What is the current air quality in San Francisco today?

San Francisco's air quality varies throughout the day based on weather, traffic, and seasonal factors like wildfire activity. Check our live AQI map above for real-time air quality conditions in San Francisco and surrounding Bay Area neighborhoods. The AQI scale ranges from 0-500, with 0-50 (green) being good air quality and higher numbers indicating increased health concerns.

What does AQI mean and how is it measured?

AQI stands for Air Quality Index, a standardized measurement system used by the EPA to communicate daily air pollution levels. The AQI measures five major pollutants: ground-level ozone, particulate matter (PM2.5 and PM10), carbon monoxide, sulfur dioxide, and nitrogen dioxide. Each pollutant has its own AQI value, and the highest reading becomes the overall AQI for that area. AQI values range from 0 to 500, with higher numbers indicating greater health risks.

What are the AQI color categories and their meanings?

The AQI uses a color-coded system: Green (0-50) means good air quality with minimal risk. Yellow (51-100) is moderate with slight concern for sensitive individuals. Orange (101-150) is unhealthy for sensitive groups like those with asthma or heart disease. Red (151-200) is unhealthy for everyone. Purple (201-300) is very unhealthy and requires limiting outdoor exposure. Maroon (301-500) is hazardous and dangerous for all groups.

Why is San Francisco's air quality sometimes poor?

San Francisco's air quality can be affected by several factors: wildfire smoke (especially during California's fire season from May through October), vehicle emissions from heavy traffic on major highways, marine fog that can trap pollutants near ground level, industrial activities in the greater Bay Area, and temperature inversions that prevent pollutants from dispersing. During wildfire events, smoke can travel hundreds of miles, significantly impacting air quality throughout the region.

How can I protect my indoor air quality when outdoor AQI is high in San Francisco?

When San Francisco's outdoor AQI reaches unhealthy levels, protect your indoor air by: (1) Keep windows and doors closed to prevent outdoor pollution from entering. (2) Run your HVAC system with a high-efficiency MERV 13 air filter, which captures 98% of particles including PM2.5 from wildfire smoke. (3) Avoid activities that generate indoor pollution like cooking with gas or burning candles. (4) Consider using a portable air purifier in your main living areas. (5) Replace your air filters more frequently during poor air quality events—every 30-60 days instead of 90 days.

What air filter MERV rating is best for wildfire smoke in San Francisco?

For protection against wildfire smoke, which produces fine PM2.5 particles, a MERV 13 air filter is recommended by the EPA and air quality experts. MERV 13 filters capture at least 85% of particles in the 1.0-3.0 micron range and are effective against smoke, smog, and other fine particulates. For homes in the San Francisco Bay Area that regularly experience wildfire smoke events, upgrading from a standard MERV 8 to MERV 13 provides significantly better protection without requiring HVAC system modifications in most cases.

When is wildfire season in San Francisco and the Bay Area?

California's wildfire season typically runs from May through October, with peak activity occurring between August and October. However, climate change has extended this season in recent years, with significant fires occurring as early as April and as late as December. San Francisco residents should monitor AQI levels closely during these months and have MERV 13 air filters on hand to protect indoor air quality when smoke events occur.

How often should I change my air filter when San Francisco has poor air quality?

During normal air quality conditions, replace your air filter every 60-90 days. However, when San Francisco experiences poor air quality events like wildfire smoke or high smog days, check your filter weekly and plan to replace it every 30-45 days. Your filter will accumulate particulates faster during these events. Signs that your filter needs changing sooner include visible darkening, reduced airflow from vents, and increased dust accumulation in your home. Setting up an auto-delivery subscription ensures you always have fresh filters on hand when you need them.

Live Air Quality Index AQI Map San Francisco California Today

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