Which statement correctly describes droplet nuclei?

• A. Dust particles are larger than droplets and settle more quickly.
• B. Droplet nuclei are 10-100 micrometers in diameter and settle rapidly.
• C. Droplet nuclei cannot be removed by air filtration.
• D. Droplet nuclei are 2-10 micrometers in diameter, settle slowly, and can be removed by electrostatic precipitation.

Answer: (D)

Droplet nuclei are the tiny residues left after respiratory droplets evaporate. Because they’re small enough to remain suspended in air, they can be carried by air currents and travel beyond close contact distances, contributing to airborne transmission. Their typical size is around 2–10 micrometers, which gives them a slow settling rate so they stay airborne longer and can be inhaled deeply into the lungs. Importantly, they can be removed by air-cleaning methods such as filtration and electrostatic precipitation, since these particles fall within the size range that such systems are designed to capture. Larger dust particles settle quickly and aren’t representative of droplet nuclei, and air filtration can indeed remove particles in this size range, so statements claiming they cannot be removed by filtration aren’t accurate.