Wildfire smoke
2020-08-21 2-area wildfire-smoke episode
Daily PM2.5 peaked at 71.5 µg/m³ near Salt Lake City across 2 covered metros home to 2.0 million people.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 2.8 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 5.4 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.
Sequence: Salt Lake City (Aug 21) → Ogden (Aug 21)
Affected metros
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| Salt Lake City, UT | 71.5 µg/m³ | 3.3 | Aug 21, 2020 | #23 of its top days |
| Ogden-Clearfield, UT | 63.8 µg/m³ | 2.9 | Aug 21, 2020 | #13 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 3
- AQS PM2.5 qualifier RT — Wildfire-U. S. EPA AQS carries an agency-submitted request-exclusion qualifier (RT, Wildfire-U. S.) on 42 PM2.5 samples in the candidate CBSA on 2020-08-21, 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.
- AQS PM2.5 qualifier IT — Wildfire-U. S. EPA AQS carries an agency-submitted informational qualifier (IT, Wildfire-U. S.) on 142 PM2.5 samples in the candidate CBSA on 2020-08-21, 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 49 PM2.5 samples in the candidate CBSA on 2020-08-21, 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.
Agency and publisher pages 2
- Air Quality Technical Report: Hot-spot Analysis Technical report documents a Salt Lake City PM2.5 peak on August 21, 2020 and NOAA smoke-map evidence that winds transported smoke from central and northern California wildfires into Utah.
- Here’s why the air will be smoky across Utah the next few days Contemporaneous local reporting, citing National Weather Service information, reported California and Nevada wildfire smoke reaching northern Utah and degrading Wasatch Front air quality.
What remains uncertain
- An AQS informational qualifier is an official submitting-agency flag, not an EPA-concurred exclusion determination.
- The supplied evidence resolves cause but does not establish identity with another candidate episode.
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.