What instrument is typically used to measure flow rates during air sampling?

The instrument typically used to measure flow rates during air sampling is the rotameter. This device operates based on the principle of variable area flow measurement. As air flows through the rotameter, it lifts a float within a tapered tube, and the height of the float indicates the flow rate on a calibrated scale. This makes it particularly useful in air sampling applications, as maintaining a specific flow rate is crucial for accurate analysis of airborne contaminants, including asbestos fibers.

The other instruments listed serve different purposes. A barometer measures atmospheric pressure, which is not directly related to flow rates in air sampling. A hydrometer measures the specific gravity or density of liquids, and a thermometer is used to measure temperature. None of these instruments provide the functionality needed to accurately gauge air flow rates in sampling procedures.