现买现卖：droplets（飞沫） + aerosols（气溶胶） + 物体表面。飞沫传播一般不超过6尺气溶胶远些。

Larger, heavier respiratory droplets can travel up to 6 feet, but then they fall to the ground. Smaller, aerosolized particles, however, can get caught in air flows and move throughout a space, infecting people at further distances.

"It's really the size of the droplet nuclei that defines an aerosol-borne infection versus a droplet-borne infection," said Monica Gandhi, MD, MPH, an infectious disease expert at the University of California San Francisco. She added that in recognizing the airborne nature of COVID-19, we acknowledge that "it's most effectively transmitted in closed, indoor spaces, and that ventilation is one of the most important things to mitigate the virus."

When an infected individual emits aerosols, they are more likely to spread disease in poorly ventilated, indoor spaces. Outdoors, however, the virus can disperse more easily. Several epidemiological studies have demonstrated the potential for COVID-19 aerosols to infect others indoors.