Explain the difference between active sampling and passive sampling for air contaminants.

• A. Active sampling uses a pump to draw air through a sorbent or filter; passive relies on diffusion to collect contaminants without a pump over time.
• B. Passive sampling relies on diffusion to collect contaminants; active uses a pump.
• C. Active sampling and passive sampling are the same.
• D. Passive sampling uses a pump to collect samples.

Answer: (A)

Active sampling and passive sampling differ in how air is collected and analyzed. In active sampling, a pump is used to pull a known volume of air through a collection medium, such as a sorbent tube or a filter, so you can relate the mass collected to an exact concentration. This setup gives controlled, time-specific data and is useful when you need precise measurements over a defined period or when contaminant levels are low and you want to maximize sample volume.

In passive sampling, there is no pump. Contaminants reach and accumulate in the collection medium by diffusion over time, and the result is typically an integrated measure of exposure over the deployment period. This approach is simpler, requires no power, and is good for long-term or remote monitoring, but it relies on diffusion dynamics and environmental conditions to interpret the concentration.

So the best choice states that active sampling uses a pump to draw air through a sorbent or filter, while passive sampling relies on diffusion to collect contaminants without a pump. The other descriptions either omit the pump, claim the methods are the same, or assign a pump to passive sampling.