2018-02-22 Denver-Aurora-Lakewood, CO temperature-inversion pollution episode
February 22, 2018
Daily PM2.5 peaked at 46.6 µg/m³ near Denver across
1 covered metro home to 3.1 million people.
Counting the extra PM2.5 above each metro's typical day, this event handed the
average affected resident ≈ 1.7 cigarettes.
Across everyone living in the affected metros, that is the collective equivalent of
≈ 5.3 million cigarettes.
An awareness illustration of outdoor exposure at 22 µg/m³
per cigarette (Berkeley Earth), counting only the event's ranked days; not a
medical dose.
Why we think this happened
The basis for “Temperature inversion”
Denver's public-health department retrospectively identifies February 22, 2018 as an elevated-pollution day caused by an all-day inversion that surface heating could not erode. EPA monitors independently establish the same-day PM2.5 episode. This supports temperature inversion at possible confidence while leaving the contributing emission sectors unallocated.
PossibleThis is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
Denver Department of Public Health and Environment · Jul 17, 2018official
Denver's public-health department identified February 22 as an elevated-pollution day under an all-day inversion. Its presentation says the greatest impacts extended through the South Platte River valley from Boulder and Chatfield to Greeley; increasing cloud and late light snow prevented surface heating from eroding the inversion, and a visibility camera showed aerosols obscuring the mountains.
EPA records show a median daily PM2.5 value of 31.9542 micrograms per cubic meter across 7 Denver-area monitors on February 22, compared with 9.9 before and 10.0604 after the event.
Inference, not direct attribution
official_retrospective_inversion_assessment_possible.v1: This inference is recorded in the catalog methodology.
A cause is more convincing when the record connects three things: something happened,
the air mass moved toward the region, and local instruments responded. Here is how much
of that chain is documented for this event.
Denver's public-health department identified February 22 as an elevated-pollution day under an all-day inversion. Its presentation says the greatest impacts extended through the South Platte River valley from Boulder and Chatfield to Greeley;…
The retained record does not yet show how air traveled from the proposed source to
these metros. A trajectory replay or dated plume analysis belongs here.
Research gap
3
Local response
46.6 µg/m³ near Denver
EPA monitors recorded the event across 1 metro.
The peak daily concentration is roughly 2.1 cigarette-equivalents at the outdoor daily rate.
Before, during, and after the episode: nearby pollutant monitors and surface-weather
stations show what changed. This context tests the “Temperature inversion” explanation; it does
not assign the cause by itself.
Observed context · not attribution
Denver-Aurora-Lakewood, CO
Monitor comparison window 2018-02-19 to 2018-02-25 · PM2.5 target: Chatfield State Park
6 pollutant signals
Fine-particle pulse32 µg/m³
218% above nearby days
Air movement4 kt median wind
8 calm hours observed
What observers saw0.5 mi minimum visibility
5 hours at or below 3 miles
Pollution fingerprint
Metro-wide median of reporting monitors
PM2.532 µg/m³
218% higher than surrounding days
Before9.90 µg/m³ Event32 µg/m³ After10.1 µg/m³
PM1040.5 µg/m³
125% higher than surrounding days
Before38 µg/m³ Event40.5 µg/m³ After15.5 µg/m³
Carbon monoxide0.576 ppm
67% higher than surrounding days
Before0.344 ppm Event0.576 ppm After0.343 ppm
Nitrogen dioxide41.9 ppb
59% higher than surrounding days
Before26.3 ppb Event41.9 ppb After20.6 ppb
Sulfur dioxide1 ppb
97% higher than surrounding days
Before0.508 ppb Event1 ppb After0.392 ppb
Ozone0.029 ppm
About the same as surrounding days
Before0.022 ppm Event0.029 ppm After0.043 ppm
Atmospheric conditions
DENVER/CENTENNIAL, 19.3 km from the PM2.5 target
Wind4 kt median
9 kt maximum · 8 of 24 observed hours calm
Visibility0.5 mi minimum
5 observed hours at or below 3 miles
Temperature20.45°F median
10.9°F to 28°F
Humidity84% median
95% maximum
Source: U.S. EPA AirData daily observations and, where available, nearby ASOS/AWOS
surface observations. Values are descriptive medians over the retained monitor set;
missing measurements remain missing. Transport and source evidence remain separate
layers because this instrument pattern does not assign a cause by itself.
Measured daily PM2.5 at EPA monitors, as cigarette-equivalents
EPA monitors sit in metro areas, so the colour clusters there. Land between and beyond
them is unmeasured, not clean: this map shows where IAQng has readings, not the extent
of the smoke.
—
Episode peak
--cigarettes
The smoke map's scale, replayed over this event: the surface interpolates between
covered metros' daily records, framed to the affected region. Hover for a reading,
click a metro to pin it to the card. Days a monitor did not report draw nothing.
Select a metro on the map to see nearby cameras. Where an operator archive reaches
the event, drag the divider to compare two moments, adjust either date and time, or
play the available event-day frames. Camera imagery is visual context, not an
air-quality measurement or proof of smoke.
No useful public camera views are currently available within 80 km of this metro.
"Cigarettes, whole event" totals a metro's ranked event days at 22 µg/m³ per
cigarette: what a person outdoors there breathed across the event, as the
illustration. "All-time standing" is where this episode's days sit in each metro's
ranked record (worst-area measure, since 1999). Full local context is on each
metro's Air Records page.
Public evidence library
What supports this account
Each card states what a source supports—and what it does not. Official records, research, reporting, community observations, and transparent inferences remain visibly different kinds of evidence.
3 retained sources
Official record
Air Monitoring in North Denver: February 22, 2018 elevated-pollution-day analysis
Denver Department of Public Health and Environment
Denver's public-health department identified February 22 as an elevated-pollution day under an all-day inversion. Its presentation says the greatest impacts extended through the South Platte River valley from Boulder and Chatfield to Greeley; increasing cloud and late light snow prevented surface heating from eroding the inversion, and a visibility camera showed aerosols obscuring the mountains.
What it supports
An official source supports the attributed cause for the stated place and dates.
Limit
The original Denver-hosted presentation was not recovered; the retained public copy is a full-text third-party mirror of the government-authored slides.
Official record
Denver modeled aerosol fingerprint, February 22, 2018
U.S. EPA EQUATES CMAQ via Remote Sensing Information Gateway
EPA's retrospective model reproduced an event-day fine-mass increase of 3.2167 times adjacent modeled days. Secondary ions represented 52.5 percent and organic matter 35.8 percent of modeled fine mass.
What it supports
Context for the event; this item does not establish the attributed cause by itself.
Limit
EQUATES is modeled composition context, not a monitor observation or source-apportionment determination.
Official record
Denver measured PM2.5 fingerprint, February 22, 2018
U.S. EPA AirData
EPA records show a median daily PM2.5 value of 31.9542 micrograms per cubic meter across 7 Denver-area monitors on February 22, compared with 9.9 before and 10.0604 after the event.
What it supports
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
Limit
The monitor record establishes the particle episode but cannot identify its mechanism by itself.
What remains uncertain
EQUATES is modeled composition context, not a monitor observation or source-apportionment determination.
The assessment identifies the trapping mechanism but does not apportion mobile, residential, industrial, or other source-sector shares.
The classification identifies atmospheric trapping, not a complete emissions inventory for the day.
The monitor record establishes the particle episode but cannot identify its mechanism by itself.
The original Denver-hosted presentation was not recovered; the retained public copy is a full-text third-party mirror of the government-authored slides.
Status and provenance
PossibleThis is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
This episode was grouped from the monitor record by the catalog pipeline and given
its cause from the evidence listed above. It has not been individually reviewed and
signed off, so its boundaries, cause, and name may change as evidence accumulates.
Grouping policy common_sense_root_cause_grouping.v2. The cause label reflects the
assembled evidence above, not an IAQng detection formula. If it is wrong,
tell us.