What is required to accurately calculate the Equilibrium Ratio (ER)?

The Equilibrium Ratio (ER) is a crucial component in understanding radon exposure and its potential health risks. To accurately calculate the ER, simultaneous measurements of radon gas and its decay products are necessary. This is because the ratio is defined by the concentration of radon in the air compared to the concentration of radon decay products, such as polonium-210. By measuring both radon and its decay products at the same time, one can determine the extent to which radon is in equilibrium with its decay products, which is important for assessing exposure risk.

Having results from past weather measurements, a single measurement of radon levels, or long-term exposure data by themselves may not provide the necessary information to establish the dynamic relationship between radon and its decay products. Only simultaneous measurements allow for an accurate representation of this relationship, making option B the correct choice in calculating the Equilibrium Ratio.