Wildfire smoke
2020-09-10 8-area wildfire-smoke episode
Daily PM2.5 peaked at 199.3 µg/m³ near Fresno across 8 covered metros home to 28 million people. 1 metro recorded their worst day on record; 8 placed a top-ten day.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 13.8 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 389 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
Supplied qualified evidence supports wildfire-smoke as the root cause. The grouping includes only events linked by explicit shared episode evidence; otherwise this remains a single-event episode. Supplied qualified evidence supports wildfire-smoke as the root cause. The grouping includes only events linked by explicit shared episode evidence; otherwise this remains a single-event episode.
Sequence: San Francisco (Sep 10) → Sacramento (Sep 11) → Stockton (Sep 11) → San Jose (Sep 11) → Fresno (Sep 12) → Los Angeles (Sep 12) → San Diego (Sep 13) → Oxnard (Sep 13)
Affected metros
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| Fresno, CA | 199.3 µg/m³ | 45.8 | Sep 16, 2020 | Worst day on record |
| San Francisco-Oakland-Hayward, CA | 167.7 µg/m³ | 29.1 | Sep 11, 2020 | #2 of its top days |
| Sacramento--Roseville--Arden-Arcade, CA | 147.3 µg/m³ | 23.5 | Sep 11, 2020 | #6 of its top days |
| Stockton-Lodi, CA | 140 µg/m³ | 22.2 | Sep 11, 2020 | #4 of its top days |
| San Jose-Sunnyvale-Santa Clara, CA | 123.1 µg/m³ | 20.2 | Sep 11, 2020 | #3 of its top days |
| Los Angeles-Long Beach-Anaheim, CA | 102.7 µg/m³ | 4.7 | Sep 12, 2020 | #7 of its top days |
| San Diego-Carlsbad, CA | 96.7 µg/m³ | 18.4 | Sep 14, 2020 | #5 of its top days |
| Oxnard-Thousand Oaks-Ventura, CA | 58.7 µg/m³ | 7.2 | Sep 15, 2020 | #4 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
Official records
- NOAA Storm Events Dense Smoke, CALIFORNIA, Sep 9, 2020 "A large area of high pressure over the west brought excessive heat and dry conditions to the region. Numerous record high temperatures were broken with 13 broken records on Sunday the 6th alone including records set that…" record →
EPA AQS monitor qualifier 67
- AQS PM2.5 qualifier IT — Wildfire-U. S. EPA AQS carries an agency-submitted informational qualifier (IT, Wildfire-U. S.) on 95 PM2.5 samples in the candidate CBSA on 2020-09-10, identifying wildfire smoke as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
- AQS PM2.5 qualifier RT — Wildfire-U. S. EPA AQS carries an agency-submitted request-exclusion qualifier (RT, Wildfire-U. S.) on 24 PM2.5 samples in the candidate CBSA on 2020-09-11, 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.
- AQS PM2.5 qualifier IT — Wildfire-U. S. EPA AQS carries an agency-submitted informational qualifier (IT, Wildfire-U. S.) on 24 PM2.5 samples in the candidate CBSA on 2020-09-11, identifying wildfire smoke as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
- AQS PM2.5 qualifier IT — Wildfire-U. S. EPA AQS carries an agency-submitted informational qualifier (IT, Wildfire-U. S.) on 121 PM2.5 samples in the candidate CBSA on 2020-09-11, identifying wildfire smoke as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
- AQS PM2.5 qualifier RT — Wildfire-U. S. EPA AQS carries an agency-submitted request-exclusion qualifier (RT, Wildfire-U. S.) on 24 PM2.5 samples in the candidate CBSA on 2020-09-12, 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.
- AQS PM2.5 qualifier IT — Wildfire-U. S. EPA AQS carries an agency-submitted informational qualifier (IT, Wildfire-U. S.) on 121 PM2.5 samples in the candidate CBSA on 2020-09-14, identifying wildfire smoke as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
- AQS PM2.5 qualifier IT — Wildfire-U. S. EPA AQS carries an agency-submitted informational qualifier (IT, Wildfire-U. S.) on 118 PM2.5 samples in the candidate CBSA on 2020-09-16, identifying wildfire smoke as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
- AQS PM2.5 qualifier IT — Wildfire-U. S. EPA AQS carries an agency-submitted informational qualifier (IT, Wildfire-U. S.) on 216 PM2.5 samples in the candidate CBSA on 2020-09-10, identifying wildfire smoke as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
- AQS PM2.5 qualifier RT — Wildfire-U. S. EPA AQS carries an agency-submitted request-exclusion qualifier (RT, Wildfire-U. S.) on 24 PM2.5 samples in the candidate CBSA on 2020-09-16, 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.
- AQS PM2.5 qualifier IT — Wildfire-U. S. EPA AQS carries an agency-submitted informational qualifier (IT, Wildfire-U. S.) on 217 PM2.5 samples in the candidate CBSA on 2020-09-11, identifying wildfire smoke as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
- AQS PM2.5 qualifier IT — Wildfire-U. S. EPA AQS carries an agency-submitted informational qualifier (IT, Wildfire-U. S.) on 24 PM2.5 samples in the candidate CBSA on 2020-09-17, identifying wildfire smoke as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
- AQS PM2.5 qualifier IT — Wildfire-U. S. EPA AQS carries an agency-submitted informational qualifier (IT, Wildfire-U. S.) on 96 PM2.5 samples in the candidate CBSA on 2020-09-13, identifying wildfire smoke as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
- +55 more EPA AQS records on file
NWS Air Quality Alert 1
- Air Quality Alert AQALOX An archived NWS Air Quality Alert for Los Angeles-Long Beach-Anaheim, CA, issued 2020-09-12T23:45Z, explicitly identifies wildfire smoke. IEM is the archive, not the official system of record.
Agency and publisher pages 4
- Air quality advisory for wildfire smoke through Friday Bay Area regulator identified wildfire smoke as the basis for the September 17-18 advisory and described residual smoke aloft after onshore winds pushed smoke out.
- Smoke Advisory: Bobcat and El Dorado Fires Regional air regulator warned that smoke from the Bobcat and El Dorado fires, with possible northern California smoke contribution, could elevate PM2.5 in the South Coast Air Basin.
- Smoke Advisory: Unhealthy Air Quality Declared due to Smoke from Wildfires Burning in the Region Official Southern California advisory confirms widespread September wildfire-smoke impacts but is not a direct assessment of the Bay Area, Sacramento, Stockton, or Fresno monitors.
- Notes from the Field: Understanding Smoke Exposure in Communities and Fire Camps Affected by Wildfires—California and Oregon, 2020 CDC describes high PM2.5 and unhealthy-to-hazardous conditions in California communities near 2020 wildfire incidents, including the Creek Fire area; it does not source-apportion each listed metro measurement.
What remains uncertain
- An AQS informational qualifier is an official submitting-agency flag, not an EPA-concurred exclusion determination.
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.