Union, Illinois Air Quality
Union has a median AQI of 43, earning an air quality grade of A- — excellent air quality that ranks better than 39% of US cities. Air quality has remained relatively stable over the past decade. Ground-level ozone is the primary concern, typically peaking on warm sunny days due to vehicle and industrial emissions. In 2025, Union recorded 180 good air quality days (66% of monitored days) and 12 unhealthy days.
Population: 624 • County: McHenry
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Quick Facts
| Current AQI | 11 — Good |
| Air Quality Grade | A- |
| Median AQI (2025) | 43 |
| vs. U.S. Cities | Better than 39% |
| Primary Pollutant | Ozone |
| Unhealthy Days/Year | 12 |
| 10-Year Trend | → Stable |
| Data Source | EPA AirNow |
Health Recommendation
Air quality is satisfactory, and air pollution poses little or no risk.
It's a great day to be active outside!
5-Day AQI Forecast
Last 30 Days
Current Pollutant Levels
Real-time data from EPA AirNow
AQI Trend (10 Years)
Air Quality Days by Year
2025 Air Quality Summary
Primary Pollutant Days (2025)
Days when each pollutant was the primary driver of AQI. Learn about pollutants →
Frequently Asked Questions About Union Air Quality
What is the air quality in Union today?
The current AQI in Union is 11, which is rated "Good". Air quality is satisfactory, and air pollution poses little or no risk.
Is air quality in Union getting better or worse?
Air quality in Union has remained relatively stable over the past decade, with a median AQI of around 43.
What is the most common air pollutant in Union?
Ozone is the primary air pollutant in Union, responsible for the most air quality-impacted days in 2025. Ground-level ozone forms when sunlight reacts with vehicle and industrial emissions on warm days.
How many unhealthy air days does Union have per year?
In 2025, Union had 12 days when air quality was unhealthy or unhealthy for sensitive groups (AQI above 100). There were 180 good days and 80 moderate days out of 272 days monitored.
What air quality grade does Union receive?
Union receives an air quality grade of A-, placing it better than 39% of US cities. This grade is based on a median AQI of 43 for 2025, derived from EPA monitoring data.
Air Quality Grade
Better than 39% of US cities
Nearby Cities
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National Rankings
See how Union compares to every other US city by air quality.
Best Air Quality Cities →All city rankingsRecommended Air Purifiers for Union
Based on your area's air quality (median AQI: 43), we recommend these air purifiers to help protect your health indoors.
RabbitAir MinusA2
Stylish wall-mountable design with customizable artwork panels.
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Other Great Options
Molekule Air Pro
Commercial-grade with patented PECO technology for destroying pollutants.
Blueair Blue Pure 211+
High performance for large rooms with simple operation.
Dyson Pure Cool TP04
Premium all-in-one air purifier and fan with advanced features.
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Read our complete buying guide →