What was the worst air-quality day in Jacksonville?

May 17, 2007, when daily PM2.5 reached 87.9 µg/m³ (AQI 174), about 4.0 cigarette-equivalents. It ranks first of 9,184 monitored days since 1999.

What is the highest AQI recorded in Jacksonville?

On the worst day, the daily PM2.5 AQI reached 174 (Unhealthy). EPA's official metro AQI, which uses the single worst monitor of any pollutant, peaked at 174 on May 17, 2007.

Were these days caused by wildfire smoke?

This page ranks measured PM2.5 without assigning a cause: a high day can be smoke, fireworks, dust, an inversion, or industry. A separate wildfire-smoke event ranking, using a published attribution method with its version disclosed, is the next layer of this catalog.

How often does Jacksonville get air this bad?

Rarely. The record sits at the far end of 9,184 measured days; Jacksonville averages about one "unhealthy" day every 5 years.

Why did different apps show different numbers that day?

Concentration (µg/m³) and AQI are different scales; hourly, NowCast, and daily values answer different questions; a single monitor differs from a citywide composite; and live feeds get revised when EPA certifies data. This page uses the certified daily record, with the provisional tail labeled.

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Historical PM2.5 records

Jacksonville's worst air quality days

#67 of 100 US metros by worst day · Jacksonville, FL metro area

Based on the available regulatory-monitor record since 1999, May 17, 2007 ranks as Jacksonville's most severe daily PM2.5 day: 87.9 µg/m³ (AQI 174, unhealthy), about 4.0 cigarettes in a day.

Daily rank: #1
Period of record: Since 1999
Peak daily PM2.5: 87.9 µg/m³
About: 4.0 cigarettes
Latest event: 1 day, May 2026
Status: Finalized

Current conditions on the smoke map → Data through May 7, 2026 · page built July 26, 2026

Show

The worst-hit part of the metro: its highest credible monitor each day.

How this is measured sources, the daily measure, and what this ranking is not

Source. Daily PM2.5 from the U.S. EPA Air Quality System (AQS) , back to 1999, across 4 EPA monitors in the Jacksonville, FL metro area (CBSA). Days after March 31, 2026 are preliminary AirNow readings, marked provisional, and re-rank once EPA certifies them (usually the following spring).

The daily measure. "Worst area" is the metro's highest credible monitor each day, with lone bad-monitor spikes dropped (the raw single-monitor max before that filter is in the data but not charted). "Metro average" averages every monitor. The unit choice re-reads the same value as µg/m³, cigarette-equivalents (PM2.5 ÷ 22, Berkeley Earth, an illustration rather than a medical reading), or the EPA 2024 PM2.5 AQI.

Official AQI. EPA's reported metro AQI uses the single worst monitor of any pollutant, so it can run higher than the values here. The highest official daily AQI among the ranked days is 174 on May 17, 2007 (defining pollutant PM2.5).

What this ranking is not. It does not attribute days to wildfire smoke: a high-PM2.5 day can be dust, fireworks, an inversion, or industry. The wildfire-smoke event ranking below arrives with a published attribution method.

Latest major event May 2026 One ranked day, May 7, 2026, peaking at 64.9 µg/m³, #5 all-time. Provisional until EPA certifies the data. See where it ranks ↓

What were Jacksonville's worst days?

Rank	Date	Daily PM2.5
#1	May 17, 2007	87.9 µg/m³
#2	April 11, 20122-day stretch	82.8 µg/m³
#3	May 9, 2007	75.8 µg/m³
#4	April 17, 20072-day stretch	65.5 µg/m³
#5	May 7, 2026provisional	64.9 µg/m³
#6	April 18, 2007	59.2 µg/m³
#7	May 28, 20013-day stretch	55.1 µg/m³
#8	May 27, 2001	52.5 µg/m³
#9	March 4, 2000	50.8 µg/m³
#10	May 26, 2001	50.7 µg/m³
#11	May 3, 2007	48.9 µg/m³
#12	September 15, 20053-day stretch	46.8 µg/m³
#13	September 17, 2005	43 µg/m³
#14	April 10, 2012	43 µg/m³
#15	September 16, 2005	42.9 µg/m³

Days marked provisional are preliminary AirNow readings after March 31, 2026, the latest date EPA has certified for Jacksonville; they may shift once finalized.

What caused Jacksonville's worst days?

The event catalog has named 10 episodes affecting Jacksonville, each resolved to a cause only where retained evidence supports it: EPA monitor qualifiers, NWS alerts, agency statements, and reporting. The ranking above stays cause-neutral; this is where the causes live.

Wildfire smoke 2026-05-07 wildfire smoke episode affecting Jacksonville, FL May 7, 2026 · 64.9 µg/m³ here , #5 all-time · South Canal Fire
Wildfire smoke 2012-04-09 through 2012-04-11 wildfire-smoke episode affecting Jacksonville, FL Apr 11, 2012 · 82.8 µg/m³ here , #2 all-time · County Line Fire
Wildfire smoke 2007-05-17 wildfire smoke episode affecting Jacksonville, FL, Deltona-Daytona Beach-Ormond Beach, FL May 17, 2007 · 87.9 µg/m³ here , #1 all-time
Wildfire smoke 2007 Georgia-Florida wildfire-smoke transport episode May 9, 2007 · 75.8 µg/m³ here , #1 all-time · from Ware County, Georgia and northern Florida
Wildfire smoke 2007-05-03 wildfire smoke episode affecting Deltona-Daytona Beach-Ormond Beach, FL, Jacksonville, FL May 3, 2007 · 48.9 µg/m³ here , #11 all-time
Wildfire smoke 2007-04-29 wildfire smoke episode affecting Jacksonville, FL Apr 29, 2007 · 39.4 µg/m³ here , #20 all-time

4 more, plus every named episode and its evidence is in the event catalog.

How does it compare?

The record is 6% higher than the next-worst day: 87.9 µg/m³ (May 17, 2007) against 82.8 µg/m³ (April 11, 2012).

How unusual is air like this?

10× a typical day here, at the record

1 in 5 years, roughly, sees an "unhealthy" day here

0 µg/m³88 µg/m³

Every measured day near Jacksonville, by daily PM2.5; the record stands far out on the right. 30 days at "unhealthy for sensitive groups" or worse, 6 at "unhealthy", 0 at "very unhealthy" (2024 EPA thresholds, across 9,184 measured days).

Year by year (1999–2026)

Worst single day each year, by the selected measure.

Why did reported numbers differ?

During a major event, AirNow, weather apps, news reports, and neighborhood monitors can all show different figures at the same moment. All of them can be right:

Concentration vs AQI. µg/m³ is the measurement; AQI is a 0 to 500 index derived from it. "330 µg/m³" and "AQI 500" can describe the same air.
Hourly vs NowCast vs daily. An hourly peak, the NowCast rolling estimate apps display, and the full-day average answer different questions; this page ranks full days.
One monitor vs a composite. A single sensor can read far above or below a citywide figure. The measure toggle above shows both framings.
Live vs certified. Real-time feeds get corrected when EPA certifies data months later, which is why recent days here carry a provisional label.

What about indoors?

Citywide monitors can tell you what happened outside. They cannot tell you what happened inside a particular home, school, or facility: filtration, ventilation, and building operation decide that. During and after days like the ones above, outdoor particles become an indoor load question.

Check current conditions and the next clean-air window → Estimate recent filter load where you are →

Common questions

What was the worst air-quality day in Jacksonville?: May 17, 2007, when daily PM2.5 reached 87.9 µg/m³ (AQI 174), about 4.0 cigarette-equivalents. It ranks first of 9,184 monitored days since 1999.
What is the highest AQI recorded in Jacksonville?: On the worst day, the daily PM2.5 AQI reached 174 (Unhealthy). EPA's official metro AQI, which uses the single worst monitor of any pollutant, peaked at 174 on May 17, 2007.
Were these days caused by wildfire smoke?: This page ranks measured PM2.5 without assigning a cause: a high day can be smoke, fireworks, dust, an inversion, or industry. A separate wildfire-smoke event ranking, using a published attribution method with its version disclosed, is the next layer of this catalog.
How often does Jacksonville get air this bad?: Rarely. The record sits at the far end of 9,184 measured days; Jacksonville averages about one "unhealthy" day every 5 years.
Why did different apps show different numbers that day?: Concentration (µg/m³) and AQI are different scales; hourly, NowCast, and daily values answer different questions; a single monitor differs from a citywide composite; and live feeds get revised when EPA certifies data. This page uses the certified daily record, with the provisional tail labeled.

Data and citation

Ranked days for both measures are downloadable, with units and status flags: jacksonville.csv. Source: U.S. EPA Air Quality System (AQS) daily PM2.5, with preliminary AirNow readings for the uncertified tail. Cite as:

IAQng Air Records: Jacksonville, FL. iaqng.com/records/jacksonville. Data: U.S. EPA AQS and AirNow. Accessed July 26, 2026.