Stagnant pollution mixture Possible
Daily PM2.5 peaked at 58.3 µg/m³ near Ogden across 1 covered metro home to 667,681 people.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 2.3 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 1.5 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
Certified observations show a broad Ogden particle episode across five PM2.5 monitors, with PM10, carbon monoxide, nitrogen dioxide, and sulfur dioxide elevated from the earlier comparison window. The nearest official surface station recorded 12 calm hours, 16 hours at or below three knots, 22 hours with visibility at or below three miles, and haze. This supports weak-dispersion accumulation of a mixed pollution burden, but it does not identify source-sector shares or prove a temperature inversion.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
National Weather Service surface observations via Iowa Environmental Mesonet hypothesis
The nearest official station recorded 12 calm hours, 16 of 24 observed hours with wind at or below three knots, visibility at or below three miles for 22 hours, mist throughout the day, and one haze observation.
U.S. EPA AirData hypothesis
EPA records show median daily PM2.5 of 55.9 micrograms per cubic meter across five Ogden-area monitors, compared with 25.5 on the preceding sampled day. PM10, carbon monoxide, nitrogen dioxide, and sulfur dioxide were also higher than the earlier comparison window.
Inference, not direct attribution
official_surface_weak_dispersion_multimonitor_accumulation.v1: This inference is recorded in the catalog methodology.
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
official_surface_weak_dispersion_multimonitor_accumulation.v1. This inference is recorded in the catalog methodology.
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 1 metro. The peak daily concentration is roughly 2.6 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 “Stagnant pollution mixture” explanation; it does not assign the cause by itself.
Ogden-Clearfield, UT
Monitor comparison window 2002-01-05 to 2002-01-11 · PM2.5 target: Ogden
29% above nearby days
39% higher than surrounding days
29% higher than surrounding days
39% higher than surrounding days
12% higher than surrounding days
5% higher than surrounding days
10% 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 | 58.3 µg/m³ | 2.6 | Jan 8, 2002 | #20 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.
National Weather Service surface observations via Iowa Environmental Mesonet
The nearest official station recorded 12 calm hours, 16 of 24 observed hours with wind at or below three knots, visibility at or below three miles for 22 hours, mist throughout the day, and one haze observation.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
Fog and restricted visibility are not themselves particle attribution, and the surface record does not directly measure the vertical temperature profile.
U.S. EPA AirData
EPA records show median daily PM2.5 of 55.9 micrograms per cubic meter across five Ogden-area monitors, compared with 25.5 on the preceding sampled day. PM10, carbon monoxide, nitrogen dioxide, and sulfur dioxide were also higher than the earlier comparison window.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The fingerprint demonstrates a broad mixed episode but cannot apportion PM2.5 among mobile, residential, industrial, secondary, or transported sources.
Utah Department of Environmental Quality
Utah DEQ explains that weak wind and winter valley trapping allow locally and regionally emitted precursors to form and accumulate PM2.5, with secondary ammonium nitrate often dominating inversion-period mass.
Context for the event; this item does not establish the attributed cause by itself.
This is a recurring Wasatch Front profile, not an assessment of January 8, 2002.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
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.