California · County air quality · 2024
Alameda County, California
Median AQI 49 (Good). 53.0% of monitored days rated Good, direct from EPA Air Quality System stations.
- 49
- Median AQI
- 53.0%
- Good-air days
- 0
- Unhealthy days
- 0%
- Cleaner than US counties
Alameda County's 2024 annual median AQI is 49 (Good), with 53.0% Good days
According to the U.S. EPA Air Quality System, Alameda County, California posted a 2024 median AQI of 49 (Good) across 366 monitored days, with 53.0% 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
- Alameda County's 53.0% Good-day share places it cleaner than 0% of US counties in 2024.
- Closest median-AQI peer
- Contra Costa County (53.5% Good, median AQI 48) is the closest nationwide median-AQI peer to Alameda County.
- 2020–2024 trend
- Alameda County's floor-qualifying Good-day share is improving from 2020 to 2024 (46.3% → 53.0%).
- Median AQI
- Median AQI: 49
According to the 2024 EPA AQS county release on PlainAirData, Alameda County, California ranks #15 of 15 by median AQI (49) and #15 by good-day share (53.0%). San Mateo County, California is #1 of 15 by median AQI (27, 88.1% Good days) at good-day-share #5 ≠ Chattooga County, Georgia #1 by good-day share (96.3%, median AQI 39) at median-AQI #5.
Annual release change
What changed in the 2024 EPA annual release
- Alameda County's peak single-day AQI fell from 130 to 105 between the 2023 and 2024 EPA annual releases, a change of -25 points.
Data updated August 2026
- Good · 194 d · 53.0%
- Moderate · 171 d · 46.7%
- USG · 1 d · 0.3%
How did Alameda County's air break down in 2024?
Across 366 monitored days, 194 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 →Share of monitored days at AQI 0-50 (Good band).
Share of monitored days above AQI 150 (Unhealthy or worse). Bar maxes at 10% (worst-county ceiling).
Where Alameda County sits nationally
COUNT-derived placement among 951 US counties with at least 100 monitored days in 2024. Alameda County's Good-day share is 53.0% - cleaner than 0% of that comparison set.
Alameda County Good-day share vs. every US county
Share of monitored days in the Good band (AQI 0–50) - EPA AQS annual release
53.0% 0th percentile higher than 0% of 951 US counties
Each bar is a band; taller bars hold more US counties. The dashed line + filled bar mark this entry. Hover or tap any bar for its full count, share, and where it sits relative to this entry.
Source U.S. Environmental Protection Agency, Air Quality System (AQS) · 2024
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Alameda County.
- PM2.5 · 352 days · 96.2%
- Ozone · 14 days · 3.8%
2024 daily-monitor rhythm in Alameda County
Month-by-month median AQI from EPA day-level county monitors (366 reported days in 2024). Dec posted the highest typical readings (median AQI 57, peak 105); Mar was cleanest at median 34. Summer months (Jun–Aug) averaged median AQI 53 vs 47 in Dec–Feb.
Five-year seasonal record
EPA day-level county files · 2020–20241,827 daily readings show a recurring local pattern: Sep has the highest matched-month median AQI (57), while Mar is lowest (41). Each cell is that month’s median daily AQI, not a current-air forecast.
Lower AQI is better. The colors summarize EPA AQI bands; gaps mean the county had no day-level record for that month.
Health Impact Assessment
Alameda County's air quality is rated Moderate based on 53.0% good air days. No unhealthy air days were recorded in 2024.
Air quality was acceptable on 53.0% of monitored days in 2024, with a median AQI of 49. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is PM2.5, driving AQI on 352 of 366 monitored days.
5-Year Air Quality Trend
Air quality is improving in Alameda County. Highest Good-day share: 2023 (54.0%, 197 of 365 monitored days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 169 | 177 | 8 | 11 | 52 | 243 |
| 2021 | 155 | 200 | 9 | 1 | 53 | 151 |
| 2022 | 185 | 175 | 5 | 0 | 49 | 122 |
| 2023 | 197 | 155 | 13 | 0 | 48 | 130 |
| 2024 | 194 | 171 | 1 | 0 | 49 | 105 |
How does Alameda County compare?
How Alameda County compares
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 Alameda County, California · 2020–2025
Download this county's annual AQI row as CSV , with the same EPA fields and denominator shown on this page.
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.