Air Quality

Air quality emergencies can be caused by particle pollution (particulate matter) such as dust, dirt, soot, smoke, or liquid droplets. Some particles are large enough to see — for example, wildfire smoke. Others are so small they’re invisible.

In the Bay Area, meteorological conditions such as inversion layers can trap these particles close to the ground. While ocean breezes and San Francisco fog often clear pollution, there are periods — sometimes lasting several days — when poor air quality lingers.

The Bay Area Air Quality Management District may issue “Spare the Air” alerts in anticipation of unhealthy air days.

More information is available at:

• Stanford EHS Air Quality Decision Making Matrix
• CDC – Air Quality and Physical Activity

Wildfire Smoke Drift

Major wildfires in California — even distant ones in the Sierra Nevada or northern states — can produce significant smoke drift that impacts campus air quality.

When an air quality emergency occurs, AlertSU will notify the community and advise protective actions:

• Stay indoors as much as possible with windows and doors closed.
• In a car, use air recirculation mode on the car’s AC system.
• Drink water to stay hydrated and help reduce throat and airway irritation.
• Limit prolonged or strenuous outdoor activity.
  • Prolonged exertion: several hours of light outdoor work or recreation.
  • Heavy exertion: vigorous activity such as long runs or high-intensity outdoor labor.
• Shift outdoor activities to times when conditions have improved.
• When on the main campus, use the Marguerite Shuttle instead of walking long distances outdoors.
• Check AirNow.gov for current conditions.

Safe Use of N95 Masks

Stanford follows Cal/OSHA guidance on N95 respirator use during air quality emergencies.

• For most healthy individuals, the best protection is to stay indoors and limit strenuous outdoor activities.
• Sensitive groups (people with lung or heart disease, asthma, or chronic illness) should consult their healthcare provider before using a mask.
• Masks should be fit-tested and worn clean-shaven for an effective seal.
• Avoid spending unnecessary time outside even when wearing an N95. 

Additional guidance can be found in the Cal/OSHA N95 FAQs.

Indoor Air Quality on Campus

Stanford buildings use high-efficiency MERV-13 air filters, capturing at least 90% of fine particulate matter (as small as 1 micron).

During wildfire smoke events:

• Doors and windows should remain closed.
• Ventilation systems may reduce outdoor air intake to limit smoke entry.
• Some odors may still be detectable indoors, but air quality remains better than outdoors.

Laboratory buildings continue to supply 100% outdoor air with filtration due to safety requirements, even on days when smoke odor may be noticeable. There is no risk to health and safety by continuing to operate HVAC in this manner.

Toxic Chemical Release

In rare cases, industrial spills or fires can release toxic chemicals into the air. If odors or symptoms are expected on campus with air quality above a certain air quality index (AQI) level per the decision matrix, AlertSU may direct the community to shelter in place and cancel outdoor activities.