Wildfire smoke
2023 late-July Canadian wildfire-smoke episode
Daily PM2.5 peaked at 59.1 µg/m³ near Madison across 3 covered metros home to 3.5 million 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 ≈ 1.9 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 6.5 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 supplied evidence supports wildfire smoke for this event. It is grouped with 1 other supplied event because the evidence identifies Canada as the shared origin and the affected intervals form one continuous 2023-07-24 through 2023-07-25 occurrence. Qualified supplied evidence supports wildfire smoke for this event. It is grouped with 1 other supplied event because the evidence identifies Canada as the shared origin and the affected intervals form one continuous 2023-07-24 through 2023-07-25 occurrence.
Sequence: Madison (Jul 24) → Milwaukee (Jul 24) → Grand Rapids (Jul 25)
Affected metros
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| Madison, WI | 59.1 µg/m³ | 2.7 | Jul 24, 2023 | #9 of its top days |
| Milwaukee-Waukesha-West Allis, WI | 49.8 µg/m³ | 2.3 | Jul 24, 2023 | #16 of its top days |
| Grand Rapids-Wyoming, MI | 46.8 µg/m³ | 2.1 | Jul 25, 2023 | #23 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 4
- AQS PM2.5 qualifier IF — Fire - Canadian. EPA AQS carries an agency-submitted informational qualifier (IF, Fire - Canadian.) on 48 PM2.5 samples in the candidate CBSA on 2023-07-24, 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 IF — Fire - Canadian. EPA AQS carries an agency-submitted informational qualifier (IF, Fire - Canadian.) on 96 PM2.5 samples in the candidate CBSA on 2023-07-24, 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 RF — Fire - Canadian. EPA AQS carries an agency-submitted request-exclusion qualifier (RF, Fire - Canadian.) on 48 PM2.5 samples in the candidate CBSA on 2023-07-25, 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 IF — Fire - Canadian. EPA AQS carries an agency-submitted informational qualifier (IF, Fire - Canadian.) on 48 PM2.5 samples in the candidate CBSA on 2023-07-25, 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.
Agency and publisher pages 2
- Exceptional Event Demonstration for 2023 PM2.5 Episodes EGLE’s exceptional-event demonstration finds a clear causal relationship between Canadian wildfire emissions transported to the Grand Rapids monitor and the July 25–26, 2023 PM2.5 episode.
- Wildfire smoke from Canada triggers air quality alert in Michigan Contemporaneous reporting said Canadian wildfire smoke was moving through Michigan on July 25 and prompted an Air Quality Action Day.
News discovery (GDELT) 1
- Milwaukee air quality: Wisconsin DNR issues warning for wildfire smoke The contemporaneous title explicitly attributes Wisconsin's Milwaukee air-quality warning to wildfire smoke; the page could not be retrieved.
What remains uncertain
- Agency-submitted AQS qualifiers are causal flags but 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.