What effect does significant air movement over an open-faced charcoal canister have on radon measurement?

The correct understanding here is that significant air movement over an open-faced charcoal canister can actually result in an increased measurement of radon by allowing more radon to be absorbed onto the charcoal. When air is moving vigorously, it helps to sample a larger volume of air in a given time frame, which increases the likelihood of radon molecules encountering the charcoal. This interaction occurs because the charcoal is designed to adsorb radon from the air, and enhanced air movement can increase the effective concentration of radon that the canister captures.

In practical terms, if air movement is significant, the canister can collect radon from a broader area and, consequently, the resulting measurement can be higher, reflecting a greater concentration of radon. This process highlights the importance of maintaining controlled conditions during radon measurement so that variables like air movement are kept in check to ensure accurate and reliable readings.