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. Portsmouth's average AQI of 44 falls in the "Good" range.

Air Quality by ZIP Code in Portsmouth

AQI varies across Portsmouth's 4 ZIP codes based on proximity to pollution sources and local geography.

ZIP Code	AQI	Category	Wildfire	Mold
03801	44	Good	12	61	View report →
03802	44	Good	12	43	View report →
03803	44	Good	12	38	View report →
03804	44	Good	12	38	View report →

Air Quality Overview

Portsmouth, New Hampshire has good air quality with an average AQI of 44. 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 Portsmouth

AQI varies across Portsmouth's 4 ZIP codes based on proximity to pollution sources, traffic patterns, and local geography:

Wildfire Smoke Risk

Portsmouth has an elevated wildfire smoke risk with an average smoke risk score of 12 (scale 0-100). There have been 4 fires recorded within 100 km of city ZIP codes.

Metric	Value
Avg. smoke risk score	12
Max smoke risk score	12
Fires within 100 km	4
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

Portsmouth has an average mold risk score of 45 out of 100, with 1 ZIP codes in the high-risk category.

Factor	Value
Mold risk score	45/100
Average humidity	69% RH
High-risk ZIPs	1
Peak season	summer 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 44), Portsmouth 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

Portsmouth vs. Nearby New Hampshire Cities

How Portsmouth's air quality compares to nearby cities:

ZIP Codes in Portsmouth

Portsmouth covers 4 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.