Median AQI
31
Good
New York · County air quality · 2025
Nassau County, New York
Median AQI 31 (Good). 100.0% of monitored days rated Good, direct from EPA Air Quality System stations.
- 31
- Median AQI
- 100.0%
- Good-air days
- 0
- Unhealthy days
- 96%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Nassau County's air is good on balance, among the cleanest 5% of US counties, a median AQI of 31 with 100.0% of 1 monitored days in the Good band, driven mainly by PM2.5.
- 31
- median AQI · Good
- 100.0%
- days rated Good
- PM2.5
- main pollutant
- 96%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 31.
Data updated July 2026
- Good · 1 d · 100.0%
How did Nassau County's air break down in 2025?
Across 1 monitored days, 1 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 31 (Good).
EPA AQS →Air quality data from EPA Air Quality System (2025). 1 days monitored. Median AQI: 31 (Good).
Insights: Nassau County, New York. EPA monitors recorded a median Air Quality Index of 31 across 1 measured days in 2025, earning a Good classification and a Excellent health grade. Of those days, 1 (100%) fell in the Good band (AQI 0–50), 0 (0%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 31, while the worst single-day peak hit 31 (Good). Residents averaged about 30.0 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (1 days). Across the 2020–2025 trend window, good days shifted by -316 and the median AQI moved +4 points, placing the multi-year trajectory at improving. The worst single reading over the 2020–2025 window was AQI 31, good but never Unhealthy. Nearby counties show comparable readings: Albany (67.4% good, AQI 39); Bronx (56.6% good, AQI 47); Chautauqua (88.6% good, AQI 39); Dutchess (92.7% good, AQI 37); Erie (61.3% good, AQI 44); Essex (79.8% good, AQI 42).
Air Quality Summary
Good Days
100.0%
1 of 1 monitored days
25.0pp vs 75% target
Max AQI Recorded
31
Good
Health Grade
Excellent
90th-pct AQI 31
Nassau County, Good days share 100.0%
National avg
Share of monitored days at AQI 0-50 (Good band).
Nassau County, Unhealthy-or-worse share 0.0%
National avg
Share of monitored days above AQI 150 (Unhealthy or worse). Bar maxes at 10% (worst-county ceiling).
AQI Day Breakdown (2025)
Distribution of 1 monitored days across EPA AQI categories.
Good
1
100%
Moderate
0
0%
USG
0
0%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Nassau County.
- PM2.5 · 1 days · 100.0%
Health Impact Assessment
Excellent
Nassau County's air quality is rated Excellent based on 100.0% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 100.0% of monitored days in 2025, with a median AQI of 31. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is PM2.5, driving AQI on 1 of 1 monitored days.
5-Year Air Quality Trend
Air quality is improving in Nassau County. Best year: 2020 (317 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 317 | 44 | 0 | 0 | 27 | 75 |
| 2021 | 291 | 68 | 1 | 0 | 32 | 118 |
| 2022 | 303 | 58 | 0 | 0 | 29 | 68 |
| 2023 | 275 | 86 | 1 | 3 | 31 | 197 |
| 2024 | 308 | 58 | 0 | 0 | 31 | 71 |
| 2025 | 1 | 0 | 0 | 0 | 31 | 31 |
How does Nassau County compare?
How Nassau County compares
Good-day share better than US avg
Nassau County 100.0%
Albany County, New York 67.4%
US average 76.5%
Median AQI better than US avg
Nassau County 31
Albany County, New York 39
US average 38
Unhealthy days / yr about average
Nassau County 0
Albany County, New York 0
US average 0
Other Counties in New York
Air quality comparison for nearby counties in New York.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Nassau County.
Bannock County, Idaho
AQI 31 · 91.5% good
Clark County, Washington
AQI 31 · 89.3% good
Erie County, Pennsylvania
AQI 31 · 81.4% good
Honolulu County, Hawaii
AQI 31 · 95.0% good
Josephine County, Oregon
AQI 31 · 76.2% good
Monroe County, Wisconsin
AQI 31 · 75.2% good
What Nassau County's air means for you
The air here stays in the breathable range year-round, with PM2.5 the main thing to watch.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-PM2.5 days, the guide explains what a median of 31 means for exposure. Health guidance
- See how Nassau County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Nassau County with its New York neighbours before drawing a conclusion about the region. All of New York
Based on 1 EPA-monitored days in 2025; figures reflect only days the monitors reported. Source: EPA Air Quality System annual summaries.
More Air Quality Data
Air Quality Guides
Frequently Asked Questions
What is the air quality in Nassau County, New York? ▼
Nassau County has a median Air Quality Index (AQI) of 31, rated "Good." 100.0% of monitored days (1 out of 1) had good air quality in 2025.
What is the main pollutant in Nassau County? ▼
The primary pollutant in Nassau County is Fine Particles (PM2.5), which was the main AQI driver on 1 days (100% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does Nassau County have? ▼
In 2025, Nassau County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 31.
Is the air quality in Nassau County getting better or worse? ▼
Air quality in Nassau County is improving based on 5-year trends (2020-2025). Best year: 2020 with 317 good days. Worst year: 2025 with 1 good days.
What does AQI 31 mean for health? ▼
Nassau County's median AQI of 31 falls in the "Good" category. See the <a href="/guides/understanding-aqi" class="underline">AQI category guide</a> for what each range means for health.
How does Nassau County compare to other counties in New York? ▼
Nassau County has 100.0% good air days. Nearby counties in New York: Albany (67.4% good), Bronx (56.6% good), Chautauqua (88.6% good), Dutchess (92.7% good), Erie (61.3% good), Essex (79.8% good).
What is the 90th percentile AQI in Nassau County? ▼
The 90th percentile AQI for Nassau County is 31, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 31 (Good).
Data Sources
Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by County dataset, 2020–2025 (aqs.epa.gov). For current conditions (not shown here — this page is historical annual data), see EPA AirNow (airnow.gov). See our methodology for how AQI, median, and coverage figures are computed.
Informational only, not professional advice. Data from EPA AQS. See our disclaimer.
Every figure on PlainAir is rendered directly from EPA AQS air-quality monitoring data, no number is typed in by an editor. This page draws directly on EPA AQS air-quality monitoring data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.