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

Evaluation Results and Discussion (continued)

Real-Time Continuous Monitoring Results (continued)

Met One GT-640 (continued)

2000 Laboratory Tests (continued)—Results from the high-humidity tests (figures 16 and 17) show both instruments underestimated the mass concentrations. Instrument No. 1 without its inlet heater underestimated mass concentrations by 15 percent (slope = 0.85, R² = 0.63). Instrument No. 2 with its inlet heater installed underestimated mass by 6 percent (slope = 0.94, R² = 0.61). Comparison of the results of the two Met One instruments shows that the instrument with the inlet heater (Met One No. 2) read higher than the instrument without the heater (Met One No. 1) by 11 percent (slope = 1.11, R² = 0.98).

Figure 16—Results of the high-humidity laboratory tests.
Instrument No. 1 did not have the inlet heater installed.

Figure 17—Comparison of the laboratory high-humidity results
from two Met One GT-640 instruments.

Discussion—The concentrations measured by the Met One GT-640 did not correlate well with those measured by the Federal Reference Method sampler. This could be due to the small number of data points collected. The 2000 Laboratory tests show the instrument grossly underestimated the mass concentrations by 40 to 50 percent. Although all the real-time continuous instruments underestimated mass concentrations to some degree during the 2000 laboratory tests, the Met One showed the largest discrepancy. Correlation between the two Met One instruments was poor.

One instrument read 26 percent higher than the other. Met One has upgraded the GT-640 to improve the instrument's performance at low particulate concentrations. This may improve the consistency among identical instruments.

The high-humidity tests yielded positive results. In theory, the inlet heater should be drying the particulates as they enter the optical chamber, lowering the mass concentration estimate from the instrument. In this study, even though the instrument with the inlet heater was still reading higher than the one without the inlet heater, the difference between the two decreased (from 26 percent to 11 percent), indicating the heater was removing some moisture from the particulates.

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