63% above nearby days
Temperature inversion Possible
2011-01-15 Ogden-Clearfield, UT temperature-inversion pollution episode
Daily PM2.5 peaked at 56.6 µg/m³ near Ogden across 1 covered metro home to 667,681 people.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 2.2 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 1.5 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”
The date falls within Utah's winter cold-pool regime and official historical data preserve the high observation; no exact narrative was recovered.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
Inference, not direct attribution
Winter inversion pattern: The place and date match a known winter-inversion regime. This is a pattern-based hypothesis without an exact event attribution.
Standard review is complete, but no retained public source directly attributes this event. Any displayed cause therefore rests on the catalog’s documented inference or grouping logic and remains unconfirmed.
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.
- 1Inferred
Source or mechanism
Pattern-based explanation
Winter inversion pattern. The place and date match a known winter-inversion regime. This is a pattern-based hypothesis without an exact event attribution.
- 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
56.6 µg/m³ near Ogden
EPA monitors recorded the event across 1 metro. The peak daily concentration is roughly 2.6 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 2011-01-12 to 2011-01-18 · PM2.5 target: Ogden
10% higher than surrounding days
31% higher than surrounding days
Pollution fingerprint
Metro-wide median of reporting monitors PM2.5 56 µg/m³
63% higher than surrounding days
Before44.6 µg/m³ Event56 µg/m³ After3.65 µg/m³
PM10 57.5 µg/m³
31% higher than surrounding days
Before56 µg/m³ Event57.5 µg/m³ After23 µg/m³
Carbon monoxide 0.969 ppm
31% higher than surrounding days
Before0.739 ppm Event0.969 ppm After0.649 ppm
Nitrogen dioxide 32 ppb
About the same as surrounding days
Before34.5 ppb Event32 ppb After20.9 ppb
Sulfur dioxide 2.08 ppb
43% higher than surrounding days
Before1.50 ppb Event2.08 ppb After0.958 ppb
Ozone 0.015 ppm
17% lower than surrounding days
Before0.015 ppm Event0.015 ppm After0.029 ppm
Atmospheric conditions
Nearby EPA weather observations10% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
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.
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 |
|---|---|---|---|---|
| Ogden-Clearfield, UT | 56.6 µg/m³ | 2.6 | Jan 15, 2011 | #23 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.
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
Possible This 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.