What is a TEOM and how does it differ from a BAM for PM monitoring?

• A. A TEOM measures mass by beta attenuation; a BAM tracks resonant frequency.
• B. TEOM measures mass by tracking the resonant frequency of a tapered element with a filter; BAM uses beta attenuation to estimate PM mass; TEOM can underrepresent semi-volatile PM due to heating.
• C. TEOM and BAM are identical methods.
• D. BAM uses a filter that is weighed in a lab.

Answer: (B)

The essential idea is how each instrument translates particles on a filter into a mass measurement. A TEOM (Tapered Element Oscillating Microbalance) uses a filter attached to a thin, tapered element that vibrates. As particles collect on the filter, the added mass slows the oscillation; the change in resonant frequency is translated into a mass concentration. A BAM (Beta Attenuation Monitor) passively measures PM by sending beta radiation through the PM collected on a moving filter and observing how much the signal is attenuated. That attenuation correlates with the mass on the filter, giving a continuous mass readout.

A key difference is that TEOM systems typically heat the sample to improve measurement stability and humidity control. That heating can cause semi-volatile particles—organic components and some inorganic salts—to volatilize and be lost from the filter, leading to an underestimation of the true PM mass. BAM does not rely on heating the sample in the same way, so it generally preserves semi-volatile mass better, though it has its own limitations.

So, TEOM determines mass from a change in oscillation frequency of a heated tapered element with a filter, and BAM determines mass from beta attenuation through PM on a filter tape, with TEOM’s heating potentially causing underrepresented semi-volatile PM.