Median AQI
40
Good
North Carolina · County air quality · 2025
Union County, North Carolina
Median AQI 40 (Good). 91.0% of monitored days rated Good, direct from EPA Air Quality System stations.
- 40
- Median AQI
- 91.0%
- Good-air days
- 0
- Unhealthy days
- 82%
- Cleaner than US counties
Union County's 2025 annual median AQI is 40 (Good), with 91.0% Good days
According to the U.S. EPA Air Quality System, Union County, North Carolina posted a 2025 median AQI of 40 (Good) across 245 monitored days, with 91.0% 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
- Union County's 91.0% Good-day share places it cleaner than 82% of US counties in 2025.
- Closest median-AQI peer
- Anderson County (91.3% Good, median AQI 40) is the closest nationwide median-AQI peer to Union County.
- 2020–2025 trend
- Union County's floor-qualifying Good-day share is worsening from 2020 to 2025 (100.0% → 91.0%).
- Median AQI
- Median AQI: 40
The verdict
According to EPA Air Quality System monitoring data, Union County's air is good on balance, cleaner than most US counties, a median AQI of 40 with 91.0% of 245 monitored days in the Good band, driven mainly by Ozone.
- 40
- median AQI · Good
- 91.0%
- days rated Good
- Ozone
- main pollutant
- 82%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 90.
Annual release change
What changed in the 2025 EPA annual release
- Union County's Good-day share rose from 86.5% to 91.0% between the 2024 and 2025 EPA annual releases, a change of +4.5 percentage points.
Data updated August 2026
- Good · 223 d · 91.0%
- Moderate · 22 d · 9.0%
How did Union County's air break down in 2025?
Across 245 monitored days, 223 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 90 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 245 days monitored. Median AQI: 40 (Good).
Insights: Union County, North Carolina. EPA monitors recorded a median Air Quality Index of 40 across 245 measured days in 2025, earning a Good classification and a Excellent health grade. Of those days, 223 (91%) fell in the Good band (AQI 0–50), 22 (9%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 50, while the worst single-day peak hit 90 (Moderate). Residents averaged about 27.3 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (245 days). Across the 2020–2025 trend window, the share of monitored days rated Good shifted by -9.0 points and the median AQI moved +9 points, placing the multi-year trajectory at worsening. The worst single reading over the 2020–2025 window was AQI 90, moderate but never Unhealthy. Nearby counties show comparable readings: Alexander (93.5% good, AQI 38); Avery (92.3% good, AQI 38); Buncombe (73.4% good, AQI 40); Caldwell (97.1% good, AQI 36); Carteret (96.2% good, AQI 35); Caswell (95.1% good, AQI 37).
Air Quality Summary
Good Days
91.0%
223 of 245 monitored days
16.0pp vs 75% target
Max AQI Recorded
90
Moderate
Health Grade
Excellent
90th-pct AQI 50
Union County, Good days share 91.0%
National avg
Share of monitored days at AQI 0-50 (Good band).
Union 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 245 monitored days across EPA AQI categories.
Good
223
91%
Moderate
22
9%
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 Union County.
- Ozone · 245 days · 100.0%
Health Impact Assessment
Excellent
Union County's air quality is rated Excellent based on 91.0% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 91.0% of monitored days in 2025, with a median AQI of 40. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 245 of 245 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Union County. Highest Good-day share: 2020 (100.0%, 242 of 242 monitored days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 242 | 0 | 0 | 0 | 31 | 50 |
| 2021 | 209 | 34 | 1 | 0 | 42 | 101 |
| 2022 | 218 | 26 | 0 | 0 | 41 | 100 |
| 2023 | 201 | 43 | 1 | 0 | 43 | 101 |
| 2024 | 212 | 33 | 0 | 0 | 41 | 97 |
| 2025 | 223 | 22 | 0 | 0 | 40 | 90 |
How does Union County compare?
How Union County compares
Good-day share better than typical
Union County 91.0%
Anderson County, South Carolina 91.3%
Typical US county 76.0%
Median AQI worse than typical
Union County 40
Anderson County, South Carolina 40
Typical US county 39
Unhealthy days / yr better than typical
Union County 0
Anderson County, South Carolina 0
Typical US county 1
Counties with a similar median AQI
Nationwide peers within about the same annual median AQI as Union County (40), not geographic neighbors.
Anderson County, South Carolina
Median AQI 40 · 91.3% Good-day share
Andrew County, Missouri
Median AQI 40 · 86.9% Good-day share
Anne Arundel County, Maryland
Median AQI 40 · 87.6% Good-day share
Bergen County, New Jersey
Median AQI 40 · 71.1% Good-day share
Blair County, Pennsylvania
Median AQI 40 · 76.9% Good-day share
Brazos County, Texas
Median AQI 40 · 68.5% 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).
Hancock County, Maine
91.0% Good-day share · median AQI 35
Manatee County, Florida
91.0% Good-day share · median AQI 36
Benzie County, Michigan
91.1% Good-day share · median AQI 35
Brevard County, Florida
91.2% Good-day share · median AQI 38
Mayes County, Oklahoma
91.2% Good-day share · median AQI 37
Carroll County, Indiana
90.8% Good-day share · median AQI 35
North Carolina counties on the map
Geographic containment only, other monitored counties in North Carolina, independent of AQI or pollutant match.
What Union 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 40 means for exposure. Health guidance
- See how Union County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Union County with its North Carolina neighbours before drawing a conclusion about the region. All of North Carolina
Based on 245 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 Union County, North Carolina? ▼
Union County has a median Air Quality Index (AQI) of 40, rated "Good." 91.0% of monitored days (223 out of 245) had good air quality in 2025.
What is the main pollutant in Union County? ▼
The primary pollutant in Union County is Ozone (O3), which was the main AQI driver on 245 days (100% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Union County have? ▼
In 2025, Union County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 90.
Is the air quality in Union County getting better or worse? ▼
Air quality in Union County is worsening 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 100.0% (242 of 242 days). Lowest qualifying Good-day share: 2023 at 82.0% (201 of 245 days).
What does AQI 40 mean for health? ▼
Union County's median AQI of 40 falls in the "Good" category. See the AQI category guide for what each range means for health.
How does Union County compare to other counties in North Carolina? ▼
Union County has 91.0% good air days. Nearby counties in North Carolina: Alexander (93.5% good), Avery (92.3% good), Buncombe (73.4% good), Caldwell (97.1% good), Carteret (96.2% good), Caswell (95.1% good).
What is the 90th percentile AQI in Union County? ▼
The 90th percentile AQI for Union County is 50, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 90 (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 Union County, North Carolina · 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.