Wildfire smoke
2020-09-17 2-area wildfire-smoke episode
Daily PM2.5 peaked at 46.9 µg/m³ near Denver across 2 covered metros home to 3.8 million people.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 1.8 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 6.9 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: Colorado Springs (Sep 17) → Denver (Sep 18)
Affected metros
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| Denver-Aurora-Lakewood, CO | 46.9 µg/m³ | 2.1 | Sep 18, 2020 | #23 of its top days |
| Colorado Springs, CO | 29.5 µg/m³ | 2.6 | Sep 17, 2020 | #12 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 IT — Wildfire-U. S. EPA AQS carries an agency-submitted informational qualifier (IT, Wildfire-U. S.) on 4 PM2.5 samples in the candidate CBSA on 2020-09-18, 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.
NWS Air Quality Alert 2
- Air Quality Alert AQABOU An archived NWS Air Quality Alert for Denver-Aurora-Lakewood, CO, issued 2020-09-17T15:10Z, explicitly identifies wildfire smoke. IEM is the archive, not the official system of record.
- Air Quality Alert AQAPUB An archived NWS Air Quality Alert for Colorado Springs, CO, issued 2020-09-17T15:10Z, explicitly identifies wildfire smoke. IEM is the archive, not the official system of record.
Agency and publisher pages 2
- Air Quality Unhealthy For Everyone As Wildfire Smoke Gets Worse In Colorado Contemporaneous reporting says thick, mainly out-of-state wildfire smoke caused unhealthy air and poor visibility in the Denver metro area under a state health advisory.
- Out-Of-State Wildfire Smoke Takes A Crazy Route To Colorado Report describes West Coast wildfire smoke arriving at the Colorado Front Range and combining with in-state smoke to create unhealthy conditions.
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.