Winter inversion Corroborated
Daily PM2.5 peaked at 100.2 µg/m³ near Ogden across 2 covered metros home to 2.0 million people. 1 metro recorded their worst day on record; 2 placed a top-ten day.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 6.2 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 12 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
Qualified frozen evidence supports winter inversion as the broad root cause.
Corroborated Independent reporting agrees on the cause, with no agency determination, monitor flag, or published assessment behind it.
Deseret News · Feb 6, 2002 corroborates
Contemporaneous reporting says a warm-air lid was trapping cold air and pollution across the Wasatch Front; Utah air officials imposed red no-burn days in Salt Lake and Davis counties and a yellow day in Weber County during the event window.
Journal of the Air & Waste Management Association · Dec 1, 2005 corroborates
The study's 2002 Winter Olympic monitoring discussion identifies February 7 as a time of strong inversion, corroborating an inversion condition during this Salt Lake City–Ogden event; it does not apportion emissions sources.
See every retained source and limitation ↓
Sequence: Salt Lake City (Feb 6) → Ogden (Feb 7)
Evidence path
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.
Source or mechanism
Contemporaneous reporting says a warm-air lid was trapping cold air and pollution across the Wasatch Front; Utah air officials imposed red no-burn days in Salt Lake and Davis counties and a yellow day in Weber County during the event window.
View supporting source ↗Air-mass movement
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.
Local response
The study's 2002 Winter Olympic monitoring discussion identifies February 7 as a time of strong inversion, corroborating an inversion condition during this Salt Lake City–Ogden event; it does not apportion emissions sources.
Inspect the pollutant and weather signals ↓Event autopsy
Before, during, and after the episode: nearby pollutant monitors and surface-weather stations show what changed. This context tests the “Winter inversion” explanation; it does not assign the cause by itself.
Salt Lake City, UT
Monitor comparison window 2002-02-03 to 2002-02-10 · PM2.5 target: UTM COORDINATES = INLET PROBE LOCATION ON ROOF OF TRAILER
48% above nearby days
54% higher than surrounding days
48% higher than surrounding days
54% higher than surrounding days
14% higher than surrounding days
28% higher than surrounding days
29% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
Ogden-Clearfield, UT
Monitor comparison window 2002-02-03 to 2002-02-10 · PM2.5 target: Ogden
48% above nearby days
73% higher than surrounding days
48% higher than surrounding days
73% higher than surrounding days
31% higher than surrounding days
30% higher than surrounding days
51% higher than 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.
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
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.
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| Ogden-Clearfield, UT | 100.2 µg/m³ | 4.6 | Feb 7, 2002 | Worst day on record |
| Salt Lake City, UT | 91.6 µg/m³ | 8.0 | Feb 7, 2002 | #2 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
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.
Deseret News
Contemporaneous reporting says a warm-air lid was trapping cold air and pollution across the Wasatch Front; Utah air officials imposed red no-burn days in Salt Lake and Davis counties and a yellow day in Weber County during the event window.
A retained source supports the event interpretation for the stated place and dates.
The article identifies the accumulation mechanism but does not apportion the trapped particulate mass among individual emissions sources.
Corroborated Independent reporting agrees on the cause, with no agency determination, monitor flag, or published assessment behind it.
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.