Bad Air Days in Harris County, Texas: 29 a Year
29 bad air days a year
Among the worst tenth of monitored US counties. Ranked 15 of 996 monitored counties, where 1 is worst.
What makes them bad: mostly ozone: summer smog (6% particle days).
The bad-air season here
- J
- F
- M
- A
- M
- J
- J
- A
- S
- O
- N
- D
Most bad days here fall in September and August and June and October and May. Averaged over 2016 to 2025.
Is a purifier worth it here?
- 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.
- Sign up for EnviroFlash ozone alerts for this area during the worst months.
Better or worse than it was
In 2000 to 2009 this county averaged 58 bad days a year; in 2016 to 2025, 29. The air has improved. The worst recent year was 2023, with 48 bad days on 365 monitored days.
| Date | AQI | Main pollutant |
|---|---|---|
| 2023-05-18 | 205 | Ozone |
| 2018-07-27 | 204 | Ozone |
| 2019-08-15 | 202 | Ozone |
| 2024-06-07 | 201 | Ozone |
| 2024-08-21 | 200 | Ozone |
The air on a normal day
Across 3,653 monitored days from 2016 to 2025, the air in Harris County rated Good on 21% of them, less often than the 72% typical of monitored counties, and Moderate on 71%. The median day sat at AQI 58; one day in ten went above 93.
The pollutant setting the AQI on an ordinary day here:
- fine particles (PM2.5)69%2,514 days
- ozone26%964 days
- coarse dust (PM10)3%111 days
- nitrogen dioxide2%64 days
Every recent year on file
| Year | Days monitored | Good | Moderate | Over 100 | Over 150 | Median AQI | Highest AQI |
|---|---|---|---|---|---|---|---|
| 2025* | 365 | 40 | 287 | 38 | 10 | 62 | 172 |
| 2024 | 366 | 50 | 269 | 47 | 14 | 61 | 201 |
| 2023 | 365 | 44 | 273 | 48 | 10 | 64 | 205 |
| 2022 | 365 | 57 | 281 | 27 | 5 | 60 | 179 |
| 2021 | 365 | 64 | 276 | 25 | 7 | 58 | 179 |
| 2020 | 366 | 109 | 240 | 17 | 2 | 56 | 190 |
| 2019 | 365 | 91 | 247 | 27 | 5 | 56 | 202 |
| 2018 | 365 | 102 | 236 | 27 | 8 | 56 | 204 |
| 2017 | 365 | 107 | 238 | 20 | 2 | 54 | 177 |
| 2016 | 366 | 118 | 231 | 17 | 1 | 55 | 159 |
| 2015 | 365 | 88 | 238 | 39 | 12 | 58 | 203 |
| 2014 | 365 | 68 | 289 | 8 | 1 | 58 | 151 |
| 2013 | 365 | 78 | 268 | 19 | 2 | 57 | 197 |
| 2012 | 366 | 51 | 280 | 35 | 8 | 59 | 217 |
| 2011 | 365 | 42 | 278 | 45 | 10 | 60 | 190 |
| 2010 | 365 | 57 | 270 | 38 | 11 | 60 | 179 |
*2025 may be a partial year in EPA's file.
Elsewhere in Texas
- El Paso County26/yr
- Tarrant County19/yr
- Denton County17/yr
- Dallas County12/yr
- Collin County11/yr
- Bexar County11/yr
- Cameron County9/yr
- Montgomery County8/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.