Stagnant pollution mixture Possible
Daily PM2.5 peaked at 47 µg/m³ near Chattanooga across 1 covered metro home to 588,050 people.
Why we think this happened
The exact-date NWS discussion said haze would remain a factor because the low-level pressure gradient was weak. EPA observations show PM2.5 elevated across four monitors during a continuing multi-day episode. This supports weak-flow accumulation of an unidentified mixture, with no basis for naming a specific source.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
National Weather Service Morristown via Iowa Environmental Mesonet · Oct 24, 2000 corroborates
NWS Morristown said haze would remain a factor around Chattanooga because the low-level pressure gradient was weak.
U.S. EPA AirData hypothesis
EPA observations show event-day PM2.5 near 47 micrograms per cubic meter across four monitors during a continuing elevated-particle period.
Inference, not direct attribution
documented_ridge_weak_flow_multimonitor_accumulation.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
NWS Morristown said haze would remain a factor around Chattanooga because the low-level pressure gradient was weak.
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 2.1 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.
Chattanooga, TN-GA
Monitor comparison window 2000-10-21 to 2000-10-27 · PM2.5 target: Siskin
0% above nearby 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.
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| Chattanooga, TN-GA | 47 µg/m³ | 2.1 | Oct 24, 2000 | #14 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.
National Weather Service Morristown via Iowa Environmental Mesonet
NWS Morristown said haze would remain a factor around Chattanooga because the low-level pressure gradient was weak.
A retained source supports the attributed cause for the stated place and dates.
The discussion directly documents weak-flow haze but does not identify its emissions sources or quantify the PM2.5 contribution.
U.S. EPA AirData
EPA observations show event-day PM2.5 near 47 micrograms per cubic meter across four monitors during a continuing elevated-particle period.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
Available co-pollutant coverage is sparse, and the PM2.5 pattern cannot distinguish regional secondary aerosol, local combustion, or transported smoke.
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.