Houston Air Quality in 2021
In 2021, Houston's air quality (Houston-The Woodlands-Sugar Land, TX area) had a median daily AQI of 59 (Moderate) across 365 monitored days. 30 days (8.2%) reached Unhealthy for Sensitive Groups or worse, 60 were Good, and the year's peak AQI was 179 (Unhealthy). Fine particulate matter (PM2.5) set the daily AQI on 263 of those days. The cleanest month of 2021 was December (median AQI 54, 0 days above 100) and the worst was September (median 82, 11 days above 100, peak 159).
- Good: 16.4%
- Moderate: 75.3%
- Unhealthy for Sensitive Groups: 5.8%
- Unhealthy or worse: 2.5%
Reduce Indoor Ozone in Houston
Today's main pollutant in Houston is ground-level ozone (AQI 24). Important: standard HEPA filters do NOT remove ozone — only a purifier with a substantial activated-carbon bed adsorbs it. The biggest wins are cutting indoor sources (gas appliances, certain "ionizer" purifiers) and ventilating when outdoor ozone is low (early morning). A high-carbon unit helps with the gases and VOCs that linger indoors.
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How was Houston's air quality in 2021?
Moderate on a typical day: median AQI 59, with 30 days above AQI 100 out of 365 monitored — the 2nd cleanest of 7 years on record for the area.
- ✓Peak AQI in 2021: 179 (Unhealthy).
- ✓Fine particulate matter (PM2.5) was the main pollutant on 263 days.
- ✓Cleanest month: December; worst: September.
Frequently asked questions
What was the average AQI in Houston in 2021?▾
EPA's Air Quality System puts Houston's (Houston-The Woodlands-Sugar Land, TX) median daily AQI for 2021 at 59, which is Moderate. 30 days were Unhealthy for Sensitive Groups or worse and the year's highest AQI was 179.
Which month had the worst air quality in Houston in 2021?▾
The cleanest month of 2021 was December (median AQI 54, 0 days above 100) and the worst was September (median 82, 11 days above 100, peak 159).
Was 2021 a good or bad year for Houston's air?▾
Among the 7 years EPA has published for the area (2019–2025), 2021 ranks 2nd cleanest by days above AQI 100. 2021's median of 59 is in line with the area's typical annual median of 61.
Houston month by month in 2021
Houston air quality month by month, 2021 (Houston-The Woodlands-Sugar Land, TX, EPA AQS daily AQI)
| Month | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| January | 31 | 54 | 2 | 130 | PM2.5 |
| February | 28 | 55 | 0 | 71 | PM2.5 |
| March | 31 | 57 | 0 | 95 | PM2.5 |
| April | 30 | 63 | 3 | 159 | PM2.5 |
| May | 31 | 56 | 1 | 161 | PM2.5 |
| June | 30 | 57 | 6 | 159 | PM2.5 |
| July | 31 | 63 | 2 | 179 | PM2.5 |
| August | 31 | 63 | 1 | 126 | PM2.5 |
| Septemberworst | 30 | 82 | 11 | 159 | O3 |
| October | 31 | 66 | 4 | 166 | PM2.5 |
| November | 30 | 65 | 0 | 78 | PM2.5 |
| Decembercleanest | 31 | 54 | 0 | 90 | PM2.5 |
How 2021 compares
Among the 7 years EPA has published for the area (2019–2025), 2021 ranks 2nd cleanest by days above AQI 100.
2021's median of 59 is in line with the area's typical annual median of 61.
Activity-specific thresholds: running, cycling, kids' sports.
Right now in Houston
The latest EPA AirNow observation puts Houston's AQI at 24 (O3). The figures above are multi-year annual statistics, not today's reading.
View current Houston air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (Houston-The Woodlands-Sugar Land, TX), 2019–2025. Daily AQI per CBSA is the highest AQI reported by any monitor in the area that day; the defining parameter is the pollutant that set it. Month and season statistics pool every such day in the period across all years listed. Retrieved 2026-09-09.