Wells curve

Graphical representation of droplet behavior in air

Wells curve

The Wells curve is a graphical representation that describes the behavior of respiratory droplets in the air, particularly focusing on their evaporation and falling dynamics. This concept is crucial in understanding the transmission of respiratory diseases and is named after William F. Wells, a pioneer in the study of airborne infections.

The Wells falling and evaporation curve of droplets

Overview

The Wells curve illustrates how droplets of different sizes behave once expelled into the air. When a person coughs, sneezes, or talks, droplets of varying sizes are released. These droplets can either evaporate, fall to the ground, or remain suspended in the air, depending on their size and the environmental conditions such as humidity and temperature.

Droplet Size and Behavior

Sizes of respiratory droplets

Droplets are typically categorized by their size:

• Large droplets (greater than 100 micrometers): These droplets tend to fall to the ground quickly due to gravity, usually within a meter or two from the source.
• Medium droplets (10 to 100 micrometers): These droplets may partially evaporate before reaching the ground, depending on the ambient humidity.
• Small droplets (less than 10 micrometers): These droplets can evaporate completely, leaving behind droplet nuclei that can remain airborne for extended periods and potentially travel longer distances.

Environmental Factors

The behavior of droplets is significantly influenced by environmental factors:

• Humidity: High humidity slows down the evaporation process, allowing droplets to remain larger and fall more quickly. Conversely, low humidity accelerates evaporation, increasing the likelihood of droplet nuclei formation.
• Temperature: Higher temperatures can increase the rate of evaporation, affecting the size and longevity of droplets in the air.

Droplet falling-evaporation curves for different humidities

Implications for Disease Transmission

Understanding the Wells curve is essential for controlling the spread of airborne diseases. It helps in designing effective infection control measures, such as maintaining adequate ventilation, using face masks, and implementing social distancing to reduce the risk of transmission.

Related pages

• Airborne transmission
• Droplet transmission
• Infection control
• William F. Wells