Stagnant pollution mixture Possible
Daily PM2.5 peaked at 73.9 µg/m³ near Knoxville across 1 covered metro home to 957,608 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 ≈ 2.8 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 2.7 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
Five Knoxville-area PM2.5 monitors rose together, with compatible PM10, carbon monoxide, and sulfur dioxide increases. Exact-date Knoxville observations recorded haze, calm or very light wind, and strengthening high pressure. The nearest date-covered regional upper-air profile measured a strong 6.2-degree-Celsius inversion in the first 203 meters that morning. Together these observations support stagnant anthropogenic mixture at possible confidence; the regional sounding distance and absence of exact-day chemical speciation prevent a stronger or source-specific claim.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
U.S. EPA AirData · Jun 11, 2001 hypothesis
EPA records show median daily PM2.5 of 52.55 micrograms per cubic meter across five monitors, about twice the adjacent-window level, with compatible increases in PM10, carbon monoxide, and sulfur dioxide.
National Weather Service Morristown via Iowa Environmental Mesonet · Jun 11, 2001 hypothesis
The exact-date NWS discussion said the surface and upper ridge would strengthen across the Southeast and that high pressure remained over the area.
National Weather Service surface observations via Iowa Environmental Mesonet · Jun 11, 2001 hypothesis
Knoxville's official surface station recorded six hours of haze; 54.2% of event hours had wind at or below three knots and 37.5% were calm.
Inference, not direct attribution
local_stagnation_plus_regional_measured_inversion_possible.v1: This inference is recorded in the catalog methodology.
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
local_stagnation_plus_regional_measured_inversion_possible.v1. This inference is recorded in the catalog methodology.
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 3.4 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 “Stagnant pollution mixture” explanation; it does not assign the cause by itself.
Knoxville, TN
Monitor comparison window 2001-06-08 to 2001-06-14 · PM2.5 target: Spring Hill Elementary School
104% above nearby days
20% lower than surrounding days
32% higher than surrounding days
104% higher than surrounding days
32% higher than surrounding days
39% higher than surrounding days
178% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
20% 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 |
|---|---|---|---|---|
| Knoxville, TN | 73.9 µg/m³ | 3.4 | Jun 11, 2001 | #5 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. EPA AirData
EPA records show median daily PM2.5 of 52.55 micrograms per cubic meter across five monitors, about twice the adjacent-window level, with compatible increases in PM10, carbon monoxide, and sulfur dioxide.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The fingerprint supports mixed accumulation but cannot identify a unique source or distinguish local from regional contributions.
National Weather Service Morristown via Iowa Environmental Mesonet
The exact-date NWS discussion said the surface and upper ridge would strengthen across the Southeast and that high pressure remained over the area.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The discussion establishes a stagnant synoptic setting but does not attribute the PM2.5 episode to a particular source.
NOAA IGRA / University of Wyoming upper-air archive
The nearest date-covered upper-air station, Nashville (218 kilometers from the Knoxville analysis point), measured a strong morning surface inversion at 12 UTC: temperature rose 6.2 degrees Celsius from 180 to 383 meters elevation, a 203-meter layer.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The sounding is regional evidence from Nashville, not a direct measurement of Knoxville's complex-terrain boundary layer.
National Weather Service surface observations via Iowa Environmental Mesonet
Knoxville's official surface station recorded six hours of haze; 54.2% of event hours had wind at or below three knots and 37.5% were calm.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
One airport station cannot fully characterize metro-wide ventilation, and haze is not source-specific.
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.