State air quality · 2025

Louisiana Air Quality Ranking

Across 22 monitored counties, the typical county in Louisiana posts a median AQI of 41 (Good) and 74.6% of monitored days were rated Good, from EPA AQS.

41
Avg median AQI
74.6%
Good-air days
22
Counties monitored
37%
Cleaner than US states

Louisiana's typical county median AQI is 41 (Good) across 22 monitored counties

According to the U.S. EPA Air Quality System, Louisiana monitors 22 counties with a day-weighted Good-day share of 74.6%. Cleanest: Ascension County (95.6% Good). Most polluted: West Baton Rouge County (49.3%). These are annual summaries, not live AirNow readings.

Data source EPA Air Quality System (AQS)

Cleaner than US states
Louisiana's day-weighted Good-day share of 74.6% places it cleaner than 37% of US states.
In-state spread
Within Louisiana, Ascension County leads at 95.6% Good days while West Baton Rouge County sits at 49.3% across 22 monitored counties.
2024→2025 release
Louisiana's Good-day share moved +4.4 points vs the 2024 EPA annual release.
Typical median AQI
Typical median AQI: 41

Verify with AirNow → · EPA AQS →

EPA state monitoring brief

AQS state key LOUISIANA

Louisiana · 2025 EPA AQS · 22 counties · med AQI 41 · 74.6% Good · Ascension→West Baton Rouge spread

  • GOOD 41 Median AQI · Good
  • SHARE 74.6% Good-day share
  • COUNT 22 Counties monitored
  • UNH 0 Unhealthy+ days
  • RANK 37% Cleaner than states
  • O3 57.1% Main pollutant share

Good-day share peers

Kansas74.7%Michigan74.7%Louisiana (this)74.6%Delaware74.1%
Good-day share neighbourhood · nearest ABS peers vs Louisiana

Louisiana's 74.6% Good-day share is cleaner than 37% of monitored US states; Ascension and West Baton Rouge County bracket the in-state range. Open Ascension County →

According to EPA AQS annual summaries on PlainAirData, Louisiana ranks #33 of 52 by day-weighted good-day share (74.6%) and #38 by mean county median AQI (41.3). Hawaii is #1 of 52 by day-weighted good-day share (93.8% of monitored days) at mean county median-AQI #4 (27.3) ≠ Alaska #1 lowest mean county median AQI (20.3) at good-day share #8 (84.4%).

Data updated August 2026

What changed, what drives it, and how thick is the sample

Three derived views WPR-style word count does not substitute for: release-over-release movement from county annual rows, the EPA main-pollutant day mix, and how many counties sit below the 100-day ranking floor.

Release change

74.6%

Good-day share in 2025, up 4.4 percentage points vs 2024. County-mean median AQI 41, 1.1 points lower (cleaner) than 2024.

Pollutant mix

Ozone

Main driver on 57.1% of pollutant-assigned days.

  • Ozone 57.1%
  • PM2.5 42.3%
  • NO2 0.5%
  • PM10 0.1%

Monitoring coverage

331

Average monitored days per county in the latest release. Every monitored county clears the 100-day ranking floor.

Counties Monitored

22

Good Days %

74.6%

Avg Median AQI

41

Total Unhealthy Days

0

Best Air Quality

Ascension County

Worst Air Quality

West Baton Rouge County

Where Louisiana sits nationally

COUNT-derived placement among 52 US states with at least 365 monitored days in the latest county release. Louisiana's day-weighted Good-day share is 74.6% - cleaner than 37% of that comparison set.

Louisiana Good-day share vs. every US state

Day-weighted share of monitored days in the Good band (AQI 0–50) - EPA AQS annual release

74.6% 37th percentile higher than 37% of 52 US states

0.0%–5.0%: 0 US states (0%). Below this entry. 5.0%–10.0%: 0 US states (0%). Below this entry. 10.0%–15.0%: 0 US states (0%). Below this entry. 15.0%–20.0%: 0 US states (0%). Below this entry. 20.0%–25.0%: 0 US states (0%). Below this entry. 25.0%–30.0%: 0 US states (0%). Below this entry. 30.0%–35.0%: 0 US states (0%). Below this entry. 35.0%–40.0%: 0 US states (0%). Below this entry. 40.0%–45.0%: 0 US states (0%). Below this entry. 45.0%–50.0%: 0 US states (0%). Below this entry. 50.0%–55.0%: 0 US states (0%). Below this entry. 55.0%–60.0%: 0 US states (0%). Below this entry. 60.0%–65.0%: 2 US states (4%). Below this entry. 65.0%–70.0%: 9 US states (17%). Below this entry. 70.0%–75.0%: 11 US states (21%). This entry sits in this band. 75.0%–80.0%: 11 US states (21%). Above this entry. 80.0%–85.0%: 13 US states (25%). Above this entry. 85.0%–90.0%: 5 US states (10%). Above this entry. 90.0%–95.0%: 1 US states (2%). Above this entry. 95.0%–100.0%: 0 US states (0%). Above this entry. 100.0%–105.0%: 0 US states (0%). Above this entry. This state 0.0% 100% every floor-qualified US state, bucketed by value

Each bar is a band; taller bars hold more US states. 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) · 2025

Which counties in Louisiana have the cleanest and most polluted air?

Cleanest counties in Louisiana

Share of monitored days rated Good (AQI 0–50)

  1. 1 Ascension County 95.6%
  2. 2 St. James County 93.9%
  3. 3 Pointe Coupee County 93.7%
  4. 4 St. John the Baptist County 93.1%
  5. 5 St. Martin County 92.2%
  6. 6 St. Tammany County 86.8%
  7. 7 Caddo County 80%
  8. 8 Tangipahoa County 79.5%
  9. 9 Bossier County 78.9%
  10. 10 Iberville County 78.6%
  11. 11 Rapides County 73.7%
  12. 12 Terrebonne County 73%

Good-day share · EPA Air Quality System

County Good % Median AQI
Ascension 95.6% 33
St. James 93.9% 33
Pointe Coupee 93.7% 35
St. John the Baptist 93.1% 34
St. Martin 92.2% 36
St. Tammany 86.8% 37
Caddo 80.0% 38
Tangipahoa 79.5% 41
Bossier 78.9% 42
Iberville 78.6% 40
Rapides 73.7% 37
Terrebonne 73.0% 42
St. Bernard 72.9% 44
Orleans 71.0% 42
Lafourche 67.4% 44
Lafayette 65.8% 45
Calcasieu 62.2% 47
Jefferson 62.2% 47
Ouachita 62.2% 45
Livingston 62.0% 45
East Baton Rouge 49.6% 51
West Baton Rouge 49.3% 51

Data Sources

Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by County dataset, 2020–2025. See our methodology for how AQI and median figures are computed.

Coverage: 22 counties in Louisiana with active monitoring stations. Unmonitored counties are not represented.

Source: U.S. EPA Air Quality System (AQS) Annual AQI by county summary files, aggregated to the state level · 2020–2025

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.

Informational only, not professional advice. Data from EPA AQS. See our disclaimer.