Median AQI
34
Good
New York · County air quality · 2025
Hamilton County, New York
Median AQI 34 (Good). 97.2% of monitored days rated Good, direct from EPA Air Quality System stations.
- 34
- Median AQI
- 97.2%
- Good-air days
- 0
- Unhealthy days
- 97%
- Cleaner than US counties
Hamilton County's 2025 annual median AQI is 34 (Good), with 97.2% Good days
According to the U.S. EPA Air Quality System, Hamilton County, New York posted a 2025 median AQI of 34 (Good) across 355 monitored days, with 97.2% rated Good and 0 unhealthy or worse. This is an annual comparison, not today's advisory.
Data source EPA Air Quality System (AQS)
- Cleaner than US
- Hamilton County's 97.2% Good-day share places it cleaner than 97% of US counties in 2025.
- Closest median-AQI peer
- Androscoggin County (85.2% Good, median AQI 34) is the closest nationwide median-AQI peer to Hamilton County.
- 2020–2025 trend
- Hamilton County's floor-qualifying Good-day share is stable from 2020 to 2025 (99.2% → 97.2%).
- Median AQI
- Median AQI: 34
The verdict
According to EPA Air Quality System monitoring data, Hamilton County's air is good on balance, among the cleanest 5% of US counties, a median AQI of 34 with 97.2% of 355 monitored days in the Good band, driven mainly by Ozone.
- 34
- median AQI · Good
- 97.2%
- days rated Good
- Ozone
- main pollutant
- 97%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 87.
Annual release change
What changed in the 2025 EPA annual release
- Hamilton County's peak single-day AQI rose from 74 to 87 between the 2024 and 2025 EPA annual releases, a change of +13 points.
Data updated August 2026
- Good · 345 d · 97.2%
- Moderate · 10 d · 2.8%
How did Hamilton County's air break down in 2025?
Across 355 monitored days, 345 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 87 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 355 days monitored. Median AQI: 34 (Good).
Insights: Hamilton County, New York. EPA monitors recorded a median Air Quality Index of 34 across 355 measured days in 2025, earning a Good classification and a Excellent health grade. Of those days, 345 (97%) fell in the Good band (AQI 0–50), 10 (3%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 44, while the worst single-day peak hit 87 (Moderate). Residents averaged about 29.2 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (355 days). Across the 2020–2025 trend window, the share of monitored days rated Good shifted by -2.0 points and the median AQI moved +0 points, placing the multi-year trajectory at stable. The worst single reading over the 2020–2025 window was AQI 87, moderate but never Unhealthy. Nearby counties show comparable readings: Albany (68.5% good, AQI 39); Bronx (59.2% good, AQI 45); Chautauqua (89.0% good, AQI 36); Dutchess (94.0% good, AQI 34); Erie (63.8% good, AQI 44); Essex (83.8% good, AQI 41).
Air Quality Summary
Good Days
97.2%
345 of 355 monitored days
22.2pp vs 75% target
Max AQI Recorded
87
Moderate
Health Grade
Excellent
90th-pct AQI 44
Hamilton County, Good days share 97.2%
National avg
Share of monitored days at AQI 0-50 (Good band).
Hamilton 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 355 monitored days across EPA AQI categories.
Good
345
97%
Moderate
10
3%
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 Hamilton County.
- Ozone · 355 days · 100.0%
Health Impact Assessment
Excellent
Hamilton County's air quality is rated Excellent based on 97.2% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 97.2% of monitored days in 2025, with a median AQI of 34. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 355 of 355 monitored days.
5-Year Air Quality Trend
Air quality is stable in Hamilton County. Highest Good-day share: 2020 (99.2%, 354 of 357 monitored days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 354 | 3 | 0 | 0 | 34 | 54 |
| 2021 | 343 | 15 | 0 | 0 | 33 | 100 |
| 2022 | 345 | 5 | 0 | 0 | 34 | 71 |
| 2023 | 337 | 17 | 0 | 0 | 33 | 90 |
| 2024 | 340 | 8 | 0 | 0 | 33 | 74 |
| 2025 | 345 | 10 | 0 | 0 | 34 | 87 |
How does Hamilton County compare?
How Hamilton County compares
Good-day share better than typical
Hamilton County 97.2%
Androscoggin County, Maine 85.2%
Typical US county 76.0%
Median AQI better than typical
Hamilton County 34
Androscoggin County, Maine 34
Typical US county 39
Unhealthy days / yr better than typical
Hamilton County 0
Androscoggin County, Maine 0
Typical US county 1
Counties with a similar median AQI
Nationwide peers within about the same annual median AQI as Hamilton County (34), not geographic neighbors.
Androscoggin County, Maine
Median AQI 34 · 85.2% Good-day share
Archuleta County, Colorado
Median AQI 34 · 83.0% Good-day share
Bristol City County, Virginia
Median AQI 34 · 78.0% Good-day share
Brown County, Indiana
Median AQI 34 · 95.9% Good-day share
Clark County, Arkansas
Median AQI 34 · 96.7% Good-day share
Clay County, South Dakota
Median AQI 34 · 87.8% Good-day share
Same primary pollutant: Ozone
Ozone led the AQI on the most monitored days here. These peers share that driver and the closest Good-day share (a second relationship type beyond median-AQI neighbors).
Caldwell County, North Carolina
97.1% Good-day share · median AQI 36
Claiborne County, Tennessee
97.3% Good-day share · median AQI 35
Honolulu County, Hawaii
97.3% Good-day share · median AQI 29
Oswego County, New York
97.3% Good-day share · median AQI 34
Greenup County, Kentucky
96.9% Good-day share · median AQI 36
Meade County, South Dakota
97.4% Good-day share · median AQI 36
New York counties on the map
Geographic containment only, other monitored counties in New York, independent of AQI or pollutant match.
What Hamilton County's air means for you
The air here stays in the breathable range year-round, with Ozone the main thing to watch.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-Ozone days, the guide explains what a median of 34 means for exposure. Health guidance
- See how Hamilton County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Hamilton County with its New York neighbours before drawing a conclusion about the region. All of New York
Based on 355 EPA-monitored days in 2025; figures reflect only days the monitors reported. Source: EPA Air Quality System annual summaries.
Keep exploring the annual AQI record
Air-quality reading list
Frequently Asked Questions
What is the air quality in Hamilton County, New York? ▼
Hamilton County has a median Air Quality Index (AQI) of 34, rated "Good." 97.2% of monitored days (345 out of 355) had good air quality in 2025.
What is the main pollutant in Hamilton County? ▼
The primary pollutant in Hamilton County is Ozone (O3), which was the main AQI driver on 355 days (100% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Hamilton County have? ▼
In 2025, Hamilton County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 87.
Is the air quality in Hamilton County getting better or worse? ▼
Air quality in Hamilton County is stable across floor-qualifying years (2020-2025); years with fewer than 100 monitored days are excluded from that direction. Highest qualifying Good-day share: 2020 at 99.2% (354 of 357 days). Lowest qualifying Good-day share: 2023 at 95.2% (337 of 354 days).
What does AQI 34 mean for health? ▼
Hamilton County's median AQI of 34 falls in the "Good" category. See the AQI category guide for what each range means for health.
How does Hamilton County compare to other counties in New York? ▼
Hamilton County has 97.2% good air days. Nearby counties in New York: Albany (68.5% good), Bronx (59.2% good), Chautauqua (89.0% good), Dutchess (94.0% good), Erie (63.8% good), Essex (83.8% good).
What is the 90th percentile AQI in Hamilton County? ▼
The 90th percentile AQI for Hamilton County is 44, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 87 (Moderate).
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. Spotted a figure that looks wrong? Report a correction.
Source: U.S. EPA Air Quality System (AQS) Annual AQI by county summary files for Hamilton County, New York · 2020–2025
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Every figure on PlainAirData 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.