Which particle category disperses most efficiently in confined spaces?

• A. Large droplets (>100 micrometers)
• B. Dust particles (10-100 micrometers)
• C. Droplet nuclei (2-10 micrometers)
• D. Aerosols (>1000 micrometers)

Answer: (C)

In confined spaces, how long a particle stays in the air and how easily it follows air currents determine how widely it disperses. The smallest respiratory particles, about 2–10 micrometers, stay suspended for long periods and are readily carried by ventilation and room airflows, so they spread throughout the space. They can also be generated repeatedly as droplets evaporate, leaving these tiny “nuclei” that remain airborne. Larger droplets, over 100 micrometers, settle quickly under gravity and deposit on surfaces, so they don’t travel far. Dust particles in the 10–100 micrometer range settle faster than the droplet nuclei but can be moved briefly by air currents; they don’t disperse as efficiently over time. Very large aerosols, greater than a millimeter, are effectively too heavy to remain suspended at all.