Median AQI
39
Good
Delaware · County air quality · 2025
Sussex County, Delaware
Median AQI 39 (Good). 82.2% of monitored days rated Good, direct from EPA Air Quality System stations.
- 39
- Median AQI
- 82.2%
- Good-air days
- 0
- Unhealthy days
- 62%
- Cleaner than US counties
Sussex County's 2025 annual median AQI is 39 (Good), with 82.2% Good days
According to the U.S. EPA Air Quality System, Sussex County, Delaware posted a 2025 median AQI of 39 (Good) across 365 monitored days, with 82.2% 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
- Sussex County's 82.2% Good-day share places it cleaner than 62% of US counties in 2025.
- Closest median-AQI peer
- Aiken County (90.6% Good, median AQI 39) is the closest nationwide median-AQI peer to Sussex County.
- 2020–2025 trend
- Sussex County's floor-qualifying Good-day share is improving from 2020 to 2025 (78.1% → 82.2%).
- Median AQI
- Median AQI: 39
The verdict
According to EPA Air Quality System monitoring data, Sussex County's air is good on balance, cleaner than the median US county, a median AQI of 39 with 82.2% of 365 monitored days in the Good band, driven mainly by Ozone.
- 39
- median AQI · Good
- 82.2%
- days rated Good
- Ozone
- main pollutant
- 62%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 105.
Annual release change
What changed in the 2025 EPA annual release
- Sussex County's peak single-day AQI rose from 90 to 105 between the 2024 and 2025 EPA annual releases, a change of +15 points.
Data updated August 2026
- Good · 300 d · 82.2%
- Moderate · 64 d · 17.5%
- USG · 1 d · 0.3%
How did Sussex County's air break down in 2025?
Across 365 monitored days, 300 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 105 (USG).
EPA AQS →Air quality data from EPA Air Quality System (2025). 365 days monitored. Median AQI: 39 (Good).
Insights: Sussex County, Delaware. EPA monitors recorded a median Air Quality Index of 39 across 365 measured days in 2025, earning a Good classification and a Good health grade. Of those days, 300 (82%) fell in the Good band (AQI 0–50), 64 (18%) registered Moderate readings, and 1 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 57, while the worst single-day peak hit 105 (USG). Residents averaged about 24.7 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (269 days), PM2.5 (96 days). Across the 2020–2025 trend window, the share of monitored days rated Good shifted by +4.0 points and the median AQI moved -3 points, placing the multi-year trajectory at improving. The worst single reading over the 2020–2025 window was AQI 105, usg but never Unhealthy. Nearby counties show comparable readings: Kent (75.6% good, AQI 41); New Castle (64.4% good, AQI 44).
Air Quality Summary
Good Days
82.2%
300 of 365 monitored days
7.2pp vs 75% target
Max AQI Recorded
105
USG
Health Grade
Good
90th-pct AQI 57
Sussex County, Good days share 82.2%
National avg
Share of monitored days at AQI 0-50 (Good band).
Sussex 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
300
82%
Moderate
64
18%
USG
1
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 Sussex County.
- Ozone · 269 days · 73.7%
- PM2.5 · 96 days · 26.3%
Health Impact Assessment
Good
Sussex County's air quality is rated Good based on 82.2% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 82.2% of monitored days in 2025, with a median AQI of 39. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 269 of 365 monitored days.
5-Year Air Quality Trend
Air quality is improving in Sussex County. Highest Good-day share: 2025 (82.2%, 300 of 365 monitored days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 286 | 80 | 0 | 0 | 42 | 87 |
| 2021 | 277 | 88 | 0 | 0 | 40 | 100 |
| 2022 | 274 | 91 | 0 | 0 | 43 | 87 |
| 2023 | 215 | 144 | 3 | 2 | 47 | 203 |
| 2024 | 298 | 67 | 0 | 0 | 40 | 90 |
| 2025 | 300 | 64 | 1 | 0 | 39 | 105 |
How does Sussex County compare?
How Sussex County compares
Good-day share better than typical
Sussex County 82.2%
Aiken County, South Carolina 90.6%
Typical US county 76.0%
Median AQI about typical
Sussex County 39
Aiken County, South Carolina 39
Typical US county 39
Unhealthy days / yr better than typical
Sussex County 0
Aiken County, South Carolina 0
Typical US county 1
Counties with a similar median AQI
Nationwide peers within about the same annual median AQI as Sussex County (39), not geographic neighbors.
Aiken County, South Carolina
Median AQI 39 · 90.6% Good-day share
Albany County, New York
Median AQI 39 · 68.5% Good-day share
Anderson County, Tennessee
Median AQI 39 · 94.3% Good-day share
Bay County, Michigan
Median AQI 39 · 70.4% Good-day share
Berkeley County, West Virginia
Median AQI 39 · 83.6% Good-day share
Boyd County, Kentucky
Median AQI 39 · 80.0% Good-day share
Same primary pollutant: Ozone
Ozone 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).
Atlantic County, New Jersey
82.2% Good-day share · median AQI 36
Calaveras County, California
82.2% Good-day share · median AQI 40
Tioga County, Pennsylvania
82.1% Good-day share · median AQI 39
Horry County, South Carolina
82.5% Good-day share · median AQI 39
Middlesex County, Massachusetts
81.9% Good-day share · median AQI 38
Westchester County, New York
82.5% Good-day share · median AQI 38
Delaware counties on the map
Geographic containment only, other monitored counties in Delaware, independent of AQI or pollutant match.
What Sussex County's air means for you
The air here stays in the breathable range year-round, with Ozone the main thing to watch.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-Ozone days, the guide explains what a median of 39 means for exposure. Health guidance
- See how Sussex County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Sussex County with its Delaware neighbours before drawing a conclusion about the region. All of Delaware
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 Sussex County, Delaware? ▼
Sussex County has a median Air Quality Index (AQI) of 39, rated "Good." 82.2% of monitored days (300 out of 365) had good air quality in 2025.
What is the main pollutant in Sussex County? ▼
The primary pollutant in Sussex County is Ozone (O3), which was the main AQI driver on 269 days (74% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Sussex County have? ▼
In 2025, Sussex County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 105.
Is the air quality in Sussex County getting better or worse? ▼
Air quality in Sussex County is improving across floor-qualifying years (2020-2025); years with fewer than 100 monitored days are excluded from that direction. Highest qualifying Good-day share: 2025 at 82.2% (300 of 365 days). Lowest qualifying Good-day share: 2023 at 59.1% (215 of 365 days).
What does AQI 39 mean for health? ▼
Sussex County's median AQI of 39 falls in the "Good" category. See the AQI category guide for what each range means for health.
How does Sussex County compare to other counties in Delaware? ▼
Sussex County has 82.2% good air days. Nearby counties in Delaware: Kent (75.6% good), New Castle (64.4% good).
What is the 90th percentile AQI in Sussex County? ▼
The 90th percentile AQI for Sussex County is 57, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 105 (USG).
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 Sussex County, Delaware · 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.