Air Quality in San Ysidro, CA: Moderate (59 AQI)
AQI 59 · Moderate · Ozone · Updated 2026-05-03
San Ysidro's air quality is moderate. Unusually sensitive people should consider reducing prolonged outdoor exertion.
Data: EPA AirNow, FEMA National Risk Index Last verified: 2026-05-03
What is AQI?
The Air Quality Index (AQI) is a standardized scale from 0 to 500 that measures air pollution levels. 0-50 is "Good," 51-100 is "Moderate," 101-150 is "Unhealthy for Sensitive Groups," and above 150 is "Unhealthy" for everyone. AQI tracks five major pollutants: ground-level ozone, particulate matter (PM2.5 and PM10), carbon monoxide, sulfur dioxide, and nitrogen dioxide. San Ysidro's average AQI of 59 falls in the "Moderate" range.
How do wildfires affect air quality?
Wildfire smoke contains fine particulate matter (PM2.5) that can travel hundreds of miles and dramatically spike AQI readings. During fire season, even cities far from active fires can experience unhealthy air. HEPA air purifiers (rated for PM2.5) are the most effective indoor protection. Check AirNow.gov for real-time conditions during fire season.
Air Quality by ZIP Code in San Ysidro
AQI varies across San Ysidro's 2 ZIP codes based on proximity to pollution sources and local geography.
| ZIP Code | AQI | Category | Wildfire | Mold | |
|---|---|---|---|---|---|
| 92173 | 64 | Moderate | 84 | 26 | View report → |
| 92143 | 54 | Moderate | 87 | 12 | View report → |
Air Quality Overview
San Ysidro, California has moderate air quality with an average AQI of 59. Air quality is acceptable, though some pollutants may be a concern for a small number of people who are unusually sensitive to air pollution. The dominant pollutant is Ozone.
The Air Quality Index (AQI) is an EPA-standardized scale from 0 to 500. Values below 50 are "Good," 51-100 "Moderate," 101-150 "Unhealthy for Sensitive Groups," 151-200 "Unhealthy," 201-300 "Very Unhealthy," and above 300 "Hazardous."
Dominant Pollutant: Ozone
Ground-level ozone forms when pollutants from cars, power plants, and industrial facilities react with sunlight. Unlike stratospheric ozone, ground-level ozone is harmful to breathe.
Health effects of ozone exposure:
- Irritation of the respiratory system
- Reduced lung function
- Aggravation of asthma and chronic lung diseases
- Increased susceptibility to respiratory infections
Peak times: Ozone levels are typically highest on hot, sunny afternoons. Exercise outdoors in the morning when levels are lower.
Air Quality by ZIP Code in San Ysidro
AQI varies across San Ysidro's 2 ZIP codes based on proximity to pollution sources, traffic patterns, and local geography:
Wildfire Smoke Risk
San Ysidro has an elevated wildfire smoke risk with an average smoke risk score of 86 (scale 0-100). There have been 69 fires recorded within 100 km of city ZIP codes.
| Metric | Value |
|---|---|
| Avg. smoke risk score | 86 |
| Max smoke risk score | 87 |
| Fires within 100 km | 69 |
| High-risk ZIP codes | 2 |
Wildfire smoke contains PM2.5, carbon monoxide, and volatile organic compounds. Even short-term exposure can trigger asthma attacks and respiratory distress.
Indoor Mold Risk
San Ysidro has an average mold risk score of 19 out of 100.
| Factor | Value |
|---|---|
| Mold risk score | 19/100 |
| Average humidity | 57% RH |
| High-risk ZIPs | 0 |
| Peak season | winter high |
Mold risk is influenced by humidity levels, housing age (older homes have more moisture issues), flood history, and water infrastructure quality. Indoor humidity above 60% creates favorable conditions for mold growth.
Signs of mold problems: musty odors, visible growth on walls or ceilings, worsening allergies indoors, condensation on windows. Professional mold testing ($300-$600) can identify hidden issues.
Health Recommendations
With moderate air quality (AQI 59), most people can be active outdoors. Sensitive groups should take precautions:
- Sensitive groups (asthma, COPD, heart disease): consider reducing prolonged outdoor exertion
- Keep windows closed on high-pollution days
- Use a HEPA air purifier in main living areas
- Check AirNow.gov before outdoor exercise
San Ysidro vs. Nearby California Cities
How San Ysidro's air quality compares to nearby cities:
| City | AQI | Category | Population |
|---|---|---|---|
| San Ysidro | 59 | Moderate | 1,385,617 |
| Coronado | 73 | Moderate | 1,385,379 |
| La Jolla | 73 | Moderate | 1,385,379 |
| National City | 81 | Moderate | 1,385,379 |
ZIP Codes in San Ysidro
San Ysidro covers 2 ZIP codes. Air quality can vary by neighborhood based on proximity to highways, industrial areas, and green spaces. Check your specific ZIP code for localized data.
Data Sources
- Air quality: EPA AirNow — real-time and historical AQI data
- Wildfire risk: FEMA National Risk Index
- Mold risk: Derived from EPA, FEMA, Census ACS (humidity, housing age, flood history)
- Monthly AQI: EPA Air Quality Statistics
Updated daily.