AIR QUALITY CA

Air Quality in Mill Valley, CA: Good (40 AQI)

AQI 40 · Good · Ozone · Updated 2026-05-03

Mill Valley's air quality is good. Air pollution poses little or no risk.

Data: EPA AirNow, FEMA National Risk Index Last verified: 2026-05-03

Average AQI

Good

AQI Category

Wildfire Risk

Mold Score

ZIP Codes

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. Mill Valley's average AQI of 40 falls in the "Good" range.

Air Quality by ZIP Code in Mill Valley

AQI varies across Mill Valley's 2 ZIP codes based on proximity to pollution sources and local geography.

ZIP Code	AQI	Category	Wildfire	Mold
94941	40	Good	18	46	View report →
94942	40	Good	18	16	View report →

Air Quality Overview

Mill Valley, California has good air quality with an average AQI of 40. 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 Mill Valley

AQI varies across Mill Valley's 2 ZIP codes based on proximity to pollution sources, traffic patterns, and local geography:

ZIP Code	AQI	Category	Wildfire Risk	Mold Score
94941	40	Good	18	46
94942	40	Good	18	16

Wildfire Smoke Risk

Mill Valley has an elevated wildfire smoke risk with an average smoke risk score of 18 (scale 0-100). There have been 12 fires recorded within 100 km of city ZIP codes.

Metric	Value
Avg. smoke risk score	18
Max smoke risk score	18
Fires within 100 km	12
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

Mill Valley has an average mold risk score of 31 out of 100.

Factor	Value
Mold risk score	31/100
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 40), Mill Valley 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

Mill Valley vs. Nearby California Cities

How Mill Valley's air quality compares to nearby cities:

City	AQI	Category	Population
Mill Valley	40	Good	186,895
Corte Madera	42	Good	186,895
San Quentin	42	Good	186,895
Guasti	118	USG	185,010

ZIP Codes in Mill Valley

Mill Valley 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.

Frequently Asked Questions

Is the air safe to breathe in Mill Valley?

Yes — Mill Valley's average AQI is 40 (Good). Air pollution poses little or no risk for the general population.

How many unhealthy air days does Mill Valley have?

Mill Valley has zero recorded unhealthy air quality days, which is excellent. Air quality can still vary seasonally due to wildfire smoke, pollen, or industrial activity.

What is the AQI in Mill Valley?

The average Air Quality Index (AQI) in Mill Valley is 40, categorized as Good. The primary pollutant is Ozone. AQI ranges from 0-500, where 0-50 is Good, 51-100 Moderate, 101-150 Unhealthy for Sensitive Groups, and 151+ Unhealthy.

What is the wildfire risk in Mill Valley?

Mill Valley has a wildfire risk score of 18 out of 100. Low wildfire risk means smoke events are uncommon, but regional fires can still temporarily affect air quality.

Is mold a concern in Mill Valley?

Mill Valley has a mold risk score of 31 out of 100, based on humidity, precipitation, and temperature data. Maintain good ventilation and address any water intrusion promptly to prevent mold growth.

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