What was the worst air-quality day in Las Vegas?

August 7, 2021, when daily PM2.5 reached 100.7 µg/m³ (AQI 183), about 4.6 cigarette-equivalents. It ranks first of 8,744 monitored days since 1999.

What is the highest AQI recorded in Las Vegas?

On the worst day, the daily PM2.5 AQI reached 183 (Unhealthy). EPA's official metro AQI, which uses the single worst monitor of any pollutant, peaked at 480 on September 8, 2022.

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 Las Vegas get air this bad?

Rarely. The record sits at the far end of 8,744 measured days; Las Vegas averages about one "unhealthy" day every 3 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

Las Vegas's worst air quality days

#56 of 100 US metros by worst day · Las Vegas-Henderson-Paradise, NV metro area

Based on the available regulatory-monitor record since 1999, August 7, 2021 ranks as Las Vegas's most severe daily PM2.5 day: 100.7 µg/m³ (AQI 183, unhealthy), about 4.6 cigarettes in a day.

Daily rank: #1
Period of record: Since 1999
Peak daily PM2.5: 100.7 µg/m³
About: 4.6 cigarettes
Status: Finalized

Current conditions on the smoke map → Data through Apr 30, 2026 · page built July 26, 2026

Photo: Antoine Taveneaux (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 19 EPA monitors in the Las Vegas-Henderson-Paradise, NV metro area (CBSA). Days after April 30, 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 480 on September 8, 2022 (defining pollutant PM10).

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 Las Vegas's worst days?

Rank	Date	Daily PM2.5
#1	August 7, 2021	100.7 µg/m³
#2	July 4, 2003	84.6 µg/m³
#3	September 11, 2024	83.3 µg/m³
#4	July 30, 2016	69.9 µg/m³
#5	January 1, 2014	68.2 µg/m³
#6	January 1, 2012	61.2 µg/m³
#7	September 8, 20222-day stretch	59.5 µg/m³
#8	August 19, 2021	59.3 µg/m³
#9	December 26, 2001	56.1 µg/m³
#10	September 7, 2020	49.8 µg/m³
#11	September 9, 2022	49.8 µg/m³
#12	August 5, 2018	49.6 µg/m³
#13	January 1, 2009	49.3 µg/m³
#14	July 4, 2006	48.5 µg/m³
#15	January 1, 2001	47.1 µg/m³

What caused Las Vegas's worst days?

The event catalog has named 15 episodes affecting Las Vegas, 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 September 9–11, 2024 Southern California wildfire-smoke episode Sep 11, 2024 · 83.3 µg/m³ here , #3 all-time · from Southern California
Fireworks 2024-07-04 Las Vegas-Henderson-Paradise, NV fireworks episode Jul 4, 2024 · 43.9 µg/m³ here , #18 all-time
Wildfire smoke 2024-06-16 Las Vegas-Henderson-Paradise, NV wildfire smoke episode Jun 16, 2024 · 39 µg/m³ here , #25 all-time · from Arizona
Dust 2022-09-08 Las Vegas-Henderson-Paradise, NV dust episode Sep 8, 2022 · 59.5 µg/m³ here , #7 all-time
Dust 2022-04-11 Las Vegas-Henderson-Paradise, NV dust episode Apr 11, 2022 · 40.8 µg/m³ here , #22 all-time
Wildfire smoke 2021-08-19 Las Vegas-Henderson-Paradise wildfire-smoke episode Aug 19, 2021 · 59.3 µg/m³ here , #8 all-time · from Las Vegas-Henderson-Paradise, NV

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

How does it compare?

The record is 19% higher than the next-worst day: 100.7 µg/m³ (August 7, 2021) against 84.6 µg/m³ (July 4, 2003).

How unusual is air like this?

11× a typical day here, at the record

1 in 3 years, roughly, sees an "unhealthy" day here

0 µg/m³101 µg/m³

Every measured day near Las Vegas, by daily PM2.5; the record stands far out on the right. 43 days at "unhealthy for sensitive groups" or worse, 9 at "unhealthy", 0 at "very unhealthy" (2024 EPA thresholds, across 8,744 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 Las Vegas?: August 7, 2021, when daily PM2.5 reached 100.7 µg/m³ (AQI 183), about 4.6 cigarette-equivalents. It ranks first of 8,744 monitored days since 1999.
What is the highest AQI recorded in Las Vegas?: On the worst day, the daily PM2.5 AQI reached 183 (Unhealthy). EPA's official metro AQI, which uses the single worst monitor of any pollutant, peaked at 480 on September 8, 2022.
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 Las Vegas get air this bad?: Rarely. The record sits at the far end of 8,744 measured days; Las Vegas averages about one "unhealthy" day every 3 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: las-vegas.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: Las Vegas, NV. iaqng.com/records/las-vegas. Data: U.S. EPA AQS and AirNow. Accessed July 26, 2026.