Beta Attenuation Monitor (BAM) and the more portable E-BAM. The BAM and E-BAM collect particulate samples on a filter tape and estimate concentration through a process called beta ray attenuation. For this process beta particles from a naturally occurring radioactive isotope are emitted through clean filter tape and counted. Next, sampled air is passed through the exposed filter tape and particles are deposited. Finally, beta particles are passed through the tape again and recounted. The second count will be lower than the first, because beta particles will have been absorbed by the deposited particulate. The instrument then uses conversion formula to estimate the total mass of the deposited particulate. The estimated mass is divided by the volume of sampled air to calculate the average concentration in mass per unit volume. The exposed filter tape will advance automatically and begin a new collection after a user-specified time period or when the filter becomes clogged.
Source: National Wildfire Coordinating Group. In Draft. Smoke Management Guide for Prescribed and Wildland Fire. Second Edition.