Wildfire smoke
2023 mid-July Canadian wildfire-smoke episode
Daily PM2.5 peaked at 67.2 µg/m³ near Des Moines across 18 covered metros home to 32 million people. 10 metros 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 ≈ 2.2 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 70 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 8 other supplied events because the evidence identifies Canada as the shared origin and the affected intervals form one continuous 2023-07-15 through 2023-07-18 occurrence. Qualified supplied evidence supports wildfire smoke for this event. It is grouped with 8 other supplied events because the evidence identifies Canada as the shared origin and the affected intervals form one continuous 2023-07-15 through 2023-07-18 occurrence. Qualified supplied evidence supports wildfire smoke for this event. It is grouped with 8 other supplied events because the evidence identifies Canada as the shared origin and the affected intervals form one continuous 2023-07-15 through 2023-07-18 occurrence. Qualified supplied e
Sequence: Des Moines (Jul 15) → Minneapolis (Jul 15) → Chicago (Jul 16) → Cleveland (Jul 17) → Columbus (Jul 17) → Akron (Jul 17) → Knoxville (Jul 17) → Winston (Jul 17) → Chattanooga (Jul 17) → Rochester (Jul 17) → +8 more metros
Affected metros
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| Des Moines-West Des Moines, IA | 67.2 µg/m³ | 5.2 | Jul 16, 2023 | #3 of its top days |
| Cleveland-Elyria, OH | 63.5 µg/m³ | 2.9 | Jul 17, 2023 | #8 of its top days |
| Chicago-Naperville-Elgin, IL-IN-WI | 58.8 µg/m³ | 2.7 | Jul 16, 2023 | #23 of its top days |
| Columbus, OH | 58.7 µg/m³ | 2.7 | Jul 17, 2023 | #9 of its top days |
| Akron, OH | 58.6 µg/m³ | 2.7 | Jul 17, 2023 | #5 of its top days |
| Knoxville, TN | 54.8 µg/m³ | 2.5 | Jul 17, 2023 | #19 of its top days |
| Winston-Salem, NC | 54.2 µg/m³ | 4.6 | Jul 17, 2023 | #5 of its top days |
| Chattanooga, TN-GA | 53.5 µg/m³ | 2.4 | Jul 17, 2023 | #6 of its top days |
| Minneapolis-St. Paul-Bloomington, MN-WI | 51.4 µg/m³ | 2.3 | Jul 15, 2023 | #23 of its top days |
| Rochester, NY | 49.9 µg/m³ | 2.3 | Jul 17, 2023 | #5 of its top days |
| Dayton, OH | 48.2 µg/m³ | 2.2 | Jul 17, 2023 | #14 of its top days |
| Charlotte-Concord-Gastonia, NC-SC | 46.1 µg/m³ | 4.1 | Jul 18, 2023 | #6 of its top days |
| Greenville-Anderson-Mauldin, SC | 45.8 µg/m³ | 4.1 | Jul 18, 2023 | #9 of its top days |
| Raleigh, NC | 45.6 µg/m³ | 2.1 | Jul 18, 2023 | #7 of its top days |
| Syracuse, NY | 43.7 µg/m³ | 2.0 | Jul 17, 2023 | #11 of its top days |
| Columbia, SC | 40.4 µg/m³ | 1.8 | Jul 18, 2023 | #15 of its top days |
| Greensboro-High Point, NC | 40.3 µg/m³ | 3.6 | Jul 17, 2023 | #19 of its top days |
| Durham-Chapel Hill, NC | 36.7 µg/m³ | 1.7 | Jul 18, 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 25
- AQS PM2.5 qualifier IT — Wildfire-U. S. EPA AQS carries an agency-submitted informational qualifier (IT, Wildfire-U. S.) on 320 PM2.5 samples in the candidate CBSA on 2023-07-15, 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 408 PM2.5 samples in the candidate CBSA on 2023-07-16, 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 IF — Fire - Canadian. EPA AQS carries an agency-submitted informational qualifier (IF, Fire - Canadian.) on 193 PM2.5 samples in the candidate CBSA on 2023-07-17, 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 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 2023-07-17, 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 RF — Fire - Canadian. EPA AQS carries an agency-submitted request-exclusion qualifier (RF, Fire - Canadian.) on 49 PM2.5 samples in the candidate CBSA on 2023-07-17, 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 49 PM2.5 samples in the candidate CBSA on 2023-07-17, 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 IF — Fire - Canadian. EPA AQS carries an agency-submitted informational qualifier (IF, Fire - Canadian.) on 50 PM2.5 samples in the candidate CBSA on 2023-07-17, 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 IF — Fire - Canadian. EPA AQS carries an agency-submitted informational qualifier (IF, Fire - Canadian.) on 51 PM2.5 samples in the candidate CBSA on 2023-07-17, 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 IF — Fire - Canadian. EPA AQS carries an agency-submitted informational qualifier (IF, Fire - Canadian.) on 53 PM2.5 samples in the candidate CBSA on 2023-07-17, 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 RF — Fire - Canadian. EPA AQS carries an agency-submitted request-exclusion qualifier (RF, Fire - Canadian.) on 24 PM2.5 samples in the candidate CBSA on 2023-07-17, 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 96 PM2.5 samples in the candidate CBSA on 2023-07-18, 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.
- AQS PM2.5 qualifier IF — Fire - Canadian. EPA AQS carries an agency-submitted informational qualifier (IF, Fire - Canadian.) on 97 PM2.5 samples in the candidate CBSA on 2023-07-18, 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.
- +13 more EPA AQS records on file
NWS Air Quality Alert 2
- Archived Iowa Air Quality Alert, July 16, 2023 Iowa DNR explicitly identified Canadian wildfire smoke affecting the Des Moines-area episode through July 16. IEM is the archive, not the official system of record.
- Archived Chicago Air Quality Alert, July 16, 2023 Illinois EPA alerts explicitly identified wildfire smoke affecting Chicago during the event. IEM is the archive, not the official system of record.
Agency and publisher pages 7
- Exceptional Events Demonstration for the Wildfire Smoke-Driven PM2.5 Episode on July 17, 2023, in the Toledo, OH MSA Ohio EPA describes Canadian wildfire smoke moving into the Ohio Valley and building at the surface across northern Ohio on July 16–17.
- Ohio’s Exceptional Events Demonstration for 2023 Ohio EPA concludes the July 16–17 Great Lakes and northeastern-Ohio episode was transported Canadian wildfire smoke rather than a local source.
- Unhealthy Air Possible in NC This Week Due to Canadian Wildfires North Carolina DEQ reported that a plume of smoke from Canadian wildfires was entering the state and forecast unhealthy fine-particle conditions for central and western North Carolina.
- DNR Issues Statewide Air Quality Advisory Due To Canadian Wildfire Smoke Wisconsin DNR forecast smoke from western Canadian wildfires across the Upper Midwest for July 14–16.
- Illinois Officials Expand Air Quality Messaging to Educate Residents and Encourage Actions to Protect Public Health Illinois officials reported that wildfire smoke had caused unusually severe Illinois air-quality conditions in recent weeks.
- Federal Agency Issues New Air Quality Alerts Targeting Much of Northern US Contemporaneous reporting of the National Weather Service forecast says Canadian-Prairie smoke was directed into the Lower 48 and that air-quality alerts included central Tennessee.
- Air quality health advisories in effect across New York on Monday due to Canadian wildfire smoke Contemporaneous coverage reports statewide New York health advisories as smoke from Canadian wildfires returned to the state.
News discovery (GDELT) 1
- Air quality starts improving and humidity drops Monday KCCI reported unhealthy air and ground-level smoke across central Iowa on July 16 and explained that changing winds would shift transport away from Canadian fires.
What remains uncertain
- Agency-submitted AQS qualifiers are causal flags but do not by themselves establish EPA concurrence.
- The resolution relies on qualified transport, grouping, observation, or impact evidence rather than a direct cause-attribution record.
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.