Wildfire smoke
1999-10-20 wildfire smoke episode affecting Sacramento--Roseville--Arden-Arcade, CA, San Jose-Sunnyvale-Santa Clara, CA
Daily PM2.5 peaked at 90 µg/m³ near Sacramento across 2 covered metros home to 4.5 million people.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 3.3 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 15 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 wildfire smoke as the broad root cause.
Sequence: Sacramento (Oct 20) → San Jose (Oct 21)
Affected metros
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| Sacramento--Roseville--Arden-Arcade, CA | 90 µg/m³ | 4.1 | Oct 20, 1999 | #22 of its top days |
| San Jose-Sunnyvale-Santa Clara, CA | 69.3 µg/m³ | 3.1 | Oct 21, 1999 | #19 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
EPA AQS monitor qualifier 1
- AQS PM2.5 qualifier E — Forest Fire. EPA AQS carries an agency-submitted request-exclusion qualifier (E, Forest Fire.) on 4 PM2.5 samples in the candidate CBSA on 1999-10-21, identifying wildfire smoke as affecting the samples. A request-exclusion qualifier is an official submitting-agency causal claim, but this endpoint does not establish EPA concurrence.
What remains uncertain
- AQS qualifiers are submitting-agency causal flags and do not by themselves establish EPA concurrence.
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.