San Diego, California vs Los Angeles, California Air Quality
Side-by-side air quality comparison using 10 years of EPA monitoring data. Both cities have identical Air Quality Grades.
| Metric | San Diego, California | Los Angeles, California |
|---|---|---|
| Air Quality Grade | D (36/100) | D (36/100) |
| Current Median AQI | 67 (Moderate) | 67 (Moderate) |
| 5-Year Average AQI | 67 | 75 |
| 10-Year Trend | → Stable (+2) | ↓ Improving (-15) |
| Unhealthy Days/Year | 32 | 100 |
| Primary Pollutant | Fine Particulate Matter (PM2.5) | Fine Particulate Matter (PM2.5) |
Side-by-Side Analysis
San Diego, California and Los Angeles, California have comparable overall air-quality profiles with identical grades and similar median AQI. The meaningful differences for residents are in trend direction (where each city is headed) and dominant pollutant (which seasonal and health patterns dominate locally).
The two cities are moving in opposite directions: San Diego, California is stable (+0.1 AQI/yr) while Los Angeles, California is improving (-0.9 AQI/yr). Over time, today's ranking may flip if these trends hold.
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, San Diego, California averages roughly 32 unhealthy air days per year (AQI above 100, where sensitive groups should limit outdoor exertion) versus 100 for Los Angeles, California. That 68-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.
Frequently Asked Questions
San Diego, California and Los Angeles, California have identical Air Quality Grades. Both score 36/100 based on 10 years of EPA data.
San Diego, California averages 32 unhealthy air days per year (5-year average), while Los Angeles, California averages 100. Unhealthy days are those when AQI exceeds 100 and sensitive groups should limit outdoor activity.
San Diego, California's primary pollutant is Fine Particulate Matter (PM2.5), while Los Angeles, California's is Fine Particulate Matter (PM2.5). Both cities share the same dominant pollutant.
Source: EPA Outdoor Air Quality Data, 2026.
The side-by-side above pulls the EPA Air Quality System data data for both entity A and entity B. What follows is the interpretation — which specific axes carry the most weight for entity A versus entity B, and which differences are large enough to influence a real decision.
For households or analysts using this comparison as a decision input, the right framing is usually not "which is better" in aggregate but "which is better for the specific decision in front of you." EPA Air Quality System data captures the raw data; the framing depends on whether the question is investment, residency, planning, or research.