Allegheny, Pennsylvania vs Cook, Illinois Air Quality
Side-by-side air quality comparison using 10 years of EPA monitoring data. Allegheny, Pennsylvania has the edge with an Air Quality Grade of C (54/100).
| Metric | Allegheny, Pennsylvania | Cook, Illinois |
|---|---|---|
| Air Quality Grade | C (54/100) | D (49/100) |
| Current Median AQI | 56 (Moderate) | 57 (Moderate) |
| 5-Year Average AQI | 56 | 57 |
| 10-Year Trend | → Stable (-2) | → Stable (-2) |
| Unhealthy Days/Year | 11 | 18 |
| Primary Pollutant | Fine Particulate Matter (PM2.5) | Fine Particulate Matter (PM2.5) |
Side-by-Side Analysis
Allegheny, Pennsylvania outperforms Cook, Illinois on overall air quality with a Grade C (54/100) versus D (49/100). Allegheny, Pennsylvania's 5-year median AQI of 56 sits in the "Moderate" range, while Cook, Illinois averages 57 ("Moderate") — a 1-point gap that shows up consistently in year-over-year readings, not just in a single year.
Both cities have held roughly stable air quality over the past decade — making the current ranking a reliable signal of what residents can expect.
What's in the Air
Both cities share the same dominant pollutant: Fine Particulate Matter (PM2.5). These cities' dominant issue is fine particulate matter — typically driven by combustion (vehicles, wildfire smoke, industry, residential wood burning). PM2.5 is the air pollutant most strongly linked to long-term cardiovascular and respiratory disease because the particles penetrate the bloodstream.
Health Implications
Over a 5-year window, Allegheny, Pennsylvania averages roughly 11 unhealthy air days per year (AQI above 100, where sensitive groups should limit outdoor exertion) versus 18 for Cook, Illinois. The two cities offer comparable counts of unhealthy days, suggesting that day-to-day exposure planning would look similar for residents of either. For long-term residents, the cleaner-air city is associated with measurably better outcomes on respiratory disease, cardiovascular events, and life expectancy — Harvard cohort research consistently finds 0.5 to 1.0 years of additional life expectancy for each 10-µg/m³ reduction in long-term PM2.5 exposure.
Frequently Asked Questions
Allegheny, Pennsylvania has better air quality with a Grade C (54/100) compared to Cook, Illinois's Grade D (49/100). Allegheny, Pennsylvania has a current median AQI of 56 and is stable over the past decade.
Allegheny, Pennsylvania averages 11 unhealthy air days per year (5-year average), while Cook, Illinois averages 18. Unhealthy days are those when AQI exceeds 100 and sensitive groups should limit outdoor activity.
Allegheny, Pennsylvania's primary pollutant is Fine Particulate Matter (PM2.5), while Cook, Illinois's is Fine Particulate Matter (PM2.5). Both cities share the same dominant pollutant.
Source: EPA Outdoor Air Quality Data, 2026.
The side-by-side above pulls the EPA Air Quality System data data for both entity A and entity B. What follows is the interpretation — which specific axes carry the most weight for entity A versus entity B, and which differences are large enough to influence a real decision.
For households or analysts using this comparison as a decision input, the right framing is usually not "which is better" in aggregate but "which is better for the specific decision in front of you." EPA Air Quality System data captures the raw data; the framing depends on whether the question is investment, residency, planning, or research.