Los Angeles, California vs San Francisco, California Air Quality

Side-by-Side Analysis

San Francisco, California outperforms Los Angeles, California on overall air quality with a Grade B (70/100) versus D (36/100). San Francisco, California's 5-year median AQI of 38 sits in the "Good" range, while Los Angeles, California averages 75 ("Moderate") — a 38-point gap that shows up consistently in year-over-year readings, not just in a single year.

Both cities are on improving trajectories — Los Angeles, California at roughly 0.9 AQI/yr cleaner and San Francisco, California at 0.6 AQI/yr cleaner. That mirrors the broader U.S. pattern of falling pollution as cleaner vehicles, cleaner power generation, and tighter emissions standards take effect.

What's in the Air

Both cities share the same dominant pollutant: Fine Particulate Matter (PM2.5). These cities' dominant issue is fine particulate matter — typically driven by combustion (vehicles, wildfire smoke, industry, residential wood burning). PM2.5 is the air pollutant most strongly linked to long-term cardiovascular and respiratory disease because the particles penetrate the bloodstream.

Health Implications

Over a 5-year window, Los Angeles, California averages roughly 100 unhealthy air days per year (AQI above 100, where sensitive groups should limit outdoor exertion) versus 2 for San Francisco, California. That 98-day gap matters most for residents with asthma, COPD, heart disease, or pregnancy — and for outdoor workers, who accumulate the most cumulative exposure. The city with fewer unhealthy days offers a meaningfully different baseline risk picture for sensitive populations. For long-term residents, the cleaner-air city is associated with measurably better outcomes on respiratory disease, cardiovascular events, and life expectancy — Harvard cohort research consistently finds 0.5 to 1.0 years of additional life expectancy for each 10-µg/m³ reduction in long-term PM2.5 exposure.