2017-02-01 to 2017-02-02 Ogden-Clearfield, UT and Provo-Orem, UT temperature-inversion pollution episode
February 1, 2017 to February 2, 2017
Daily PM2.5 peaked at 75.3 µg/m³ near Provo across
2 covered metros home to 1.4 million people.
Counting the extra PM2.5 above each metro's typical day, this event handed the
average affected resident ≈ 2.8 cigarettes.
Across everyone living in the affected metros, that is the collective equivalent of
≈ 3.9 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”
Exact-date meteorological observations and peer-reviewed sampling identify a deep valley cold pool capped by a strong inversion with unhealthy PM2.5.
LikelyApplicable reporting or a supported inference makes this the best current causal explanation.
Utah Department of Environmental Quality, Division of Air Quality · Mar 16, 2018official
The UDAQ-hosted technical report identifies January 27 through February 4, 2017 as a northern Utah pollution episode and assesses persistent cold-air-pool meteorology, trapped emissions, and secondary ammonium-nitrate formation during the episode. Its measurements and analysis explicitly include Utah Valley sites at North Provo and Lindon, supporting winter inversion and associated secondary-particle formation for the Provo-Orem portion of the supplied February 1 event. It does not directly assess the supplied Ogden-Clearfield portion.
University of Utah / Wasatch Weather Weenies · Feb 1, 2017corroborates
A University of Utah meteorologist documented a deep valley cold pool capped by a strong inversion and unhealthy PM2.5 across the Great Salt Lake and Utah Lake valleys during the event.
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.
A University of Utah meteorologist documented a deep valley cold pool capped by a strong inversion and unhealthy PM2.5 across the Great Salt Lake and Utah Lake valleys during the event.
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
75.3 µg/m³ near Provo
EPA monitors recorded the event across 2 metros.
The peak daily concentration is roughly 3.4 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.
Monitor comparison window 2017-01-29 to 2017-02-05 · PM2.5 target: Brigham City
5 pollutant signals
Fine-particle pulse51.8 µg/m³
40% above nearby days
Air movement286 Degrees Compass
10% higher than surrounding days
PM1071 µg/m³
46% higher than surrounding days
Pollution fingerprint
Metro-wide median of reporting monitors
PM2.551.8 µg/m³
40% higher than surrounding days
Before36 µg/m³ Event51.8 µg/m³ After6.90 µg/m³
PM1071 µg/m³
46% higher than surrounding days
Before46 µg/m³ Event71 µg/m³ After18 µg/m³
Carbon monoxide0.844 ppm
33% higher than surrounding days
Before0.517 ppm Event0.844 ppm After0.792 ppm
Nitrogen dioxide36.2 ppb
23% higher than surrounding days
Before30 ppb Event36.2 ppb After26.9 ppb
Ozone0.008 ppm
62% lower than surrounding days
Before0.021 ppm Event0.008 ppm After0.022 ppm
Atmospheric conditions
Nearby EPA weather observations
Humidity82.8 %
About the same as surrounding days
Pressure866 Millibars
About the same as surrounding days
Temperature28.8 °F
About the same as surrounding days
Wind286 Degrees Compass
10% higher than surrounding days
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.
1 retained source
Official record
A Thinning Cold Pool
University of Utah / Wasatch Weather Weenies
A University of Utah meteorologist documented a deep valley cold pool capped by a strong inversion and unhealthy PM2.5 across the Great Salt Lake and Utah Lake valleys during the event.
What it supports
A retained source supports the attributed cause for the stated place and dates.
Limit
The source explains accumulation but not the emission-source mixture.
What remains uncertain
Mechanism classification only.
Status and provenance
LikelyApplicable reporting or a supported inference makes this the best current causal explanation.
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.