Mixed causes Likely
Daily PM2.5 peaked at 60.6 µg/m³ near Detroit across 1 covered metro home to 4.4 million people.
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 ≈ 9.7 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.
Why we think this happened
EPA's exact-period account attributes the June 20-28 regional event to man-made pollution plus some smoke and places the aerosol buildup in the Midwest before transport east. Detroit on June 24 fits that documented regional episode.
Likely Applicable reporting or a supported inference makes this the best current causal explanation.
U.S. Environmental Protection Agency / Federal Register · Jan 30, 2004 official
EPA describes the June 20-28, 2002 Central and Eastern U.S. haze event as a combination of man-made pollutants and some smoke, with aerosol buildup in the Midwest followed by transport into the Northeast.
Evidence path
A cause is more convincing when the record connects three things: something happened, the air mass moved toward the region, and local instruments responded. Here is how much of that chain is documented for this event.
Source or mechanism
EPA describes the June 20-28, 2002 Central and Eastern U.S. haze event as a combination of man-made pollutants and some smoke, with aerosol buildup in the Midwest followed by transport into the Northeast.
View supporting source ↗Air-mass movement
The retained record does not yet show how air traveled from the proposed source to these metros. A trajectory replay or dated plume analysis belongs here.
Local response
EPA monitors recorded the event across 1 metro. The peak daily concentration is roughly 2.8 cigarette-equivalents at the outdoor daily rate.
Inspect the pollutant and weather signals ↓Event autopsy
Before, during, and after the episode: nearby pollutant monitors and surface-weather stations show what changed. This context tests the “Mixed causes” explanation; it does not assign the cause by itself.
Detroit-Warren-Dearborn, MI
Monitor comparison window 2002-06-21 to 2002-06-27 · PM2.5 target: DET-LINWOOD
71% above nearby days
12% lower than surrounding days
41% higher than surrounding days
71% higher than surrounding days
41% higher than surrounding days
49% higher than surrounding days
14% higher than surrounding days
35% higher than surrounding days
8% higher than surrounding days
15% lower than surrounding days
About the same as surrounding days
6% higher than surrounding days
12% lower than surrounding days
Source: U.S. EPA AirData daily observations and, where available, nearby ASOS/AWOS surface observations. Values are descriptive medians over the retained monitor set; missing measurements remain missing. Transport and source evidence remain separate layers because this instrument pattern does not assign a cause by itself.
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.
Views from the selected metro
Select a metro on the map to see nearby cameras. Where an operator archive reaches the event, drag the divider to compare two moments, adjust either date and time, or play the available event-day frames. Camera imagery is visual context, not an air-quality measurement or proof of smoke.
No useful public camera views are currently available within 80 km of this metro.
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| Detroit-Warren-Dearborn, MI | 60.6 µg/m³ | 2.8 | Jun 24, 2002 | #16 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.
Public evidence library
Each card states what a source supports—and what it does not. Official records, research, reporting, community observations, and transparent inferences remain visibly different kinds of evidence.
U.S. Environmental Protection Agency / Federal Register
EPA describes the June 20-28, 2002 Central and Eastern U.S. haze event as a combination of man-made pollutants and some smoke, with aerosol buildup in the Midwest followed by transport into the Northeast.
An official source supports the attributed cause for the stated place and dates.
The regional account does not apportion Detroit's daily mass between anthropogenic pollution and smoke or name a fire.
Likely Applicable reporting or a supported inference makes this the best current causal explanation.
This episode was grouped from the monitor record by the catalog pipeline and given its cause from the evidence listed above. It has not been individually reviewed and signed off, so its boundaries, cause, and name may change as evidence accumulates. Grouping policy common_sense_root_cause_grouping.v2. The cause label reflects the assembled evidence above, not an IAQng detection formula. If it is wrong, tell us.