Throughout the COVID-19 pandemic, three things have been constantly recommended as a way to combat the spread of the new coronavirus, also known as SARS-CoV-2: mask wear, hand washing, and physical distancing. With recent studies confirming the earlier suspicion that SARS-CoV-2 is spread primarily via aerosol or droplets, ventilation comes into play and becomes key as winter approaches. The risks however are highly dependent on the environment.
While all measures should be practiced at all times, this table, compiled based on data from L Zhao, Y Qi, and others, will give you a guide to prioritize certain measures over others depending on the environment:
| Temperature | Humidity | Highest risks | Key mitigation strategy | Mitigation actions |
| < 50° F | > 60% | Droplet spreading distance (very far) | Physical distancing | Distance >6ft (up to 20ft recommended) |
| < 50° F | 50% | Time of survival on surface | Hand washing | Proper hand washing techniques (20 seconds, soap and water) |
| < 50° F | < 40% | Aerosolization rate (low) | Ventilation | Open windows, install indoor air filters, … |
| 72° F | > 60% | Droplet spreading distance (far) | Physical distancing | Distance >6ft at all times |
| 72° F | 50% | # of infectious particles in the air (medium) | Ventilation | Open windows, install indoor air filters, … |
| 72° F | < 40% | Aerosolization rate (high) # of infectious particles in the air (medium) |
Ventilation + Mask wear |
Open windows, install indoor air filters, … Wear high quality and fitting masks at all times |
| > 86° F | > 60% | # of infectious particles in the air (medium-high) | Ventilation + Mask wear |
Be outdoors, open windows, install indoor air filters, … Wear high quality and fitting masks at all times |
| > 86° F | 50% | # of infectious particles in the air (high) | Ventilation + Mask wear |
Be outdoors, open windows, install indoor air filters, … Wear high quality and fitting masks at all times |
| > 86° F | < 40% | Aerosolization rate (very high) Aerosol particle size (very large) # of infectious particles in the air (very high) |
Physical distancing + Ventilation + Mask wear |
Because of the lowest droplet travel distance! Be outdoors, open windows, install indoor air filters, … Wear high quality and fitting masks at all times |
In the end, the practice of all 4 measures (mask wear, hand washing, physical distancing, and ventilation) is key to slow down the second surge of the virus that is sure to come when activities are moved more indoors with the colder weather this winter.
Based on this report for the local area, humidity will be highest in the morning at around 80%, while it is lowest in the afternoon at around 60%.
High humidity conditions allow for more (larger) droplets to linger in the air longer, and to travel further distance. So organize more of your outdoor activities in the morning, and wear a quality and fitting mask. Most masks, even fabric ones, are very good at stopping most large droplets.
Lower humidity conditions instead increase the aerosolization rate (the probability of larger droplets turning into aerosol particles) so ventilation is key to dilute and freshen the air. Proper wear of a quality and fitting mask is criticial. A quality surgical mask or better is recommended.
Let’s all keep each other safe this winter and slow the spread.
Feature Image Credit: United Nations COVID-19 Response on Unsplash
Available further reading:
This excellent article in the Wall Street Journal (subscription required) detailed very well the benefits of ventilation for indoor enviroments.
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