Other
January 2000 San Joaquin Valley limited-dispersion pollution episode
Daily PM2.5 peaked at 160 µg/m³ near Fresno across 2 covered metros home to 2.1 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 ≈ 8.5 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 18 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
District evidence identifies a valley-wide January 7–10 episode; the Fresno evidence independently describes the same January episode as accumulated local primary and secondary pollution under limited dispersion. District and measurement-study evidence identify the January 7–10/2–12 San Joaquin Valley winter episode, including the January 9 Fresno maximum and January 7 Bakersfield impacts.
Sequence: Bakersfield (Jan 7) → Fresno (Jan 9)
Affected metros
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| Fresno, CA | 160 µg/m³ | 13.1 | Jan 9, 2000 | #4 of its top days |
| Bakersfield, CA | 102.5 µg/m³ | 4.7 | Jan 7, 2000 | #22 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 2
- Historical Meteorological Analysis in Support of the 2003 San Joaquin Valley PM10 State Implementation Plan: Final Report The district's retrospective analysis identifies a valley-wide January 7-10, 2000 PM2.5 episode, including Bakersfield sites, in which primary and secondary pollutants from local emissions accumulated under limited dispersion; it describes strong stability, limited mixing, and nitrate/sulfate formation conditions.
- A wintertime PM2.5 episode at the Fresno, CA, supersite A measurement study examined the January 2-12 Fresno episode, whose winter maximum occurred January 9, and found evidence consistent with shallow radiation-layer accumulation of urban primary emissions and rapid secondary nitrate formation after daytime coupling to a valley-wide layer.
What remains uncertain
- The records describe contributing local emissions and secondary formation, not a single named emitting facility or fire.
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.