Winter inversion
2004-01-15 winter inversion episode affecting Provo-Orem, UT, Ogden-Clearfield, UT
Daily PM2.5 peaked at 82.1 µg/m³ near Provo across 2 covered metros home to 1.4 million people. 1 metro 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 ≈ 4.6 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 6.6 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: Provo (Jan 15) → Ogden (Jan 16)
Affected metros
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| Provo-Orem, UT | 82.1 µg/m³ | 7.2 | Jan 16, 2004 | #10 of its top days |
| Ogden-Clearfield, UT | 62.5 µg/m³ | 2.8 | Jan 16, 2004 | #16 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
- Analyses of Individual Nonattainment Area EPA's technical-support analysis identifies a strong inversion across northern Utah during January 1–17, 2004. The event's January 15–16 timing and Wasatch Front locations fall within that documented episode; the assessment describes inversion-driven PM2.5 buildup rather than a single emissions source.
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.