Median AQI
43
Good
North Carolina · County air quality · 2025
Guilford County, North Carolina
Median AQI 43 (Good). 74.4% of monitored days rated Good, direct from EPA Air Quality System stations.
- 43
- Median AQI
- 74.4%
- Good-air days
- 0
- Unhealthy days
- 40%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Guilford County's air is good on balance, more polluted than the median US county, a median AQI of 43 with 74.4% of 273 monitored days in the Good band, driven mainly by PM2.5.
- 43
- median AQI · Good
- 74.4%
- days rated Good
- PM2.5
- main pollutant
- 40%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 77.
Data updated July 2026
- Good · 203 d · 74.4%
- Moderate · 70 d · 25.6%
How did Guilford County's air break down in 2025?
Across 273 monitored days, 203 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 77 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 273 days monitored. Median AQI: 43 (Good).
Insights: Guilford County, North Carolina. EPA monitors recorded a median Air Quality Index of 43 across 273 measured days in 2025, earning a Good classification and a Moderate health grade. Of those days, 203 (74%) fell in the Good band (AQI 0–50), 70 (26%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 56, while the worst single-day peak hit 77 (Moderate). Residents averaged about 22.3 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (164 days), Ozone (108 days), PM10 (1 days). Across the 2020–2025 trend window, good days shifted by -85 and the median AQI moved +3 points, placing the multi-year trajectory at worsening. The worst single reading over the 2020–2025 window was AQI 77, moderate but never Unhealthy. Nearby counties show comparable readings: Alexander (92.4% good, AQI 39); Avery (93.9% good, AQI 38); Buncombe (71.4% good, AQI 42); Caldwell (96.2% good, AQI 37); Carteret (94.2% good, AQI 37); Caswell (94.6% good, AQI 39).
Air Quality Summary
Good Days
74.4%
203 of 273 monitored days
-0.6pp vs 75% target
Max AQI Recorded
77
Moderate
Health Grade
Moderate
90th-pct AQI 56
Guilford County, Good days share 74.4%
National avg
Share of monitored days at AQI 0-50 (Good band).
Guilford County, Unhealthy-or-worse share 0.0%
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 273 monitored days across EPA AQI categories.
Good
203
74%
Moderate
70
26%
USG
0
0%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Guilford County.
- PM2.5 · 164 days · 60.1%
- Ozone · 108 days · 39.6%
- PM10 · 1 days · 0.4%
Health Impact Assessment
Moderate
Guilford County's air quality is rated Moderate based on 74.4% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 74.4% of monitored days in 2025, with a median AQI of 43. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is PM2.5, driving AQI on 164 of 273 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Guilford County. Best year: 2020 (288 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 288 | 77 | 0 | 0 | 40 | 88 |
| 2021 | 245 | 120 | 0 | 0 | 44 | 100 |
| 2022 | 223 | 142 | 0 | 0 | 46 | 84 |
| 2023 | 183 | 178 | 4 | 0 | 50 | 131 |
| 2024 | 249 | 116 | 1 | 0 | 44 | 122 |
| 2025 | 203 | 70 | 0 | 0 | 43 | 77 |
How does Guilford County compare?
How Guilford County compares
Good-day share worse than US avg
Guilford County 74.4%
Alexander County, North Carolina 92.4%
US average 76.5%
Median AQI worse than US avg
Guilford County 43
Alexander County, North Carolina 39
US average 38
Unhealthy days / yr about average
Guilford County 0
Alexander County, North Carolina 0
US average 0
Other Counties in North Carolina
Air quality comparison for nearby counties in North Carolina.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Guilford County.
Allegan County, Michigan
AQI 43 · 71.2% good
Allen County, Ohio
AQI 43 · 65.9% good
Ashtabula County, Ohio
AQI 43 · 81.2% good
Bell County, Kentucky
AQI 43 · 63.5% good
Boise County, Idaho
AQI 43 · 72.9% good
Brazos County, Texas
AQI 43 · 63.4% good
What Guilford County's air means for you
The air here stays in the breathable range year-round, with PM2.5 the main thing to watch.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-PM2.5 days, the guide explains what a median of 43 means for exposure. Health guidance
- See how Guilford County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Guilford County with its North Carolina neighbours before drawing a conclusion about the region. All of North Carolina
Based on 273 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 Guilford County, North Carolina? ▼
Guilford County has a median Air Quality Index (AQI) of 43, rated "Good." 74.4% of monitored days (203 out of 273) had good air quality in 2025.
What is the main pollutant in Guilford County? ▼
The primary pollutant in Guilford County is Fine Particles (PM2.5), which was the main AQI driver on 164 days (60% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does Guilford County have? ▼
In 2025, Guilford County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 77.
Is the air quality in Guilford County getting better or worse? ▼
Air quality in Guilford County is worsening based on 5-year trends (2020-2025). Best year: 2020 with 288 good days. Worst year: 2023 with 183 good days.
What does AQI 43 mean for health? ▼
Guilford County's median AQI of 43 falls in the "Good" category. See the <a href="/guides/understanding-aqi" class="underline">AQI category guide</a> for what each range means for health.
How does Guilford County compare to other counties in North Carolina? ▼
Guilford County has 74.4% good air days. Nearby counties in North Carolina: Alexander (92.4% good), Avery (93.9% good), Buncombe (71.4% good), Caldwell (96.2% good), Carteret (94.2% good), Caswell (94.6% good).
What is the 90th percentile AQI in Guilford County? ▼
The 90th percentile AQI for Guilford County is 56, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 77 (Moderate).
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.