Taking Steps for Cleaner Air

Published on 7/16/24. Last updated on 2/25/25.

Taking steps for cleaner air is a core prevention strategy to lower the chances of catching or spreading a respiratory virus (such as COVID-19, Flu, RSV). This can mean bringing in fresh outside air, purifying indoor air, or gathering outdoors. Virus particles do not build up in the air outdoors as much as they do indoors.

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How It Works

Taking steps for cleaner air, along with other prevention actions, can help protect people from respiratory viruses.

  • Respiratory viruses, like COVID-19, spread in the air between people. This can happen when you:
    • Breathe,
    • Speak,
    • Sing,
    • Exercise,
    • Cough, and
    • Sneeze.
  • These viruses spread more easily in indoor, crowded spaces with poor airflow. To lower you chances of getting sick it helps to improve air quality by increasing airflow, cleaning the air, or gathering outdoors.
An image that shows the difference between bad ventilation and good ventilation inside a home.

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Steps You Can Take

An image of a box fan blowing air.
  • Bring as much fresh air into your home as possible by opening doors and windows and/or using exhaust fans.
An image of a thermostat.
  • If your home has a central heating, ventilation, and air conditioning system (HVAC, a system with air ducts that go throughout the home) that has a filter:
    • Set the fan to the "on" position instead of "auto" when you have visitors, and
    • Use pleated filters. Change your filter every three months or according to the manufacturer's instructions.
An image of a portable high-efficiency particulate air cleaner.
  • Use a portable high-efficiency particulate air (HEPA) cleaner.
An image of a women walking outside.
  • Move activities outdoors, where airflow is best.

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Steps Organizations Can Take

Circulating (ventilation) and cleaning (filtration) the air can improve the indoor air quality in buildings, like offices, schools, and larger buildings. It is important to have good ventilation and filtration systems in place to prevent the spread of respiratory viruses.

An image of air blowing through an open window.

Ventilation moves air into, out of, or within a room. There are two types of ventilation:

  • Natural ventilation is when air flows on its own from outdoor to indoor spaces. This can be through open windows or doors.
  • Mechanical ventilation moves outdoor air into a building. Most offices, schools, and other larger buildings have mechanical ventilation.
An image of a filter trapping airborne particles.

Filtration traps particles on a filter to remove them from the air. Portable HEPA cleaners can be used to filter the air.

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Resources

County of San Diego

California Department of Public Health (CDPH)

Centers for Disease Control and Prevention (CDC)

United States Environmental Protection Agency (EPA)

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Call the Epidemiology Unit at (619) 692-8499, or send an e-mail, for more information.