Median AQI
52
Moderate
California · County air quality · 2025
Placer County, California
Median AQI 52 (Moderate). 45.8% of monitored days rated Good, direct from EPA Air Quality System stations.
- 52
- Median AQI
- 45.8%
- Good-air days
- 0
- Unhealthy days
- 5%
- Cleaner than US counties
Placer County's 2025 annual median AQI is 52 (Moderate), with 45.8% Good days
According to the U.S. EPA Air Quality System, Placer County, California posted a 2025 median AQI of 52 (Moderate) across 365 monitored days, with 45.8% 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
- Placer County's 45.8% Good-day share places it cleaner than 5% of US counties in 2025.
- Closest median-AQI peer
- Allegheny County (46.0% Good, median AQI 52) is the closest nationwide median-AQI peer to Placer County.
- 2020–2025 trend
- Placer County's floor-qualifying Good-day share is improving from 2020 to 2025 (36.1% → 45.8%).
- Median AQI
- Median AQI: 52
The verdict
According to EPA Air Quality System monitoring data, Placer County's air is moderate on balance, among the most polluted counties nationally, a median AQI of 52 with 45.8% of 365 monitored days in the Good band, driven mainly by Ozone.
- 52
- median AQI · Moderate
- 45.8%
- days rated Good
- Ozone
- main pollutant
- 5%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 143.
Annual release change
What changed in the 2025 EPA annual release
- Placer County's Good-day share fell from 51.4% to 45.8% between the 2024 and 2025 EPA annual releases, a change of -5.6 percentage points.
Data updated August 2026
- Good · 167 d · 45.8%
- Moderate · 196 d · 53.7%
- USG · 2 d · 0.5%
How did Placer County's air break down in 2025?
Across 365 monitored days, 167 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 143 (USG).
EPA AQS →Air quality data from EPA Air Quality System (2025). 365 days monitored. Median AQI: 52 (Moderate).
Insights: Placer County, California. EPA monitors recorded a median Air Quality Index of 52 across 365 measured days in 2025, earning a Moderate classification and a Poor health grade. Of those days, 167 (46%) fell in the Good band (AQI 0–50), 196 (54%) registered Moderate readings, and 2 (1%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 71, while the worst single-day peak hit 143 (USG). Residents averaged about 13.7 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (216 days), PM2.5 (149 days). Across the 2020–2025 trend window, the share of monitored days rated Good shifted by +10.2 points and the median AQI moved -5 points, placing the multi-year trajectory at improving. The worst single reading over the 2020–2025 window was AQI 143, usg but never Unhealthy. Nearby counties show comparable readings: Alameda (53.0% good, AQI 49); Amador (87.4% good, AQI 38); Butte (65.2% good, AQI 46); Calaveras (82.2% good, AQI 40); Colusa (79.2% good, AQI 40); Contra Costa (53.5% good, AQI 48).
Air Quality Summary
Good Days
45.8%
167 of 365 monitored days
-29.3pp vs 75% target
Max AQI Recorded
143
USG
Health Grade
Poor
90th-pct AQI 71
Placer County, Good days share 45.8%
National avg
Share of monitored days at AQI 0-50 (Good band).
Placer 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
167
46%
Moderate
196
54%
USG
2
1%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Placer County.
- Ozone · 216 days · 59.2%
- PM2.5 · 149 days · 40.8%
Health Impact Assessment
Poor
Placer County's air quality is rated Poor based on 45.8% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 45.8% of monitored days in 2025, with a median AQI of 52. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 216 of 365 monitored days.
5-Year Air Quality Trend
Air quality is improving in Placer County. Highest Good-day share: 2024 (51.4%, 188 of 366 monitored days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 130 | 195 | 20 | 15 | 57 | 247 |
| 2021 | 130 | 187 | 30 | 9 | 58 | 692 |
| 2022 | 156 | 185 | 15 | 4 | 54 | 442 |
| 2023 | 164 | 193 | 8 | 0 | 52 | 143 |
| 2024 | 188 | 151 | 27 | 0 | 50 | 140 |
| 2025 | 167 | 196 | 2 | 0 | 52 | 143 |
How does Placer County compare?
How Placer County compares
Good-day share worse than typical
Placer County 45.8%
Allegheny County, Pennsylvania 46.0%
Typical US county 76.0%
Median AQI worse than typical
Placer County 52
Allegheny County, Pennsylvania 52
Typical US county 39
Unhealthy days / yr better than typical
Placer County 0
Allegheny County, Pennsylvania 0
Typical US county 1
Counties with a similar median AQI
Nationwide peers within about the same annual median AQI as Placer County (52), not geographic neighbors.
Allegheny County, Pennsylvania
Median AQI 52 · 46.0% Good-day share
Bexar County, Texas
Median AQI 52 · 43.3% Good-day share
Bibb County, Georgia
Median AQI 52 · 42.7% Good-day share
Hidalgo County, Texas
Median AQI 52 · 44.4% Good-day share
Hinds County, Mississippi
Median AQI 52 · 45.8% Good-day share
Jefferson County, Alabama
Median AQI 52 · 43.6% 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).
Weld County, Colorado
44.7% Good-day share · median AQI 52
Stanislaus County, California
49.9% Good-day share · median AQI 51
Washoe County, Nevada
50.1% Good-day share · median AQI 50
Denver County, Colorado
50.4% Good-day share · median AQI 50
Madera County, California
50.4% Good-day share · median AQI 50
Larimer County, Colorado
50.7% Good-day share · median AQI 50
California counties on the map
Geographic containment only, other monitored counties in California, independent of AQI or pollutant match.
What Placer 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 52 means for exposure. Health guidance
- See how Placer County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Placer County with its California neighbours before drawing a conclusion about the region. All of California
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 Placer County, California? ▼
Placer County has a median Air Quality Index (AQI) of 52, rated "Moderate." 45.8% of monitored days (167 out of 365) had good air quality in 2025.
What is the main pollutant in Placer County? ▼
The primary pollutant in Placer County is Ozone (O3), which was the main AQI driver on 216 days (59% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Placer County have? ▼
In 2025, Placer County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 143.
Is the air quality in Placer County getting better or worse? ▼
Air quality in Placer 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: 2024 at 51.4% (188 of 366 days). Lowest qualifying Good-day share: 2020 at 36.1% (130 of 366 days).
What does AQI 52 mean for health? ▼
Placer County's median AQI of 52 falls in the "Moderate" category. See the AQI category guide for what each range means for health.
How does Placer County compare to other counties in California? ▼
Placer County has 45.8% good air days. Nearby counties in California: Alameda (53.0% good), Amador (87.4% good), Butte (65.2% good), Calaveras (82.2% good), Colusa (79.2% good), Contra Costa (53.5% good).
What is the 90th percentile AQI in Placer County? ▼
The 90th percentile AQI for Placer County is 71, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 143 (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 Placer County, California · 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.