Temperature inversion Likely
Daily PM2.5 peaked at 86.6 µg/m³ near Salt Lake City across 3 covered metros home to 2.7 million people. 2 metros 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 ≈ 11.0 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 30 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
Manual research connected 2 source events to one temperature-inversion pollution episode using the deterministic grouping rule.
Likely Applicable reporting or a supported inference makes this the best current causal explanation.
KSL / Associated Press · Jan 30, 2007 corroborates
Contemporaneous reporting says a Wasatch Front inversion trapped exhaust and particles from factories, furnaces, and fireplaces during the supplied January 26-30 episode.
KSL · Jan 30, 2007 corroborates
KSL reported on January 30 that northern Utah's valleys were under a persistent inversion trapping car exhaust, industrial emissions, furnace particles, and fireplace smoke, with unhealthy air persisting through much of January.
Daily Kos · Jan 27, 2007 hypothesis
An exact-date community account independently describes the prolonged Salt Lake inversion and Code Red PM2.5 conditions on January 26-27.
See every retained source and limitation ↓
Sequence: Salt Lake City (Jan 26) → Ogden (Jan 27) → Provo (Jan 27)
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 Wasatch Front inversion trapped exhaust and particles from factories, furnaces, and fireplaces during the supplied January 26-30 episode.
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
EPA monitors recorded the event across 3 metros. The peak daily concentration is roughly 3.9 cigarette-equivalents at the outdoor daily rate.
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 “Temperature inversion” explanation; it does not assign the cause by itself.
Salt Lake City, UT
Monitor comparison window 2007-01-23 to 2007-02-02 · PM2.5 target: Hawthorne
24% above nearby days
About the same as surrounding days
24% higher than surrounding days
About the same as surrounding days
12% higher than surrounding days
14% higher than surrounding days
7% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
Ogden-Clearfield, UT
Monitor comparison window 2007-01-23 to 2007-02-02 · PM2.5 target: Ogden
26% above nearby days
About the same as surrounding days
32% higher than surrounding days
26% higher than surrounding days
32% higher than surrounding days
6% higher than surrounding days
14% higher than surrounding days
11% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
Provo-Orem, UT
Monitor comparison window 2007-01-23 to 2007-02-02 · PM2.5 target: North Provo
12% above nearby days
18% higher than surrounding days
12% higher than surrounding days
18% higher than surrounding days
About 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.
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 |
|---|---|---|---|---|
| Salt Lake City, UT | 86.6 µg/m³ | 18.5 | Jan 27, 2007 | #3 of its top days |
| Ogden-Clearfield, UT | 76.8 µg/m³ | 6.5 | Jan 30, 2007 | #3 of its top days |
| Provo-Orem, UT | 74.8 µg/m³ | 6.7 | Jan 27, 2007 | #21 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.
KSL / Associated Press
Contemporaneous reporting says a Wasatch Front inversion trapped exhaust and particles from factories, furnaces, and fireplaces during the supplied January 26-30 episode.
A retained source supports the attributed cause for the stated place and dates.
The report identifies the trapping mechanism but does not apportion the emissions mixture.
KSL
KSL reported on January 30 that northern Utah's valleys were under a persistent inversion trapping car exhaust, industrial emissions, furnace particles, and fireplace smoke, with unhealthy air persisting through much of January.
A retained source supports the attributed cause for the stated place and dates.
The story discusses northern Utah's multi-valley episode and specifically cites Salt Lake and Davis counties rather than publishing separate Provo and Ogden source apportionment.
Daily Kos
An exact-date community account independently describes the prolonged Salt Lake inversion and Code Red PM2.5 conditions on January 26-27.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
Community reporting corroborates timing and conditions but is not an official attribution.
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.