What Is the Air Quality in Marion, Indiana?
Marion, Indiana has an Air Quality Grade of C (fair) with a 5-year median AQI of 57. The dominant pollutant is Fine Particulate Matter (PM2.5), and air quality has been stable over the past decade.
Marion, Indiana Air Quality Snapshot
| Air Quality Grade | C51/100 |
| 5-Year Median AQI | 57 (Moderate) |
| Most Recent Median AQI (2023) | 60 (Moderate) |
| Dominant Pollutant | Fine Particulate Matter (PM2.5) |
| 10-Year Trend | Stable (+0.24 AQI/yr) |
| Unhealthy Days (last 5 yr) | 50 |
| National Rank (cleanest = #1) | #1003 of 1,020 (98th most polluted percentile) |
| Indiana Rank | #36 of 36 |
What Does the C Grade Mean?
Marion, Indiana earns a C — air quality is fair, but not great. With a 5-year median AQI of 57, the city sees a meaningful number of "Moderate" days each year, when the EPA flags air as a concern for unusually sensitive people.
Marion, Indiana's 5-year median AQI of 57 is 16 points above the national average of 41 — meaningfully more polluted than the typical U.S. metro tracked here. Within Indiana, Marion, Indiana runs more polluted than the state average of 41 — local sources or geography are concentrating pollution above the state's typical reading.
For context within Indiana: Floyd, Indiana currently holds the state's cleanest grade (A, AQI 36), while Clark, Indiana sits at the bottom (C, AQI 50).
What's in Marion, Indiana's Air?
The dominant pollutant in Marion, Indiana is Fine Particulate Matter (PM2.5). Fine particulate matter — particles less than 2.5 micrometers across — comes mostly from combustion: vehicle exhaust, wildfire smoke, residential wood burning, and industrial emissions. Because these particles are small enough to enter the bloodstream, PM2.5 is the pollutant most strongly linked to cardiovascular disease, respiratory illness, and premature death.
Days by Dominant Pollutant (2023)
| Pollutant | Days as Dominant | Share of Year |
|---|---|---|
| Fine Particulate Matter (PM2.5) | 310 | 85% |
| Ground-Level Ozone | 55 | 15% |
Is the Air Getting Better or Worse?
Air quality in Marion, Indiana 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, Marion, Indiana posted a median AQI of 58. By 2023 that figure was 60 — a rise of 2 AQI points dirtier across 10 years of EPA records.
Year-by-Year AQI in Marion, Indiana
| Year | Median AQI | Good Days | Unhealthy Days | Dominant Pollutant |
|---|---|---|---|---|
| 2014 | 58 | 85 | 7 | PM2.5 |
| 2015 | 56 | 129 | 3 | PM2.5 |
| 2016 | 55 | 111 | 11 | PM2.5 |
| 2017 | 54 | 134 | 4 | PM2.5 |
| 2018 | 55 | 105 | 11 | PM2.5 |
| 2019 | 58 | 78 | 4 | PM2.5 |
| 2020 | 55 | 110 | 6 | PM2.5 |
| 2021 | 58 | 81 | 6 | PM2.5 |
| 2022 | 56 | 101 | 13 | PM2.5 |
| 2023 | 60 | 84 | 21 | PM2.5 |
Health Context for Marion, Indiana
Across the past five years, this area has logged 50 days where AQI rose into the "Unhealthy for Sensitive Groups" range or worse — about 10 days per year. That is roughly typical for a U.S. metro, with most caution days clustered in summer (ozone) or wildfire season.
Healthy adults can continue normal outdoor activity in most weather, but should pay attention to AQI alerts during the worst pollution windows. People with asthma, heart disease, or pregnancy should reduce prolonged or intense outdoor exertion on flagged days, and consider running an indoor HEPA air cleaner during peak season. Because PM2.5 penetrates deep into the lungs and bloodstream, an N95 or KN95 mask provides meaningful protection on smoky or high-particulate days — surgical masks do not.
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.
Marion, Indiana has an Air Quality Grade of C (fair) with a 5-year median AQI of 57. The dominant pollutant is Fine Particulate Matter (PM2.5), and air quality has been stable over the past decade.
The data source behind this answer is the EPA Air Quality System (AQS). Every figure on the page traces back to that source; the methodology page describes the inputs and the refresh cadence in full detail.
For readers turning this answer into action: cross-reference against the underlying the EPA Air Quality System (AQS) record before acting on time-sensitive decisions. The site renders the data as it was published; subsequent revisions can shift the picture, and the live federal data is always the authoritative current reference.
Source: EPA Outdoor Air Quality Data, 2026.