Air Quality in Palo Alto, CA: Good (39 AQI)
AQI 39 · Good · Ozone · Updated 2026-05-03
Palo Alto's air quality is good. Air pollution poses little or no risk.
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. Palo Alto's average AQI of 39 falls in the "Good" 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 Map: Palo Alto, CA
Each dot represents a ZIP code. Color indicates AQI level. Tap a dot for details.
Air Quality by ZIP Code in Palo Alto
AQI varies across Palo Alto's 6 ZIP codes based on proximity to pollution sources and local geography.
| ZIP Code | AQI | Category | Wildfire | Mold | |
|---|---|---|---|---|---|
| 94301 | 39 | Good | 23 | 49 | View report → |
| 94302 | 39 | Good | 23 | 12 | View report → |
| 94303 | 39 | Good | 23 | 46 | View report → |
| 94304 | 39 | Good | 23 | 20 | View report → |
| 94306 | 39 | Good | 23 | 37 | View report → |
| 94309 | 39 | Good | 23 | 12 | View report → |
Air Quality Overview
Palo Alto, California has good air quality with an average AQI of 39. This means air pollution poses little or no risk. The dominant pollutant measured 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 Palo Alto
AQI varies across Palo Alto's 6 ZIP codes based on proximity to pollution sources, traffic patterns, and local geography:
| ZIP Code | AQI | Category | Wildfire Risk | Mold Score |
|---|---|---|---|---|
| 94301 | 39 | Good | 23 | 49 |
| 94302 | 39 | Good | 23 | 12 |
| 94303 | 39 | Good | 23 | 46 |
| 94304 | 39 | Good | 23 | 20 |
| 94306 | 39 | Good | 23 | 37 |
| 94309 | 39 | Good | 23 | 12 |
Wildfire Smoke Risk
Palo Alto has an elevated wildfire smoke risk with an average smoke risk score of 23 (scale 0-100). There have been 19 fires recorded within 100 km of city ZIP codes.
| Metric | Value |
|---|---|
| Avg. smoke risk score | 23 |
| Max smoke risk score | 23 |
| Fires within 100 km | 19 |
| High-risk ZIP codes | 0 |
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
Palo Alto has an average mold risk score of 29 out of 100.
| Factor | Value |
|---|---|
| Mold risk score | 29/100 |
| 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 good air quality (AQI 39), Palo Alto residents can enjoy outdoor activities without significant restrictions. General tips:
- Monitor AQI during wildfire season for temporary spikes
- Use HEPA air purifiers indoors if you have respiratory conditions
- Maintain indoor humidity between 30-50% to prevent mold
Palo Alto vs. Nearby California Cities
How Palo Alto's air quality compares to nearby cities:
| City | AQI | Category | Population |
|---|---|---|---|
| Palo Alto | 39 | Good | 70,020 |
| Lodi | 44 | Good | 69,927 |
| Robbins | 68 | Moderate | 70,256 |
| Yuba City | 56 | Moderate | 70,671 |
ZIP Codes in Palo Alto
Palo Alto covers 6 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.