concentrations can be estimated from the back-scattering readings. The instrument has a particulate measurement range of about 1 to 1,000 µg/m³ when mass concentration is estimated from back scattering. The instrument has an internal data logger that will store scattering coefficient averages and the operating parameters that are used to estimate the back scattering. The stored data can be retrieved using a personal computer through an RS-232 port. Different averaging times and log intervals may be set. The instrument can store about 2 weeks of 5-minute averages. An external span gas, such as Freon, is required for calibration. The unit can be powered by an ac or dc power source.
Figure 12—The Radiance Research M903
nephelometer (with attached inlet heater).
Andersen RTAA 900 Aethalometer
The Andersen RTAA 900 aethalometer (figure 13) measures suspended carbonaceous particulates. Aerosol black carbon (BC) is a ubiquitous component of combustion emissions. The aethalometer uses a continuous filtration and optical transmission technique to measure the concentration of BC in near real time. The model RTAA 900 is a dual wavelength system that measures both the BC at 800 nm (nanometers) and the UV (ultraviolet) at 325 nm.
Figure 13—The Andersen RTAA 900 aethalometer.
The aethalometer is fully automatic and completely self-contained. It is constructed in a standard 19-in enclosed chassis and includes a filtration and analysis chamber with an automatically advancing quartz fiber tape, a sample aspiration pump and air mass flow meter or controller (typical flow rates are 2 to 6 L/min), and temperature-stabilized optics and electronics. The instrument is operated by an embedded computer with display screen and keypad that controls all instrument functions and records the data to a built-in 3.5-in floppy diskette. The instrument has a communications (COM) port for digital data stream output and an analog voltage terminal that can be programmed to represent the measured concentrations or to function as an on/off threshold alarm.
One method of determining particulate mass concentrations in real time uses a TEOM instrument. Particulate is continuously collected on a filter mounted on the tip of a glass element that oscillates in an electric field. The glass element is hollow, with the wider end fixed. Air is drawn through the filter and through the element. The oscillation of the glass element is maintained based on the feedback signal from an optical sensor. The resonant frequency of the element decreases as mass accumulates on the filter, directly measuring inertial mass. Temperatures should be maintained at a constant value to minimize thermal expansion of the tapered element.
Rupprecht & Patashnick Co., Inc., (figure 14) manufactures a TEOM ambient particulate monitor, Model 1400a. This monitor is designated by the EPA as an equivalent method PM10 monitor. It incorporates an inertial balance that directly measures the mass collected on an exchangeable filter cartridge by monitoring the corresponding frequency changes of the tapered element. Typical averaging times are 1 h. These monitors are deployed worldwide, including one in Missoula, MT, operated by the MT DEQ. The instrument can be configured for PM10, PM2.5, PM1 or total suspended particulate (TSP). The instrument has internal data logging storage for 40 weeks of data with one variable stored every hour. Data can be downloaded using an RS-232 port. The instrument also has three real-time analog outputs. The Rupprecht & Patashnick TEOM is very large and heavy (52 in high by 47 in wide by 24 in deep, weighing 180 lb, in its environmental enclosure) compared to the optical, real-time continuous samplers and is usually a more permanent installation.
Figure 14—The Rupprecht & Patashnick tapered
element oscillating microbalance instrument.
 |
E-mail: