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Evaluation of Optical Instruments for Real-Time Continuous Monitoring of Smoke Particulates

Conclusions

The instruments had substantial differences in their measurement performance. Our data were collected in four distinct experiments, two in a smoke chamber, where a handful of pine needles were burned in a flaming and smoldering state, and two in ambient conditions near open forest fires. One indoor test and the two outdoor tests were conducted when the particle concentrations in the vicinity of the samplers were relatively low (less than about 150 µg/m³). In the other indoor experiment, concentrations reached almost 500 µg/m³. Some of the low-concentration indoor tests were conducted while the relative humidity (RH) was raised above 70 percent. The high-humidity tests were intended to evaluate two aspects of particle sampling; one was to show the relative difference in concentration using optical devices when the humidity was high and when it was low; the other was to compare the response of identical instruments when they were tested with and without a heater.

When the instruments were tested in a smoke chamber and exposed to moderately high particle concentrations (similar to those experienced by firefighters) their approximate performance was:

• MET One GT-640—Unavailable.
• MIE DataRam—Overestimated by about 93 percent.
• Radiance Research—Overestimated by about 85 percent.
• Optec NGN-3—Unavailable.
• Andersen aethalometer—Unavailable.

At lower particle concentrations (closer to the ambient air-quality standards and at levels where visibility is noticeably impaired) the instruments' approximate performance was:

• MET One GT-640—Underestimated by about 53 percent.
• MIE DataRam—Underestimated by about 25 percent.
• Radiance Research—Overestimated by about 13 percent.
• Optec NGN-3—Underestimated by 10 to 32 percent.
• Andersen aethalometer—Unavailable.

During field tests when particle concentrations were close to the ambient air-quality standards and at levels where visibility is noticeably impaired, the instruments' approximate performance was:

• MET One GT-640—Overestimated by about 10 percent, but data were scattered.
• MIE DataRam—Overestimated by about 21 percent.
• Radiance Research—Overestimated by about 42 percent, but substantial difference in the two instruments.
• Optec NGN-3—Unavailable.
• Andersen aethalometer—Insufficient data.

During laboratory tests when the concentrations ranged to 350 µg/m³ and the humidity was above 70 percent, the approximate performance was:

• MET One GT-640
  Heater: Underestimated by 6 percent.
  No Heater: Underestimated by 15 percent with some data scatter.
• MIE DataRam
  Heater: Overestimated by 40 percent.
  No Heater: Overestimated by 30 percent.
• Radiance Research
  Heater: Overestimated by 51 percent.
  No Heater: Overestimated by 65 percent.
• Optec NGN-3
  Heater: Underestimated by 5 percent.
  No Heater: Unavailable.
• Andersen aethalometer
  Heater: Unavailable.
  No Heater: Unavailable.

These optical instruments are not suited for evaluating whether particles in the air are from biomass smoke or some other source; nor are they intended to ascertain whether ambient air-quality standards are being met. The best use for these instruments is to determine whether the local aerosol concentration is relatively high or low and whether concentrations are going up or down. For these purposes, each of the instruments has some capability.

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This page last modified October 21, 2002
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