Stagnant pollution mixture Possible
Daily PM2.5 peaked at 48.2 µg/m³ near Jackson across 2 covered metros home to 1.5 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 ≈ 2.3 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 3.4 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 2 source events to one stagnant mixed-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 / Federal Register · Jan 30, 2004 official
EPA describes a large-scale September 8-14 haze event spreading through the Southcentral and Southeastern United States; on September 11-12 the Midwest plume mixed with additional pollutants from Texas and the Southeast.
See every retained source and limitation ↓
Sequence: Jackson (Sep 11) → Baton Rouge (Sep 11)
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 a large-scale September 8-14 haze event spreading through the Southcentral and Southeastern United States; on September 11-12 the Midwest plume mixed with additional pollutants from Texas and the Southeast.
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 2 metros. The peak daily concentration is roughly 2.2 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.
Jackson, MS
Monitor comparison window 2002-09-08 to 2002-09-14 · PM2.5 target: RANKIN CO HEALTH DEPARTMENT-ROOF
171% above nearby days
77% higher than surrounding days
171% higher than surrounding days
77% higher than surrounding days
142% higher than surrounding days
66% higher than surrounding days
Baton Rouge, LA
Monitor comparison window 2002-09-08 to 2002-09-15 · PM2.5 target: Capitol
98% above nearby days
10% lower than surrounding days
No adjacent-day comparison
98% higher than surrounding days
No adjacent-day comparison
13% higher than surrounding days
31% higher than surrounding days
16% lower than surrounding days
63% higher than surrounding days
7% lower than surrounding days
About the same as surrounding days
About the same as surrounding days
10% 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.
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| Jackson, MS | 48.2 µg/m³ | 2.2 | Sep 11, 2002 | #2 of its top days |
| Baton Rouge, LA | 41.2 µg/m³ | 3.6 | Sep 12, 2002 | #19 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 a large-scale September 8-14 haze event spreading through the Southcentral and Southeastern United States; on September 11-12 the Midwest plume mixed with additional pollutants from Texas and the Southeast.
An official source supports the attributed cause for the stated place and dates.
The narrative covers Baton Rouge's region and date but does not apportion the city's daily PM2.5 mass.
U.S. Environmental Protection Agency / Federal Register
EPA describes a large-scale September 8-14 haze event that formed over the lower Ohio Valley and spread through the Southcentral and Southeastern United States; on September 11-12 the Midwest plume mixed with additional pollutants from Texas and the Southeast.
An official source supports the attributed cause for the stated place and dates.
The narrative covers Jackson's region and date but does not apportion the city's daily PM2.5 mass.
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.