Bad Air Days in Allegheny County, Pennsylvania: 12 a Year
12 bad air days a year
Among the worst tenth of monitored US counties. Ranked 66 of 996 monitored counties, where 1 is worst.
What makes them bad: mostly particles: smoke and dust (63% particle days).
When the bad days come in Allegheny
- J
- F
- M
- A
- M
- J
- J
- A
- S
- O
- N
- D
Most bad days here fall in June and November and December. Averaged over 2016 to 2025.
Is a purifier worth it here?
- Particles (wildfire smoke, dust) cause enough bad days here to matter. A HEPA purifier sized to your bedroom removes them; run it with windows shut on bad days.
- Upgrade the furnace or AC filter to MERV 13 so the whole house is filtered, not just one room.
- Ozone drives many bad days here. Purifiers and filters do not remove ozone, so do not buy one for that. Ozone peaks on hot afternoons: exercise outside in the morning.
Better or worse than it was
In 2000 to 2009 this county averaged 63 bad days a year; in 2016 to 2025, 12. The air has improved. The worst recent year was 2016, with 20 bad days on 366 monitored days.
| Date | AQI | Main pollutant |
|---|---|---|
| 2023-06-29 | 237 | PM2.5 |
| 2023-06-28 | 199 | PM2.5 |
| 2017-12-03 | 168 | PM2.5 |
| 2019-02-03 | 165 | PM2.5 |
| 2019-02-04 | 164 | PM2.5 |
Most days, not the worst ones
Across 3,653 monitored days from 2016 to 2025, the air in Allegheny County rated Good on 33% of them, less often than the 72% typical of monitored counties, and Moderate on 63%. The median day sat at AQI 56; one day in ten went above 82.
The pollutant setting the AQI on an ordinary day here:
- fine particles (PM2.5)75%2,748 days
- ozone25%902 days
Allegheny County by year
| Year | Days monitored | Good | Moderate | Over 100 | Over 150 | Median AQI | Highest AQI |
|---|---|---|---|---|---|---|---|
| 2025* | 365 | 168 | 193 | 4 | 0 | 52 | 129 |
| 2024 | 366 | 175 | 182 | 9 | 0 | 52 | 129 |
| 2023 | 365 | 121 | 227 | 17 | 2 | 56 | 237 |
| 2022 | 365 | 129 | 225 | 11 | 1 | 56 | 151 |
| 2021 | 365 | 118 | 240 | 7 | 1 | 57 | 154 |
| 2020 | 366 | 138 | 218 | 10 | 0 | 54 | 128 |
| 2019 | 365 | 67 | 287 | 11 | 4 | 59 | 165 |
| 2018 | 365 | 92 | 260 | 13 | 1 | 58 | 154 |
| 2017 | 365 | 111 | 235 | 19 | 1 | 58 | 168 |
| 2016 | 366 | 103 | 243 | 20 | 1 | 56 | 152 |
| 2015 | 365 | 105 | 241 | 19 | 1 | 58 | 157 |
| 2014 | 365 | 99 | 256 | 10 | 1 | 58 | 157 |
| 2013 | 365 | 98 | 254 | 13 | 1 | 57 | 190 |
| 2012 | 366 | 76 | 246 | 44 | 4 | 61 | 172 |
| 2011 | 365 | 64 | 259 | 42 | 4 | 63 | 186 |
| 2010 | 365 | 50 | 254 | 61 | 15 | 69 | 200 |
*2025 may be a partial year in EPA's file.
Elsewhere in Pennsylvania
- Philadelphia County9/yr
- Bucks County8/yr
- Warren Countythin data
- Lancaster County6/yr
- Berks County5/yr
- Delaware County4/yr
- Northampton County4/yr
- Montgomery County4/yr
How this is counted
A bad air day is a day the county's daily AQI from EPA AirData went above 100, the level where EPA tells children, older adults and people with asthma or heart disease to cut back outdoors. Monitors do not run every day, so yearly counts are scaled to 365 days. This is the record, not today's air: for that, check AirNow. More on the method in how the county numbers are made, on the AQI 100 line in what counts as a bad air day.