Final answer:
Airborne pathogens are typically associated with particles less than 5 micrometres in diameter, which can include viruses that cause respiratory diseases like the flu and common cold, and these can remain suspended in the air for long periods.
Step-by-step explanation:
To be considered airborne, a pathogen typically is found in particles called aerosols, which are less than 5 micrometres (μm) in diameter. Particles of less than 10 micrometres (PM10s) and those less than 2.5 micrometre (PM2.5s) can penetrate deeply into the lungs. These tiny particles can carry viruses, such as those causing the flu and the common cold, and can be inhaled by people, potentially causing respiratory diseases. Due to their small size, these pathogens can remain suspended in the air for a significant amount of time and be transmitted over distances, which is a key characteristic of airborne pathogens.