Median AQI
42
Good
North Carolina · County air quality · 2025
Johnston County, North Carolina
Median AQI 42 (Good). 76.6% of monitored days rated Good, direct from EPA Air Quality System stations.
- 42
- Median AQI
- 76.6%
- Good-air days
- 0
- Unhealthy days
- 43%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Johnston County's air is good on balance, more polluted than the median US county, a median AQI of 42 with 76.6% of 273 monitored days in the Good band, driven mainly by PM2.5.
- 42
- median AQI · Good
- 76.6%
- days rated Good
- PM2.5
- main pollutant
- 43%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 84.
Data updated July 2026
- Good · 209 d · 76.6%
- Moderate · 64 d · 23.4%
How did Johnston County's air break down in 2025?
Across 273 monitored days, 209 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 84 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 273 days monitored. Median AQI: 42 (Good).
Insights: Johnston County, North Carolina. EPA monitors recorded a median Air Quality Index of 42 across 273 measured days in 2025, earning a Good classification and a Good health grade. Of those days, 209 (77%) fell in the Good band (AQI 0–50), 64 (23%) 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 84 (Moderate). Residents averaged about 23.0 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (194 days), Ozone (79 days). Across the 2020–2025 trend window, good days shifted by -57 and the median AQI moved +3 points, placing the multi-year trajectory at stable. The worst single reading over the 2020–2025 window was AQI 84, 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
76.6%
209 of 273 monitored days
1.6pp vs 75% target
Max AQI Recorded
84
Moderate
Health Grade
Good
90th-pct AQI 56
Johnston County, Good days share 76.6%
National avg
Share of monitored days at AQI 0-50 (Good band).
Johnston 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
209
77%
Moderate
64
23%
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 Johnston County.
- PM2.5 · 194 days · 71.1%
- Ozone · 79 days · 28.9%
Health Impact Assessment
Good
Johnston County's air quality is rated Good based on 76.6% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 76.6% of monitored days in 2025, with a median AQI of 42. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is PM2.5, driving AQI on 194 of 273 monitored days.
5-Year Air Quality Trend
Air quality is stable in Johnston County. Best year: 2022 (271 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 266 | 73 | 0 | 0 | 39 | 75 |
| 2021 | 240 | 125 | 0 | 0 | 44 | 97 |
| 2022 | 271 | 93 | 1 | 0 | 42 | 140 |
| 2023 | 240 | 124 | 1 | 0 | 44 | 115 |
| 2024 | 261 | 104 | 0 | 0 | 43 | 84 |
| 2025 | 209 | 64 | 0 | 0 | 42 | 84 |
How does Johnston County compare?
How Johnston County compares
Good-day share about average
Johnston County 76.6%
Alexander County, North Carolina 92.4%
US average 76.5%
Median AQI worse than US avg
Johnston County 42
Alexander County, North Carolina 39
US average 38
Unhealthy days / yr about average
Johnston 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 Johnston County.
Adams County, Pennsylvania
AQI 42 · 73.8% good
Anderson County, Tennessee
AQI 42 · 91.0% good
Andrew County, Missouri
AQI 42 · 84.3% good
Armstrong County, Pennsylvania
AQI 42 · 68.1% good
Baldwin County, Alabama
AQI 42 · 72.2% good
Belmont County, Ohio
AQI 42 · 63.0% good
What Johnston 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 42 means for exposure. Health guidance
- See how Johnston County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Johnston 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 Johnston County, North Carolina? ▼
Johnston County has a median Air Quality Index (AQI) of 42, rated "Good." 76.6% of monitored days (209 out of 273) had good air quality in 2025.
What is the main pollutant in Johnston County? ▼
The primary pollutant in Johnston County is Fine Particles (PM2.5), which was the main AQI driver on 194 days (71% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does Johnston County have? ▼
In 2025, Johnston County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 84.
Is the air quality in Johnston County getting better or worse? ▼
Air quality in Johnston County is stable based on 5-year trends (2020-2025). Best year: 2022 with 271 good days. Worst year: 2025 with 209 good days.
What does AQI 42 mean for health? ▼
Johnston County's median AQI of 42 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 Johnston County compare to other counties in North Carolina? ▼
Johnston County has 76.6% 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 Johnston County? ▼
The 90th percentile AQI for Johnston County is 56, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 84 (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.