Temperature inversion Likely
Daily PM2.5 peaked at 95.2 µg/m³ near Provo 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 ≈ 6.0 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 16 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
Peer-reviewed and contemporaneous meteorological sources identify a Great Salt Lake Valley cold pool/inversion with elevated PM2.5 during the exact event window.
Likely Applicable reporting or a supported inference makes this the best current causal explanation.
PubMed / U.S. EPA authors · Nov 1, 2021 corroborates
The EPA-authored paper identifies elevated PM2.5 associated with cold-pool development in the Great Salt Lake Valley during the January 2013 episode.
Utah Public Radio · Apr 29, 2013 corroborates
Reports that PM2.5 exceeded 70 µg/m3 on January 9, 2013, corroborating the late portion of the Wasatch Front episode; it does not assign a specific emissions source.
See every retained source and limitation ↓
Sequence: Provo (Jan 6) → Salt Lake City (Jan 8) → Ogden (Jan 8)
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
The EPA-authored paper identifies elevated PM2.5 associated with cold-pool development in the Great Salt Lake Valley during the January 2013 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
Reports that PM2.5 exceeded 70 µg/m3 on January 9, 2013, corroborating the late portion of the Wasatch Front episode; it does not assign a specific emissions source.
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.
Provo-Orem, UT
Monitor comparison window 2013-01-03 to 2013-01-12 · PM2.5 target: Lindon
61% above nearby days
47% higher than surrounding days
61% higher than surrounding days
47% higher than surrounding days
32% higher than surrounding days
22% higher than surrounding days
20% lower than surrounding days
About the same as surrounding days
36% higher than surrounding days
Ogden-Clearfield, UT
Monitor comparison window 2013-01-03 to 2013-01-12 · PM2.5 target: Ogden
89% above nearby days
12% lower than surrounding days
58% higher than surrounding days
89% higher than surrounding days
58% higher than surrounding days
9% higher than surrounding days
14% higher than surrounding days
20% higher than surrounding days
14% lower than surrounding days
About the same as surrounding days
About the same as surrounding days
43% higher than surrounding days
12% lower than surrounding days
Salt Lake City, UT
Monitor comparison window 2013-01-03 to 2013-01-12 · PM2.5 target: Hawthorne
17% above nearby days
8% lower than surrounding days
22% higher than surrounding days
17% higher than surrounding days
22% higher than surrounding days
24% higher than surrounding days
6% higher than surrounding days
27% higher than surrounding days
42% lower than surrounding days
About the same as surrounding days
About the same as surrounding days
39% higher than surrounding days
8% lower 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.
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 |
|---|---|---|---|---|
| Provo-Orem, UT | 95.2 µg/m³ | 12.4 | Jan 8, 2013 | #5 of its top days |
| Salt Lake City, UT | 72.8 µg/m³ | 3.3 | Jan 8, 2013 | #20 of its top days |
| Ogden-Clearfield, UT | 71.8 µg/m³ | 6.5 | Jan 9, 2013 | #6 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.
PubMed / U.S. EPA authors
The EPA-authored paper identifies elevated PM2.5 associated with cold-pool development in the Great Salt Lake Valley during the January 2013 episode.
A retained source supports the attributed cause for the stated place and dates.
The paper illustrates the regional mechanism rather than apportioning emissions.
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.