Median AQI
41
Good
North Carolina · County air quality · 2025
Johnston County, North Carolina
Median AQI 41 (Good). 77.5% of monitored days rated Good, direct from EPA Air Quality System stations.
- 41
- Median AQI
- 77.5%
- Good-air days
- 0
- Unhealthy days
- 50%
- Cleaner than US counties
Johnston County's 2025 annual median AQI is 41 (Good), with 77.5% Good days
According to the U.S. EPA Air Quality System, Johnston County, North Carolina posted a 2025 median AQI of 41 (Good) across 365 monitored days, with 77.5% rated Good and 0 unhealthy or worse. This is an annual comparison, not today's advisory.
Data source EPA Air Quality System (AQS)
- Cleaner than US
- Johnston County's 77.5% Good-day share places it cleaner than 50% of US counties in 2025.
- Closest median-AQI peer
- Armstrong County (70.5% Good, median AQI 41) is the closest nationwide median-AQI peer to Johnston County.
- 2020–2025 trend
- Johnston County's floor-qualifying Good-day share is stable from 2020 to 2025 (78.5% → 77.5%).
- Median AQI
- Median AQI: 41
The verdict
According to EPA Air Quality System monitoring data, Johnston County's air is good on balance, cleaner than the median US county, a median AQI of 41 with 77.5% of 365 monitored days in the Good band, driven mainly by PM2.5.
- 41
- median AQI · Good
- 77.5%
- days rated Good
- PM2.5
- main pollutant
- 50%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 84.
Annual release change
What changed in the 2025 EPA annual release
- Johnston County's Good-day share rose from 71.5% to 77.5% between the 2024 and 2025 EPA annual releases, a change of +6.0 percentage points.
Data updated August 2026
- Good · 283 d · 77.5%
- Moderate · 82 d · 22.5%
How did Johnston County's air break down in 2025?
Across 365 monitored days, 283 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). 365 days monitored. Median AQI: 41 (Good).
Insights: Johnston County, North Carolina. EPA monitors recorded a median Air Quality Index of 41 across 365 measured days in 2025, earning a Good classification and a Good health grade. Of those days, 283 (78%) fell in the Good band (AQI 0–50), 82 (22%) 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 23.3 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (243 days), Ozone (122 days). Across the 2020–2025 trend window, the share of monitored days rated Good shifted by -0.9 points (measured against 339 monitored days in 2020 and 365 in 2025, so raw day counts are not comparable) and the median AQI moved +2 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 (93.5% good, AQI 38); Avery (92.3% good, AQI 38); Buncombe (73.4% good, AQI 40); Caldwell (97.1% good, AQI 36); Carteret (96.2% good, AQI 35); Caswell (95.1% good, AQI 37).
Air Quality Summary
Good Days
77.5%
283 of 365 monitored days
2.5pp vs 75% target
Max AQI Recorded
84
Moderate
Health Grade
Good
90th-pct AQI 56
Johnston County, Good days share 77.5%
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 365 monitored days across EPA AQI categories.
Good
283
78%
Moderate
82
22%
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 · 243 days · 66.6%
- Ozone · 122 days · 33.4%
Health Impact Assessment
Good
Johnston County's air quality is rated Good based on 77.5% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 77.5% of monitored days in 2025, with a median AQI of 41. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is PM2.5, driving AQI on 243 of 365 monitored days.
5-Year Air Quality Trend
Air quality is stable in Johnston County. Highest Good-day share: 2020 (78.5%, 266 of 339 monitored 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 | 283 | 82 | 0 | 0 | 41 | 84 |
How does Johnston County compare?
How Johnston County compares
Good-day share better than typical
Johnston County 77.5%
Armstrong County, Pennsylvania 70.5%
Typical US county 76.0%
Median AQI worse than typical
Johnston County 41
Armstrong County, Pennsylvania 41
Typical US county 39
Unhealthy days / yr better than typical
Johnston County 0
Armstrong County, Pennsylvania 0
Typical US county 1
Counties with a similar median AQI
Nationwide peers within about the same annual median AQI as Johnston County (41), not geographic neighbors.
Armstrong County, Pennsylvania
Median AQI 41 · 70.5% Good-day share
Benewah County, Idaho
Median AQI 41 · 63.4% Good-day share
Berrien County, Michigan
Median AQI 41 · 80.9% Good-day share
Callaway County, Missouri
Median AQI 41 · 89.6% Good-day share
Cambria County, Pennsylvania
Median AQI 41 · 74.5% Good-day share
Cass County, Missouri
Median AQI 41 · 77.6% Good-day share
Same primary pollutant: PM2.5
PM2.5 led the AQI on the most monitored days here. These peers share that driver and the closest Good-day share (a second relationship type beyond median-AQI neighbors).
Pennington County, South Dakota
77.5% Good-day share · median AQI 32
Crow Wing County, Minnesota
77.8% Good-day share · median AQI 37
Warren County, Kentucky
77.8% Good-day share · median AQI 39
Kootenai County, Idaho
77.8% Good-day share · median AQI 31
Canyon County, Idaho
77.1% Good-day share · median AQI 36
Codington County, South Dakota
78.0% Good-day share · median AQI 35
North Carolina counties on the map
Geographic containment only, other monitored counties in North Carolina, independent of AQI or pollutant match.
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 41 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 365 EPA-monitored days in 2025; figures reflect only days the monitors reported. Source: EPA Air Quality System annual summaries.
Keep exploring the annual AQI record
Air-quality reading list
Frequently Asked Questions
What is the air quality in Johnston County, North Carolina? ▼
Johnston County has a median Air Quality Index (AQI) of 41, rated "Good." 77.5% of monitored days (283 out of 365) 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 243 days (67% 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 across floor-qualifying years (2020-2025); years with fewer than 100 monitored days are excluded from that direction. Highest qualifying Good-day share: 2020 at 78.5% (266 of 339 days). Lowest qualifying Good-day share: 2023 at 65.8% (240 of 365 days).
What does AQI 41 mean for health? ▼
Johnston County's median AQI of 41 falls in the "Good" category. See the AQI category guide for what each range means for health.
How does Johnston County compare to other counties in North Carolina? ▼
Johnston County has 77.5% good air days. Nearby counties in North Carolina: Alexander (93.5% good), Avery (92.3% good), Buncombe (73.4% good), Caldwell (97.1% good), Carteret (96.2% good), Caswell (95.1% 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. Spotted a figure that looks wrong? Report a correction.
Source: U.S. EPA Air Quality System (AQS) Annual AQI by county summary files for Johnston County, North Carolina · 2020–2025
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Every figure on PlainAirData 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.