​​​Indoor air quality can play a key role in the transmission of airborne viruses; the tips below can be used to improve your indoor air quality. Improving indoor air quality also creates a healthier environment by limiting exposure to harmful chemicals and wildfire smoke (PDF).

  ​​​

​In general, being outdoors when air quality is not harmful, is safer than b​eing

​​​indoors where the risk of tran​​smission of respiratory viruses is higher. In poorly-ventilated indoor environments, exhaled virus particles can remain airborne and build up in the air making them more likely to be inhaled and cause infection. ​​Good ventilation helps reduce virus      accumulati​on and transmission. ​​​Californians​​ can improve indoor air quality by opening doors and windows, using fans to bring in fresh air, optimizing mechanical ventilation (or HVAC) systems, and using portable air cleaning devices. 

​​​Open Doors and Windows, Use Fans to Bring Fresh Air Inside​​​​​

Keep windows and doors open as much as possible when weather and safety considerations allow. Use portable fans to increase the effectiveness of open windows. Place fans near or in open windows pointing outward, to remove room air to the outdoors. The exhausting of air can also help draw in fresh air from other open windows and doors by promoting gentle cross-ventilation. When fans are used, position them so air does not blow in the direction of one person to another (as this could promote virus spread). Ceiling fans may result in improved air mixing, provided outdoor air is being introduced into the space. ​​​​

Optimize Your Mechanical Ventilation (or HVAC) System  ​​

If your space has a mechanical heating, ventilation, and air conditioning (or HVAC) system, keep it running continuously while the space is occupied, to the extent feasible. This is done by setting the fan on the system’s thermostat to the “ON” position instead of “AUTO.” This will cause the system’s fan to bring in outside air continuously. Your HVAC system serves two purposes: it brings fresh outside air in, and also circulates air through filters to remove particles. Be sure to install high quality air filters in your system; MERV 13 or greater are best if your system has the capacity. Be sure to perform all routine maintenance on your ventilation system and replace air filters when recommended. For employers, contact and involve maintenance staff and/or ventilation professionals to assist with these updates. ​​​

Purchase Portable Air Cleaning Devices as Needed  ​​​

Use portable air cleaning devices (PACs) as needed as a supplemental measure when opening windows and doors and improving your mechanical ventilation system aren’t possible. Use devices that circulate air through high quality HEPA filters. HEPA filters remove infectious particles by filtering them out of the air. Avoid devices that advertise ionizer, ozone, or other cleaning methods that add chemicals to the air.  Choose a device that is appropriately-sized for your space (1). You may need multiple devices if your space is large. Place your PAC toward the center of your space where it does not pose a tripping hazard. Avoid placing devices in unused corners of rooms or beneath tables, as they will not effectively clean the air when in these locations.  ​​​​