Mixed causes
2025-03-11 mixed causes episode affecting Chattanooga, TN-GA
Daily PM2.5 peaked at 97.8 µg/m³ near Chattanooga across 1 covered metro home to 588,050 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 ≈ 6.2 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 3.7 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
The supplied retained evidence explicitly supports multiple material causes (prescribed-fire smoke and wildfire smoke) for this episode, so it is retained as mixed.
Affected metros
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| Chattanooga, TN-GA | 97.8 µg/m³ | 7.2 | Mar 12, 2025 | #2 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 IM — Prescribed Fire. EPA AQS carries an agency-submitted informational qualifier (IM, Prescribed Fire.) on 2 PM2.5 samples in the candidate CBSA on 2025-03-12, identifying prescribed-fire 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 2025-03-12, 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 IM — Prescribed Fire. EPA AQS carries an agency-submitted informational qualifier (IM, Prescribed Fire.) on 3 PM2.5 samples in the candidate CBSA on 2025-03-11, identifying prescribed-fire smoke as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
What remains uncertain
- The supplied evidence does not quantify the relative contribution of each supported cause.
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.