Median AQI
63
Moderate
Texas · County air quality · 2025
Harris County, Texas
Median AQI 63 (Moderate). 8.8% of monitored days rated Good, direct from EPA Air Quality System stations.
- 63
- Median AQI
- 8.8%
- Good-air days
- 7
- Unhealthy days
- 0%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Harris County's air is moderate on balance, among the most polluted counties nationally, a median AQI of 63 with 8.8% of 274 monitored days in the Good band, driven mainly by PM2.5.
- 63
- median AQI · Moderate
- 8.8%
- days rated Good
- PM2.5
- main pollutant
- 0%
- cleaner than US counties
7 days reached Unhealthy or worse; the worst single reading hit AQI 172.
Data updated July 2026
- Good · 24 d · 8.8%
- Moderate · 223 d · 81.4%
- USG · 20 d · 7.3%
- Unhealthy · 7 d · 2.6%
How did Harris County's air break down in 2025?
Across 274 monitored days, 24 fell in the Good band (AQI 0–50) and 7 reached Unhealthy or worse. The worst single day peaked at AQI 172 (Unhealthy).
EPA AQS →Air quality data from EPA Air Quality System (2025). 274 days monitored. Median AQI: 63 (Moderate).
Insights: Harris County, Texas. EPA monitors recorded a median Air Quality Index of 63 across 274 measured days in 2025, earning a Moderate classification and a Very Poor health grade. Of those days, 24 (9%) fell in the Good band (AQI 0–50), 223 (81%) registered Moderate readings, and 20 (7%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 100, while the worst single-day peak hit 172 (Unhealthy). Residents averaged about 2.6 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (172 days), Ozone (81 days), PM10 (19 days), NO2 (1 days), CO (1 days). Across the 2020–2025 trend window, good days shifted by -85 and the median AQI moved +7 points, placing the multi-year trajectory at worsening. Residents and visitors experienced 7 unhealthy-or-worse days combined, periods when the EPA recommends sensitive groups limit prolonged outdoor exertion. Nearby counties show comparable readings: Atascosa (58.0% good, AQI 45); Bell (61.3% good, AQI 47); Bexar (39.8% good, AQI 53); Bowie (57.3% good, AQI 47); Brazoria (84.8% good, AQI 33); Brazos (63.4% good, AQI 43).
Air Quality Summary
Good Days
8.8%
24 of 274 monitored days
-66.2pp vs 75% target
Max AQI Recorded
172
Unhealthy
Health Grade
Very Poor
90th-pct AQI 100
Harris County, Good days share 8.8%
National avg
Share of monitored days at AQI 0-50 (Good band).
Harris County, Unhealthy-or-worse share 2.6%
National avg
Share of monitored days above AQI 150 (Unhealthy or worse). Bar maxes at 10% (worst-county ceiling).
AQI Day Breakdown (2025)
Distribution of 274 monitored days across EPA AQI categories.
Good
24
9%
Moderate
223
81%
USG
20
7%
Unhealthy
7
3%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Harris County.
- PM2.5 · 172 days · 62.8%
- Ozone · 81 days · 29.6%
- PM10 · 19 days · 6.9%
- NO₂ · 1 days · 0.4%
- CO · 1 days · 0.4%
Health Impact Assessment
Very Poor
Harris County's air quality is rated Very Poor based on 8.8% good air days. There were 7 unhealthy days in 2025 when outdoor activity should be limited.
Air quality is acceptable most days, but 20 days reached "Unhealthy for Sensitive Groups" (AQI 101-150) and peak AQI reached 172. Sensitive groups should monitor real-time conditions at AirNow.gov.
The dominant pollutant is PM2.5, driving AQI on 172 of 274 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Harris County. Best year: 2020 (109 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 109 | 240 | 15 | 2 | 56 | 190 |
| 2021 | 64 | 276 | 18 | 7 | 58 | 179 |
| 2022 | 57 | 281 | 22 | 5 | 60 | 179 |
| 2023 | 44 | 273 | 38 | 9 | 64 | 205 |
| 2024 | 50 | 269 | 33 | 13 | 61 | 201 |
| 2025 | 24 | 223 | 20 | 7 | 63 | 172 |
How does Harris County compare?
How Harris County compares
Good-day share worse than US avg
Harris County 8.8%
Atascosa County, Texas 58.0%
US average 76.5%
Median AQI worse than US avg
Harris County 63
Atascosa County, Texas 45
US average 38
Unhealthy days / yr worse than US avg
Harris County 7
Atascosa County, Texas 0
US average 0
Other Counties in Texas
Air quality comparison for nearby counties in Texas.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Harris County.
Clark County, Nevada
AQI 64 · 25.6% good
Imperial County, California
AQI 64 · 27.4% good
Kern County, California
AQI 61 · 23.8% good
Pinal County, Arizona
AQI 66 · 24.6% good
Bernalillo County, New Mexico
AQI 59 · 23.7% good
Tulare County, California
AQI 59 · 29.7% good
What Harris County's air means for you
On most days the air here is fine, but PM2.5 drives 7 unhealthy-or-worse days a year that sensitive groups should plan around.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-PM2.5 days, the guide explains what a median of 63 means for exposure. Health guidance
- See how Harris County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Harris County with its Texas neighbours before drawing a conclusion about the region. All of Texas
Based on 274 EPA-monitored days in 2025; figures reflect only days the monitors reported. Source: EPA Air Quality System annual summaries.
More Air Quality Data
Air Quality Guides
Frequently Asked Questions
What is the air quality in Harris County, Texas? ▼
Harris County has a median Air Quality Index (AQI) of 63, rated "Moderate." 8.8% of monitored days (24 out of 274) had good air quality in 2025.
What is the main pollutant in Harris County? ▼
The primary pollutant in Harris County is Fine Particles (PM2.5), which was the main AQI driver on 172 days (63% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does Harris County have? ▼
In 2025, Harris County recorded 7 unhealthy air days (7 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 172.
Is the air quality in Harris County getting better or worse? ▼
Air quality in Harris County is worsening based on 5-year trends (2020-2025). Best year: 2020 with 109 good days. Worst year: 2025 with 24 good days.
What does AQI 63 mean for health? ▼
Harris County's median AQI of 63 falls in the "Moderate" category. See the <a href="/guides/understanding-aqi" class="underline">AQI category guide</a> for what each range means for health.
How does Harris County compare to other counties in Texas? ▼
Harris County has 8.8% good air days. Nearby counties in Texas: Atascosa (58.0% good), Bell (61.3% good), Bexar (39.8% good), Bowie (57.3% good), Brazoria (84.8% good), Brazos (63.4% good).
What is the 90th percentile AQI in Harris County? ▼
The 90th percentile AQI for Harris County is 100, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 172 (Unhealthy).
Data Sources
Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by County dataset, 2020–2025 (aqs.epa.gov). For current conditions (not shown here — this page is historical annual data), see EPA AirNow (airnow.gov). See our methodology for how AQI, median, and coverage figures are computed.
Informational only, not professional advice. Data from EPA AQS. See our disclaimer.
Every figure on PlainAir is rendered directly from EPA AQS air-quality monitoring data, no number is typed in by an editor. This page draws directly on EPA AQS air-quality monitoring data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.