Peer-reviewed study corroborates
Wintertime PM2.5 during persistent multi-day cold-air pools
The study documents persistent winter 2009-2010 cold-air pools and PM2.5 accumulation in northern Utah.
Temperature inversion Likely
2010-01-11 to 2010-01-13 Ogden-Clearfield, UT and Salt Lake City, UT temperature-inversion pollution episode
Daily PM2.5 peaked at 76.7 µg/m³ near Salt Lake City across 2 covered metros home to 2.0 million people.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 6.6 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 13 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”
Peer-reviewed Utah cold-air-pool research covers the winter 2009-2010 period and documents persistent inversion-driven PM2.5 buildup.
Likely Applicable reporting or a supported inference makes this the best current causal explanation.
See every retained source and limitation ↓
Sequence: Salt Lake City (Jan 11) → Ogden (Jan 11)
Evidence path
From source to city
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.
- 1Documented
Source or mechanism
Temperature inversion
The study documents persistent winter 2009-2010 cold-air pools and PM2.5 accumulation in northern Utah.
View supporting source ↗ - 2Research gap
Air-mass movement
The transport path has not been reconstructed
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.
- 3Documented
Local response
76.7 µg/m³ near Salt Lake City
EPA monitors recorded the event across 2 metros. The peak daily concentration is roughly 3.5 cigarette-equivalents at the outdoor daily rate.
Inspect the pollutant and weather signals ↓
Event autopsy
What the instruments saw
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.
Ogden-Clearfield, UT
Monitor comparison window 2010-01-08 to 2010-01-16 · PM2.5 target: Bountiful Viewmont
29% above nearby days
7% higher than surrounding days
47% higher than surrounding days
Pollution fingerprint
Metro-wide median of reporting monitors PM2.5 55 µg/m³
29% higher than surrounding days
Before35.4 µg/m³ Event55 µg/m³ After35.6 µg/m³
PM10 75 µg/m³
47% higher than surrounding days
Before51 µg/m³ Event75 µg/m³ After45 µg/m³
Carbon monoxide 1.39 ppm
21% higher than surrounding days
Before1.15 ppm Event1.39 ppm After0.846 ppm
Nitrogen dioxide 43.3 ppb
13% higher than surrounding days
Before38.4 ppb Event43.3 ppb After31.4 ppb
Sulfur dioxide 3.57 ppb
7% higher than surrounding days
Before3.43 ppb Event3.57 ppb After2.04 ppb
Ozone 0.006 ppm
About the same as surrounding days
Before0.007 ppm Event0.006 ppm After0.005 ppm
Atmospheric conditions
Nearby EPA weather observationsAbout the same as surrounding days
About the same as surrounding days
About the same as surrounding days
7% higher than surrounding days
Salt Lake City, UT
Monitor comparison window 2010-01-08 to 2010-01-16 · PM2.5 target: Hawthorne
38% above nearby days
46% higher than surrounding days
Pollution fingerprint
Metro-wide median of reporting monitors PM2.5 67.8 µg/m³
38% higher than surrounding days
Before49.3 µg/m³ Event67.8 µg/m³ After30 µg/m³
PM10 104 µg/m³
46% higher than surrounding days
Before71 µg/m³ Event104 µg/m³ After48 µg/m³
Carbon monoxide 1.51 ppm
84% higher than surrounding days
Before1 ppm Event1.51 ppm After0.692 ppm
Nitrogen dioxide 49.5 ppb
16% higher than surrounding days
Before43.4 ppb Event49.5 ppb After33.3 ppb
Sulfur dioxide 2.54 ppb
17% higher than surrounding days
Before2.08 ppb Event2.54 ppb After2.04 ppb
Ozone 0.006 ppm
About the same as surrounding days
Before0.007 ppm Event0.006 ppm After0.005 ppm
Atmospheric conditions
Nearby EPA weather observationsAbout the same as surrounding days
About the same as 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.
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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.
Views from the selected metro
Camera views near
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.
Affected metros
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| Salt Lake City, UT | 76.7 µg/m³ | 10.0 | Jan 12, 2010 | #15 of its top days |
| Ogden-Clearfield, UT | 57 µg/m³ | 2.6 | Jan 11, 2010 | #22 of its top days |
"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.
Wintertime PM2.5 during persistent multi-day cold-air pools
Peer-reviewed study
The study documents persistent winter 2009-2010 cold-air pools and PM2.5 accumulation in northern Utah.
What it supports
A retained source supports the attributed cause for the stated place and dates.
Limit
The accessible snippet does not provide a day-by-day January 11-13 table.
What remains uncertain
- The classification is bounded to the retained evidence and does not apportion every source contributing to the daily PM2.5 value.
Status and provenance
Likely Applicable 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.