Median AQI
37
Good
New Jersey · County air quality · 2025
Monmouth County, New Jersey
Median AQI 37 (Good). 92.4% of monitored days rated Good, direct from EPA Air Quality System stations.
- 37
- Median AQI
- 92.4%
- Good-air days
- 2
- Unhealthy days
- 81%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Monmouth County's air is good on balance, cleaner than most US counties, a median AQI of 37 with 92.4% of 145 monitored days in the Good band, driven mainly by Ozone.
- 37
- median AQI · Good
- 92.4%
- days rated Good
- Ozone
- main pollutant
- 81%
- cleaner than US counties
2 days reached Unhealthy or worse; the worst single reading hit AQI 161.
Data updated July 2026
- Good · 134 d · 92.4%
- Moderate · 7 d · 4.8%
- USG · 2 d · 1.4%
- Unhealthy · 2 d · 1.4%
How did Monmouth County's air break down in 2025?
Across 145 monitored days, 134 fell in the Good band (AQI 0–50) and 2 reached Unhealthy or worse. The worst single day peaked at AQI 161 (Unhealthy).
EPA AQS →Air quality data from EPA Air Quality System (2025). 145 days monitored. Median AQI: 37 (Good).
Insights: Monmouth County, New Jersey. EPA monitors recorded a median Air Quality Index of 37 across 145 measured days in 2025, earning a Good classification and a Excellent health grade. Of those days, 134 (92%) fell in the Good band (AQI 0–50), 7 (5%) registered Moderate readings, and 2 (1%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 49, while the worst single-day peak hit 161 (Unhealthy). Residents averaged about 27.7 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (145 days). Across the 2020–2025 trend window, good days shifted by -75 and the median AQI moved +0 points, placing the multi-year trajectory at stable. Residents and visitors experienced 2 unhealthy-or-worse days combined, periods when the EPA recommends sensitive groups limit prolonged outdoor exertion. Nearby counties show comparable readings: Atlantic (79.6% good, AQI 38); Bergen (71.1% good, AQI 40); Camden (69.4% good, AQI 44); Cumberland (73.0% good, AQI 42); Gloucester (72.4% good, AQI 43); Hudson (74.7% good, AQI 41).
Air Quality Summary
Good Days
92.4%
134 of 145 monitored days
17.4pp vs 75% target
Max AQI Recorded
161
Unhealthy
Health Grade
Excellent
90th-pct AQI 49
Monmouth County, Good days share 92.4%
National avg
Share of monitored days at AQI 0-50 (Good band).
Monmouth County, Unhealthy-or-worse share 1.4%
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 145 monitored days across EPA AQI categories.
Good
134
92%
Moderate
7
5%
USG
2
1%
Unhealthy
2
1%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Monmouth County.
- Ozone · 145 days · 100.0%
Health Impact Assessment
Excellent
Monmouth County's air quality is rated Excellent based on 92.4% good air days. There were 2 unhealthy days in 2025 when outdoor activity should be limited.
Air quality is acceptable most days, but 2 days reached "Unhealthy for Sensitive Groups" (AQI 101-150) and peak AQI reached 161. Sensitive groups should monitor real-time conditions at AirNow.gov.
The dominant pollutant is Ozone, driving AQI on 145 of 145 monitored days.
5-Year Air Quality Trend
Air quality is stable in Monmouth County. Best year: 2024 (240 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 209 | 17 | 0 | 0 | 37 | 93 |
| 2021 | 227 | 24 | 3 | 1 | 36 | 154 |
| 2022 | 226 | 20 | 1 | 1 | 38 | 161 |
| 2023 | 210 | 35 | 2 | 0 | 39 | 140 |
| 2024 | 240 | 23 | 1 | 0 | 37 | 119 |
| 2025 | 134 | 7 | 2 | 2 | 37 | 161 |
How does Monmouth County compare?
How Monmouth County compares
Good-day share better than US avg
Monmouth County 92.4%
Atlantic County, New Jersey 79.6%
US average 76.5%
Median AQI better than US avg
Monmouth County 37
Atlantic County, New Jersey 38
US average 38
Unhealthy days / yr worse than US avg
Monmouth County 2
Atlantic County, New Jersey 0
US average 0
Other Counties in New Jersey
Air quality comparison for nearby counties in New Jersey.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Monmouth County.
Alachua County, Florida
AQI 37 · 90.1% good
Beltrami County, Minnesota
AQI 37 · 88.8% good
Benewah County, Idaho
AQI 37 · 74.6% good
Brevard County, Florida
AQI 37 · 89.7% good
Brown County, Indiana
AQI 37 · 94.5% good
Brown County, Wisconsin
AQI 37 · 79.0% good
What Monmouth County's air means for you
On most days the air here is fine, but Ozone drives 2 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-Ozone days, the guide explains what a median of 37 means for exposure. Health guidance
- See how Monmouth County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Monmouth County with its New Jersey neighbours before drawing a conclusion about the region. All of New Jersey
Based on 145 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 Monmouth County, New Jersey? ▼
Monmouth County has a median Air Quality Index (AQI) of 37, rated "Good." 92.4% of monitored days (134 out of 145) had good air quality in 2025.
What is the main pollutant in Monmouth County? ▼
The primary pollutant in Monmouth County is Ozone (O3), which was the main AQI driver on 145 days (100% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Monmouth County have? ▼
In 2025, Monmouth County recorded 2 unhealthy air days (2 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 161.
Is the air quality in Monmouth County getting better or worse? ▼
Air quality in Monmouth County is stable based on 5-year trends (2020-2025). Best year: 2024 with 240 good days. Worst year: 2025 with 134 good days.
What does AQI 37 mean for health? ▼
Monmouth County's median AQI of 37 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 Monmouth County compare to other counties in New Jersey? ▼
Monmouth County has 92.4% good air days. Nearby counties in New Jersey: Atlantic (79.6% good), Bergen (71.1% good), Camden (69.4% good), Cumberland (73.0% good), Gloucester (72.4% good), Hudson (74.7% good).
What is the 90th percentile AQI in Monmouth County? ▼
The 90th percentile AQI for Monmouth County is 49, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 161 (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.