Brigham Young University corroborates
The Daily Universe, January 20, 2004
Contemporaneous reporting explains that an inversion was trapping PM2.5 across northern Utah during the exact event window.
Temperature inversion Likely
2004-01-19 to 2004-01-20 Ogden-Clearfield, UT and Provo-Orem, UT temperature-inversion pollution episode
Daily PM2.5 peaked at 77.5 µg/m³ near Provo across 2 covered metros home to 1.4 million people. 1 metro placed a top-ten day in their record.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 3.1 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 4.4 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”
Contemporaneous Utah reporting and scientific analysis identify a persistent January 2004 inversion and extreme fine-particle buildup.
Likely Applicable reporting or a supported inference makes this the best current causal explanation.
See every retained source and limitation ↓
Sequence: Ogden (Jan 19) → Provo (Jan 20)
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
Contemporaneous reporting explains that an inversion was trapping PM2.5 across northern Utah during the exact event window.
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
77.5 µg/m³ near Provo
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 2004-01-16 to 2004-01-23 · PM2.5 target: Ogden
26% above nearby days
16% higher than surrounding days
Pollution fingerprint
Metro-wide median of reporting monitors PM2.5 69 µg/m³
26% higher than surrounding days
Before54.9 µg/m³ Event69 µg/m³ After46.4 µg/m³
PM10 88.5 µg/m³
16% higher than surrounding days
Before75 µg/m³ Event88.5 µg/m³ After60 µg/m³
Carbon monoxide 1.61 ppm
22% higher than surrounding days
Before1.47 ppm Event1.61 ppm After1.17 ppm
Nitrogen dioxide 49.1 ppb
About the same as surrounding days
Before46.3 ppb Event49.1 ppb After42 ppb
Sulfur dioxide 2.31 ppb
36% lower than surrounding days
Before4.63 ppb Event2.31 ppb After3.75 ppb
Atmospheric conditions
Nearby EPA weather observationsAbout the same as surrounding days
6% higher than surrounding days
Provo-Orem, UT
Monitor comparison window 2004-01-16 to 2004-01-23 · PM2.5 target: Lindon
16% above nearby days
18% higher than surrounding days
Pollution fingerprint
Metro-wide median of reporting monitors PM2.5 70.3 µg/m³
16% higher than surrounding days
Before51 µg/m³ Event70.3 µg/m³ After58.5 µg/m³
PM10 86.3 µg/m³
18% higher than surrounding days
Before54 µg/m³ Event86.3 µg/m³ After69 µg/m³
Carbon monoxide 1.28 ppm
13% higher than surrounding days
Before1.10 ppm Event1.28 ppm After0.938 ppm
Nitrogen dioxide 45.8 ppb
About the same as surrounding days
Before48 ppb Event45.8 ppb After41.9 ppb
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 |
|---|---|---|---|---|
| Provo-Orem, UT | 77.5 µg/m³ | 3.5 | Jan 20, 2004 | #15 of its top days |
| Ogden-Clearfield, UT | 71.6 µg/m³ | 3.3 | Jan 19, 2004 | #7 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.
The Daily Universe, January 20, 2004
Brigham Young University
Contemporaneous reporting explains that an inversion was trapping PM2.5 across northern Utah during the exact event window.
What it supports
A retained source supports the attributed cause for the stated place and dates.
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.