What Is the Air Quality in Delaware, Ohio?
Delaware, Ohio has an Air Quality Grade of B (good) with a 5-year median AQI of 39. The dominant pollutant is Ground-Level Ozone, and air quality has been stable over the past decade.
Delaware, Ohio Air Quality Snapshot
| Air Quality Grade | B68/100 |
| 5-Year Median AQI | 39 (Good) |
| Most Recent Median AQI (2023) | 41 (Good) |
| Dominant Pollutant | Ground-Level Ozone |
| 10-Year Trend | Stable (-0.16 AQI/yr) |
| Unhealthy Days (last 5 yr) | 2 |
| National Rank (cleanest = #1) | #418 of 1,020 (41th cleanest percentile) |
| Ohio Rank | #12 of 40 |
What Does the B Grade Mean?
Delaware, Ohio earns a B — air quality is reliably in the safe range for most residents most of the time, with a 5-year median AQI of 39. Sensitive groups will see occasional caution days, but the typical resident will not need to change behavior based on air quality.
Delaware, Ohio's 5-year median AQI of 39 is 2 points below the national average of 41 — meaningfully cleaner than the typical U.S. metro tracked here. Within Ohio, Delaware, Ohio's air quality is roughly typical for the state, where the average city posts a 5-year median AQI of 40.
For context within Ohio: Columbiana, Ohio currently holds the state's cleanest grade (A, AQI 12), while Butler, Ohio sits at the bottom (D, AQI 50).
What's in Delaware, Ohio's Air?
The dominant pollutant in Delaware, Ohio is Ground-Level Ozone. Ground-level ozone forms when sunlight reacts with vehicle exhaust and industrial emissions. It is worst on hot, sunny, stagnant summer days. Ozone irritates the lungs, triggers asthma attacks, and reduces lung function — even healthy adults can feel chest tightness and shortness of breath after exercising in elevated ozone.
Days by Dominant Pollutant (2023)
| Pollutant | Days as Dominant | Share of Year |
|---|---|---|
| Ground-Level Ozone | 245 | 100% |
Is the Air Getting Better or Worse?
Air quality in Delaware, Ohio has held roughly steady over the past decade, with year-to-year shifts in median AQI of less than half a point. That stability makes the city's long-run grade a reliable signal of what residents can expect day-to-day.
In 2014, Delaware, Ohio posted a median AQI of 41. By 2023 that figure was 41 — a flat reading of 0 AQI points across 10 years of EPA records.
Year-by-Year AQI in Delaware, Ohio
| Year | Median AQI | Good Days | Unhealthy Days | Dominant Pollutant |
|---|---|---|---|---|
| 2014 | 41 | 188 | 2 | Ozone |
| 2015 | 39 | 187 | 1 | Ozone |
| 2016 | 41 | 179 | 1 | Ozone |
| 2017 | 38 | 228 | 0 | Ozone |
| 2018 | 39 | 212 | 0 | Ozone |
| 2019 | 41 | 214 | 0 | Ozone |
| 2020 | 38 | 222 | 1 | Ozone |
| 2021 | 38 | 222 | 0 | Ozone |
| 2022 | 37 | 230 | 0 | Ozone |
| 2023 | 41 | 211 | 1 | Ozone |
Health Context for Delaware, Ohio
Across the past five years, this area has logged just 2 days where AQI rose into the "Unhealthy for Sensitive Groups" range or worse — about 0 days per year, or roughly one every other month. That is a low count by national standards.
For most healthy adults, current air quality in this area does not require any change in behavior. People with severe asthma, COPD, or recent cardiac events should still keep an eye on daily AQI alerts, especially during wildfire season. Because ozone peaks in the afternoon on hot sunny days, plan outdoor exercise for early morning or after sunset on bad-air days.
How This Grade Is Calculated
The AirHistory Air Quality Grade combines four signals: the 5-year median AQI (40% of the score), the 10-year trend direction (30%), the count of unhealthy days per year (20%), and the dominant pollutant type (10%). All four come directly from the EPA Air Quality System (AQS), which aggregates readings from federally certified monitors. Read the full methodology.
Delaware, Ohio has an Air Quality Grade of B (good) with a 5-year median AQI of 39. The dominant pollutant is Ground-Level Ozone, and air quality has been stable over the past decade.
This answer pulls from the EPA Air Quality System (AQS), the authoritative federal source for U.S. air quality and pollution monitoring. The headline number above is the direct answer; what follows is the additional context most readers need to use the answer for a real decision rather than just a fact lookup.
A practical caveat: the headline answer above reflects the most recent the EPA Air Quality System (AQS) vintage; underlying data is often revised for months after first publication, and the right reference for any specific decision is whichever vintage is current at the time of the decision. The as-of date is stamped on every page.
Source: EPA Outdoor Air Quality Data, 2026.