Bias Sources and Corrections in TEOM Technology

Researchers at the National Institute for Occupational Safety and Health have used tapered element oscillating microbalances (TEOM) in laboratory settings. The TEOMs have assessed the mass concentration of laboratory-generated particulates in experimental dust chambers and provided a reference method for comparison with other particulate-measuring instruments. Current NIOSH research is focused on further adapting TEOM technology as a wearable personal dust monitor (PDM) for coal mine workers. The history of TEOM technology describes the oscillating tapered tube mathematically as a simple harmonic oscillator. However, analysis of the new PDM test data showed a bias dependency on the starting frequency f o. This result prompted a rigorous investigation to uncover the source of the bias and if the bias source is applicable to the 1400 TEOM. Based on the above results, a significantly improved theoretical description of TEOM performance has been developed. Average bias for each group of PDMs is calculated and compared to the results of the accuracy tests performed. Accompanying these biases are estimates of the average bias spans of the new PDMs in comparison to the pre-commercial PDMs. The theory was also applied to the Model 1400 TEOM data to evaluate whether there is agreement. The new theory of TEOM operation provides a good account for both the bias and bias span. Given that TEOM technology has been used for decades around the world to monitor atmospheric particulate contaminants as well as many other aerosols, quantification and correction of this source of bias should result in more accurate assessments.