Bad Air Days in Montgomery County, Pennsylvania: 4 a Year
4 bad air days a year
About the middle of monitored US counties. Ranked 314 of 996 monitored counties, where 1 is worst.
What makes them bad: mostly ozone: summer smog (20% particle days).
When the bad days come in Montgomery
- J
- F
- M
- A
- M
- J
- J
- A
- S
- O
- N
- D
Most bad days here fall in June and July and May. Averaged over 2016 to 2025.
Is a purifier worth it here?
- Bad air days are rare here. A standard furnace filter is enough; no purifier needed for outdoor air.
- On the odd bad day, check AirNow and keep windows shut.
Better or worse than it was
In 2000 to 2009 this county averaged 25 bad days a year; in 2016 to 2025, 4. The air has improved. The worst recent year was 2018, with 7 bad days on 352 monitored days.
| Date | AQI | Main pollutant |
|---|---|---|
| 2023-06-07 | 284 | PM2.5 |
| 2023-06-08 | 229 | PM2.5 |
| 2023-06-29 | 165 | PM2.5 |
| 2023-06-06 | 154 | PM2.5 |
| 2023-06-30 | 153 | PM2.5 |
Most days, not the worst ones
Across 3,574 monitored days from 2016 to 2025, the air in Montgomery County rated Good on 69% of them, close to the 72% typical of monitored counties, and Moderate on 30%. The median day sat at AQI 42; one day in ten went above 63.
The pollutant setting the AQI on an ordinary day here:
- ozone51%1,832 days
- fine particles (PM2.5)49%1,742 days
Year by year
| Year | Days monitored | Good | Moderate | Over 100 | Over 150 | Median AQI | Highest AQI |
|---|---|---|---|---|---|---|---|
| 2025* | 365 | 268 | 96 | 1 | 0 | 41 | 133 |
| 2024 | 365 | 266 | 98 | 1 | 0 | 40 | 140 |
| 2023 | 365 | 232 | 127 | 6 | 5 | 44 | 284 |
| 2022 | 362 | 237 | 124 | 1 | 0 | 44 | 108 |
| 2021 | 356 | 202 | 148 | 6 | 0 | 47 | 150 |
| 2020 | 366 | 269 | 97 | 0 | 0 | 43 | 99 |
| 2019 | 362 | 262 | 99 | 1 | 0 | 40 | 129 |
| 2018 | 352 | 242 | 103 | 7 | 0 | 41 | 129 |
| 2017 | 364 | 210 | 147 | 7 | 0 | 47 | 129 |
| 2016 | 317 | 266 | 46 | 5 | 0 | 34 | 140 |
| 2015 | 365 | 206 | 153 | 6 | 0 | 47 | 133 |
| 2014 | 365 | 210 | 149 | 6 | 0 | 47 | 122 |
| 2013 | 365 | 201 | 158 | 6 | 0 | 48 | 115 |
| 2012 | 366 | 178 | 180 | 8 | 0 | 51 | 126 |
| 2011 | 365 | 147 | 202 | 16 | 1 | 54 | 151 |
| 2010 | 346 | 165 | 163 | 18 | 1 | 52 | 159 |
*2025 may be a partial year in EPA's file.
Nearby counties on file
- Allegheny County12/yr
- Philadelphia County9/yr
- Bucks County8/yr
- Warren Countythin data
- Lancaster County6/yr
- Berks County5/yr
- Delaware County4/yr
- Northampton 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, and on why a purifier does not touch ozone in smoke vs ozone.