NCAR corroborates
When a good air mass goes bad
NCAR explains the January 2013 Utah pollution episode as a cold-air pool that trapped emissions in the valleys.
Temperature inversion High confidence
2013-01-19 to 2013-01-25 Ogden-Clearfield, UT and Provo-Orem, UT temperature-inversion pollution episode
Daily PM2.5 peaked at 129.5 µg/m³ near Provo across 2 covered metros home to 1.4 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 ≈ 15.5 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 22 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”
Independent scientific and contemporaneous sources identify the January 2013 Wasatch Front episode as a persistent cold-air-pool inversion that trapped locally emitted PM2.5.
High confidence At least two independent causal origins and evidence families agree on this cause.
CBS News corroborates
Salt Lake City smothered by smog
Contemporaneous reporting attributes the January 2013 Wasatch Front pollution to an inversion trapping emissions in the valleys.
NASA Science · Jan 29, 2013 corroborates
Earth Indicator: 130 Micrograms of Particulate Pollution per Cubic Meter in Salt Lake City
Documents the January 23, 2013 Salt Lake Valley PM peak during a strong temperature inversion, materially corroborating inversion confinement within this meteorologically connected Wasatch Front episode; it does not apportion emissions sources.
See every retained source and limitation ↓
Sequence: Provo (Jan 19) → Ogden (Jan 25)
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
NCAR explains the January 2013 Utah pollution episode as a cold-air pool that trapped emissions in the valleys.
View supporting source ↗ - 2Documented
Air-mass movement
Transport into the affected region is documented
Documents the January 23, 2013 Salt Lake Valley PM peak during a strong temperature inversion, materially corroborating inversion confinement within this meteorologically connected Wasatch Front episode; it does not apportion emissions sources.
View transport source ↗ - 3Documented
Local response
129.5 µg/m³ near Provo
EPA monitors recorded the event across 2 metros. The peak daily concentration is roughly 5.9 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.
Provo-Orem, UT
Monitor comparison window 2013-01-16 to 2013-01-28 · PM2.5 target: Lindon
57% above nearby days
41% higher than surrounding days
Pollution fingerprint
Metro-wide median of reporting monitors PM2.5 94.3 µg/m³
57% higher than surrounding days
Before45.4 µg/m³ Event94.3 µg/m³ After8.20 µg/m³
PM10 110 µg/m³
41% higher than surrounding days
Before55 µg/m³ Event110 µg/m³ After13 µg/m³
Carbon monoxide 1.37 ppm
23% higher than surrounding days
Before0.938 ppm Event1.37 ppm After0.338 ppm
Nitrogen dioxide 61.5 ppb
18% higher than surrounding days
Before45.2 ppb Event61.5 ppb After21.6 ppb
Ozone 0.012 ppm
16% higher than surrounding days
Before0.010 ppm Event0.012 ppm After0.022 ppm
Atmospheric conditions
Nearby EPA weather observationsAbout the same as surrounding days
24% lower than surrounding days
Ogden-Clearfield, UT
Monitor comparison window 2013-01-16 to 2013-01-28 · PM2.5 target: Ogden
0% above nearby days
About the same as surrounding days
About the same as surrounding days
Pollution fingerprint
Metro-wide median of reporting monitors PM2.5 34.3 µg/m³
About the same as surrounding days
Before34.6 µg/m³ Event34.3 µg/m³ After12.7 µg/m³
PM10 50 µg/m³
About the same as surrounding days
Before50 µg/m³ Event50 µg/m³ After16 µg/m³
Carbon monoxide 0.543 ppm
9% lower than surrounding days
Before0.669 ppm Event0.543 ppm After0.648 ppm
Nitrogen dioxide 34.3 ppb
About the same as surrounding days
Before47 ppb Event34.3 ppb After19.1 ppb
Sulfur dioxide 1.79 ppb
About the same as surrounding days
Before1.67 ppb Event1.79 ppb After1.29 ppb
Ozone 0.011 ppm
About the same as surrounding days
Before0.010 ppm Event0.011 ppm After0.024 ppm
Atmospheric conditions
Nearby EPA weather observationsAbout the same as surrounding days
About the same as surrounding days
11% lower 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.
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 | 129.5 µg/m³ | 28.7 | Jan 23, 2013 | Worst day on record |
| Ogden-Clearfield, UT | 66 µg/m³ | 3.0 | Jan 25, 2013 | #10 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.
When a good air mass goes bad
NCAR
NCAR explains the January 2013 Utah pollution episode as a cold-air pool that trapped emissions in the valleys.
What it supports
A retained source supports the attributed cause for the stated place and dates.
Salt Lake City smothered by smog
CBS News
Contemporaneous reporting attributes the January 2013 Wasatch Front pollution to an inversion trapping emissions in the valleys.
What it supports
A retained source supports the attributed cause for the stated place and dates.
What remains uncertain
- The retained evidence is scoped to the places and dates stated; it is not a catalog promotion.
Status and provenance
High confidence At least two independent causal origins and evidence families agree on this cause.
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.