What does the active sampling method utilize to collect air samples?

The active sampling method utilizes a vacuum pump to collect air samples. This method relies on a mechanical device that actively draws air through a collection medium, such as a filter or sorbent tube, at a controlled flow rate. By using a vacuum pump, active sampling allows for the precise measurement of specific constituents in the air over a designated period, ensuring a more accurate representation of air quality or contaminant levels in the environment being monitored. This control over the airflow enables more effective sampling of airborne pollutants compared to passive methods, which do not use additional energy to collect samples.

In contrast, other methods listed rely on different physical principles, such as gravity or natural airflow, which do not provide the same level of control or specificity in sampling. Additionally, passive diffusion involves capturing contaminants as air naturally diffuses without the aid of a pump, which may not be as effective for certain applications where precise measurement is critical.