Winter inversion
2002-02-06 winter inversion episode affecting Salt Lake City, UT, Ogden-Clearfield, UT
Daily PM2.5 peaked at 100.2 µg/m³ near Ogden across 2 covered metros home to 2.0 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 ≈ 6.2 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 12 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.
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.
What happened, in the record
Qualified frozen evidence supports winter inversion as the broad root cause.
Sequence: Salt Lake City (Feb 6) → Ogden (Feb 7)
Affected metros
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| Ogden-Clearfield, UT | 100.2 µg/m³ | 4.6 | Feb 7, 2002 | Worst day on record |
| Salt Lake City, UT | 91.6 µg/m³ | 8.0 | Feb 7, 2002 | #2 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.
The evidence
Agency and publisher pages 1
- Continuous Determination of Fine Particulate Matter Mass in the Salt Lake City Environmental Monitoring Project: A Comparison of Real-Time and Conventional TEOM Monitor Results The study's 2002 Winter Olympic monitoring discussion identifies February 7 as a time of strong inversion, corroborating an inversion condition during this Salt Lake City–Ogden event; it does not apportion emissions sources.
What remains uncertain
- The evidence supports regional influence or transport but does not quantify the contribution to observed PM2.5.
Status and provenance
Research preview: this record carries research-only status and its boundaries, cause, and name may change as evidence review completes. Grouping policy common_sense_root_cause_grouping.v2. The cause label reflects the assembled evidence above, not an IAQng detection formula.