What was the worst air-quality day in Phoenix?

January 1, 2025, when daily PM2.5 reached 210.3 µg/m³ (AQI 285), about 9.6 cigarette-equivalents. It ranks first of 8,172 monitored days since 1999.

What is the highest AQI recorded in Phoenix?

On the worst day, the daily PM2.5 AQI reached 285 (Very unhealthy). EPA's official metro AQI, which uses the single worst monitor of any pollutant, peaked at 2403 on July 5, 2011.

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 Phoenix get air this bad?

Rarely. The record sits at the far end of 8,172 measured days; Phoenix averages 1 "unhealthy" day a year.

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

Phoenix's worst air quality days

#16 of 100 US metros by worst day · Phoenix-Mesa-Scottsdale, AZ metro area

Based on the available regulatory-monitor record since 1999, January 1, 2025 ranks as Phoenix's most severe daily PM2.5 day: 210.3 µg/m³ (AQI 285, very unhealthy), about 9.6 cigarettes in a day.

Daily rank: #1
Period of record: Since 1999
Peak daily PM2.5: 210.3 µg/m³
About: 9.6 cigarettes
Status: Finalized

Current conditions on the smoke map → Data through Mar 31, 2026 · page built July 26, 2026

Photo: Zarxos (CC BY-SA 3.0)

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 22 EPA monitors in the Phoenix-Mesa-Scottsdale, AZ 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 2403 on July 5, 2011 (defining pollutant PM10, above the scale's usual 500 cap).

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.

What were Phoenix's worst days?

Rank	Date	Daily PM2.5
#1	January 1, 2025	210.3 µg/m³
#2	January 1, 2016	152.1 µg/m³
#3	January 1, 2020	149.1 µg/m³
#4	January 1, 20182-day stretch	134.1 µg/m³
#5	January 1, 2021	131.9 µg/m³
#6	January 1, 2012	112.6 µg/m³
#7	January 1, 2024	102.8 µg/m³
#8	July 5, 2011	102.3 µg/m³
#9	January 1, 2014	101.7 µg/m³
#10	January 1, 2011	99.1 µg/m³
#11	January 1, 2013	97.3 µg/m³
#12	December 25, 2023	95.2 µg/m³
#13	December 25, 2017	86.6 µg/m³
#14	December 25, 2010	82.6 µg/m³
#15	December 31, 2017	75.6 µg/m³

What caused Phoenix's worst days?

The event catalog has named 10 episodes affecting Phoenix, 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.

Fireworks 2024-12-31 fireworks episode affecting Phoenix-Mesa-Scottsdale, AZ, Tucson, AZ Jan 1, 2025 · 210.3 µg/m³ here , #1 all-time
Mixed causes 2024-01-01 Phoenix-Mesa-Scottsdale, AZ and Tucson, AZ fireworks and winter inversion episode Jan 1, 2024 · 102.8 µg/m³ here , #7 all-time
Fireworks 2022-12-31 Tucson, AZ and Phoenix-Mesa-Scottsdale, AZ fireworks episode Jan 1, 2023 · 68.4 µg/m³ here , #19 all-time
Mixed causes 2020-12-31 2-area mixed-cause episode Jan 1, 2021 · 131.9 µg/m³ here , #5 all-time · from Phoenix-Mesa-Scottsdale, AZ
Mixed causes 2020-01-01 Phoenix-Mesa-Scottsdale mixed-cause episode Jan 1, 2020 · 149.1 µg/m³ here , #3 all-time · from Phoenix-Mesa-Scottsdale, AZ
Dust Dust episode, 2018-07-08 Jul 8, 2018 · 63.5 µg/m³ here , #21 all-time

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

How does it compare?

The record is 38% higher than the next-worst day: 210.3 µg/m³ (January 1, 2025) against 152.1 µg/m³ (January 1, 2016).

How unusual is air like this?

17× a typical day here, at the record

1 day a year, on average, at "unhealthy" or worse

2 µg/m³210 µg/m³

Every measured day near Phoenix, by daily PM2.5; the record stands far out on the right. 132 days at "unhealthy for sensitive groups" or worse, 28 at "unhealthy", 5 at "very unhealthy" (2024 EPA thresholds, across 8,172 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 Phoenix?: January 1, 2025, when daily PM2.5 reached 210.3 µg/m³ (AQI 285), about 9.6 cigarette-equivalents. It ranks first of 8,172 monitored days since 1999.
What is the highest AQI recorded in Phoenix?: On the worst day, the daily PM2.5 AQI reached 285 (Very unhealthy). EPA's official metro AQI, which uses the single worst monitor of any pollutant, peaked at 2403 on July 5, 2011.
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 Phoenix get air this bad?: Rarely. The record sits at the far end of 8,172 measured days; Phoenix averages 1 "unhealthy" day a year.
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: phoenix.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: Phoenix, AZ. iaqng.com/records/phoenix. Data: U.S. EPA AQS and AirNow. Accessed July 26, 2026.