Which PM monitoring method uses beta attenuation to estimate mass and is less affected by sample heating?

• A. Nephelometer
• B. TEOM
• C. BAM
• D. Gravimetric lab weighing

Answer: (C)

The main idea here is that some PM monitors estimate mass by how much beta radiation is absorbed by particles collected on a filter. In this method, air passes through, PM settles on a filter, and a fixed beta source shines through it. The detector catches the transmitted beta particles; as more mass builds up on the filter, more beta is absorbed and the detected signal drops. The instrument then converts that attenuation into a mass concentration in the air. This approach gives a direct mass estimate without needing to dry or heat the sample.

It’s less affected by sample heating because the measurement doesn’t rely on removing moisture or volatile components to determine mass. Methods that heat the sample to evaporate water or organics can change the true mass (leading to under- or overestimation). Since beta attenuation measures the mass deposited on the filter as-is, ambient temperature and humidity don’t skew the result as much. In short, beta-attenuation monitoring provides continuous mass estimation through radiation attenuation, avoiding the heating-related biases seen in some other techniques.