Mixed causes Possible
Daily PM2.5 peaked at 77.8 µg/m³ near Pittsburgh across 3 covered metros home to 4.5 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 ≈ 4.1 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 19 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
Manual research connected 3 source events to one mixed-source pollution episode using the deterministic grouping rule.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
U.S. Environmental Protection Agency official
EPA's review found a widespread sulfate event across the Southeast on June 24, 2005 and found the Kentucky wildfire evidence insufficient for causal attribution. The source supplies regional context only for the June 24 Little Rock and Memphis observations.
NASA Earth Observatory corroborates
NASA describes particle pollution across the Mississippi River Valley and Deep South from June 20 onward, with stable humid air trapping aerosol from vehicles, power plants, and fires; its June 23 satellite image shows the haze over the lower Midwest and Gulf region.
NASA Earth Observatory · Jun 24, 2005 corroborates
NASA documented a broad eastern U.S. haze episode during the event window caused by stable humid conditions retaining particles from vehicles, power plants, and fires.
See every retained source and limitation ↓
Sequence: Little Rock (Jun 23) → Memphis (Jun 23) → Pittsburgh (Jun 25)
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
NASA describes particle pollution across the Mississippi River Valley and Deep South from June 20 onward, with stable humid air trapping aerosol from vehicles, power plants, and fires; its June 23 satellite image shows the haze over the lower…
View supporting source ↗Air-mass movement
NASA describes particle pollution across the Mississippi River Valley and Deep South from June 20 onward, with stable humid air trapping aerosol from vehicles, power plants, and fires; its June 23 satellite image shows the haze over the lower…
View transport source ↗Local response
EPA monitors recorded the event across 3 metros. The peak daily concentration is roughly 3.5 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.
Pittsburgh, PA
Monitor comparison window 2005-06-22 to 2005-06-28 · PM2.5 target: Liberty
37% above nearby days
22% higher than surrounding days
37% higher than surrounding days
22% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
25% higher than surrounding days
Little Rock-North Little Rock-Conway, AR
Monitor comparison window 2005-06-20 to 2005-06-29 · PM2.5 target: CONWAY
12% above nearby days
About the same as surrounding days
12% higher than surrounding days
About the same as surrounding days
11% higher than surrounding days
10% higher than surrounding days
About the same as surrounding days
Memphis, TN-MS-AR
Monitor comparison window 2005-06-20 to 2005-06-29
20% above nearby days
15% higher than surrounding days
20% higher than surrounding days
15% higher than surrounding days
11% higher than surrounding days
About the same as surrounding days
About the same as 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 |
|---|---|---|---|---|
| Pittsburgh, PA | 77.8 µg/m³ | 3.5 | Jun 25, 2005 | #13 of its top days |
| Little Rock-North Little Rock-Conway, AR | 48.5 µg/m³ | 10.0 | Jun 24, 2005 | #2 of its top days |
| Memphis, TN-MS-AR | 44.2 µg/m³ | 5.8 | Jun 24, 2005 | #13 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.
NASA Earth Observatory
NASA documented a broad eastern U.S. haze episode during the event window caused by stable humid conditions retaining particles from vehicles, power plants, and fires.
A retained source supports the attributed cause for the stated place and dates.
Pittsburgh is near the edge of the narrative's named regions and no local source share is given.
NASA Earth Observatory
NASA reported that haze lingering from June 20 into early July across the lower Midwest and Deep South combined particles from vehicles, power plants, and fires under stable humid conditions.
A retained source supports the attributed cause for the stated place and dates.
The regional account does not quantify source shares in Little Rock.
NASA Earth Observatory
NASA describes particle pollution across the Mississippi River Valley and Deep South from June 20 onward, with stable humid air trapping aerosol from vehicles, power plants, and fires; its June 23 satellite image shows the haze over the lower Midwest and Gulf region.
A retained source supports the attributed cause for the stated place and dates.
The source mixture is regional and not apportioned by metro.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
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.