What Is the Air Quality in Harford, Maryland?
Harford, Maryland has an Air Quality Grade of B (good) with a 5-year median AQI of 44. The dominant pollutant is Fine Particulate Matter (PM2.5), and air quality has been improving over the past decade.
Harford, Maryland Air Quality Snapshot
| Air Quality Grade | B66/100 |
| 5-Year Median AQI | 44 (Good) |
| Most Recent Median AQI (2023) | 45 (Good) |
| Dominant Pollutant | Fine Particulate Matter (PM2.5) |
| 10-Year Trend | Improving (-0.75 AQI/yr) |
| Unhealthy Days (last 5 yr) | 29 |
| National Rank (cleanest = #1) | #708 of 1,020 (69th most polluted percentile) |
| Maryland Rank | #15 of 16 |
What Does the B Grade Mean?
Harford, 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 44. Sensitive groups will see occasional caution days, but the typical resident will not need to change behavior based on air quality.
Harford, Maryland's 5-year median AQI of 44 is 3 points above the national average of 41 — meaningfully more polluted than the typical U.S. metro tracked here. Within Maryland, Harford, Maryland 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 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 Harford, Maryland's Air?
The dominant pollutant in Harford, Maryland 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 |
|---|---|---|
| Ground-Level Ozone | 189 | 53% |
| Fine Particulate Matter (PM2.5) | 170 | 47% |
Is the Air Getting Better or Worse?
Air quality in Harford, Maryland has been improving over the past decade, with median AQI dropping by roughly 0.8 points per year. That is consistent with the broader national pattern — most U.S. metros have seen steady reductions in particulate and ozone pollution since the 2010s as cleaner vehicles and power plants come online.
In 2014, Harford, Maryland posted a median AQI of 52. By 2023 that figure was 45 — a drop of 7 AQI points cleaner across 10 years of EPA records.
Year-by-Year AQI in Harford, Maryland
| Year | Median AQI | Good Days | Unhealthy Days | Dominant Pollutant |
|---|---|---|---|---|
| 2014 | 52 | 161 | 3 | PM2.5 |
| 2015 | 48 | 198 | 6 | PM2.5 |
| 2016 | 48 | 211 | 12 | PM2.5 |
| 2017 | 47 | 206 | 9 | PM2.5 |
| 2018 | 42 | 247 | 10 | PM2.5 |
| 2019 | 45 | 229 | 9 | Ozone |
| 2020 | 41 | 286 | 1 | Ozone |
| 2021 | 46 | 219 | 9 | PM2.5 |
| 2022 | 43 | 262 | 0 | Ozone |
| 2023 | 45 | 238 | 10 | Ozone |
Health Context for Harford, Maryland
Across the past five years, this area has logged 29 days where AQI rose into the "Unhealthy for Sensitive Groups" range or worse — about 6 days per year. That is roughly typical for a U.S. metro, with most caution days clustered in summer (ozone) or wildfire season.
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 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.
Harford, Maryland has an Air Quality Grade of B (good) with a 5-year median AQI of 44. The dominant pollutant is Fine Particulate Matter (PM2.5), and air quality has been improving 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.
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.