What Is the Air Quality in Frederick, Maryland?
Frederick, Maryland has an Air Quality Grade of B (good) with a 5-year median AQI of 42. The dominant pollutant is Ground-Level Ozone, and air quality has been stable over the past decade.
Frederick, Maryland Air Quality Snapshot
| Air Quality Grade | B65/100 |
| 5-Year Median AQI | 42 (Good) |
| Most Recent Median AQI (2023) | 44 (Good) |
| Dominant Pollutant | Ground-Level Ozone |
| 10-Year Trend | Stable (-0.10 AQI/yr) |
| Unhealthy Days (last 5 yr) | 9 |
| National Rank (cleanest = #1) | #609 of 1,020 (60th most polluted percentile) |
| Maryland Rank | #13 of 16 |
What Does the B Grade Mean?
Frederick, Maryland 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 42. Sensitive groups will see occasional caution days, but the typical resident will not need to change behavior based on air quality.
Frederick, Maryland's 5-year median AQI of 42 is right around the national average of 41 across the 1,020 monitored U.S. cities tracked here. Within Maryland, Frederick, Maryland's air quality is roughly typical for the state, where the average city posts a 5-year median AQI of 41.
For context within Maryland: Howard, Maryland currently holds the state's cleanest grade (B, AQI 37), while Baltimore, Maryland sits at the bottom (C, AQI 45).
What's in Frederick, Maryland's Air?
The dominant pollutant in Frederick, Maryland 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 | 232 | 100% |
Is the Air Getting Better or Worse?
Air quality in Frederick, Maryland 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, Frederick, Maryland posted a median AQI of 42. By 2023 that figure was 44 — a rise of 2 AQI points dirtier across 10 years of EPA records.
Year-by-Year AQI in Frederick, Maryland
| Year | Median AQI | Good Days | Unhealthy Days | Dominant Pollutant |
|---|---|---|---|---|
| 2014 | 42 | 171 | 0 | Ozone |
| 2015 | 44 | 160 | 1 | Ozone |
| 2016 | 43 | 151 | 3 | Ozone |
| 2017 | 42 | 190 | 2 | Ozone |
| 2018 | 41 | 204 | 0 | Ozone |
| 2019 | 44 | 198 | 1 | Ozone |
| 2020 | 40 | 217 | 0 | Ozone |
| 2021 | 41 | 207 | 1 | Ozone |
| 2022 | 41 | 212 | 1 | Ozone |
| 2023 | 44 | 167 | 6 | Ozone |
Health Context for Frederick, Maryland
Across the past five years, this area has logged just 9 days where AQI rose into the "Unhealthy for Sensitive Groups" range or worse — about 2 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.
Frederick, Maryland has an Air Quality Grade of B (good) with a 5-year median AQI of 42. The dominant pollutant is Ground-Level Ozone, 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.