Stagnant pollution mixture Possible
Daily PM2.5 peaked at 63 µg/m³ near Birmingham across 1 covered metro home to 1.2 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 ≈ 4.4 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 5.3 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
The exact-window NWS Birmingham discussion says air quality would worsen as the local air mass became stagnant under very light winds. Surface observations and the EPA pollution fingerprint independently confirm prolonged haze, weak flow, and elevated particles. No dominant exceptional source was identified.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
National Weather Service Birmingham via Iowa Environmental Mesonet · Sep 12, 2005 corroborates
NWS Birmingham said haze would increase and air quality would worsen on September 12-13 as the local air mass became more moist and stagnant with very light winds. The following discussion described continued haze and light winds.
U.S. EPA AirData hypothesis
Certified EPA observations show median event-window PM2.5 of 53.4 micrograms per cubic meter across ten monitors and PM10 of 85.3 across four monitors, both above the preceding and following comparison windows; sulfur dioxide was also elevated.
NOAA/NWS surface observations via Iowa Environmental Mesonet hypothesis
The Birmingham airport record contains 48 event hours: median wind was calm, 25 hours were calm, 33 were at or below 3 knots, and haze was coded during 20 hours.
Inference, not direct attribution
documented_stagnation_overlap_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
NWS Birmingham said haze would increase and air quality would worsen on September 12-13 as the local air mass became more moist and stagnant with very light winds. The following discussion described continued haze and light winds.
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 2.9 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.
Birmingham-Hoover, AL
Monitor comparison window 2005-09-09 to 2005-09-16 · PM2.5 target: North Birmingham
37% above nearby days
38% higher than surrounding days
37% higher than surrounding days
38% higher than surrounding days
About the same as surrounding days
76% higher than surrounding days
19% higher 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 |
|---|---|---|---|---|
| Birmingham-Hoover, AL | 63 µg/m³ | 5.6 | Sep 12, 2005 | #4 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 Birmingham via Iowa Environmental Mesonet
NWS Birmingham said haze would increase and air quality would worsen on September 12-13 as the local air mass became more moist and stagnant with very light winds. The following discussion described continued haze and light winds.
A retained source supports the attributed cause for the stated place and dates.
The discussion identifies the accumulation mechanism but not the particles' dominant emitting sources.
U.S. EPA AirData
Certified EPA observations show median event-window PM2.5 of 53.4 micrograms per cubic meter across ten monitors and PM10 of 85.3 across four monitors, both above the preceding and following comparison windows; sulfur dioxide was also elevated.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The fingerprint confirms a multi-pollutant episode but does not identify the dominant emissions source.
NOAA/NWS surface observations via Iowa Environmental Mesonet
The Birmingham airport record contains 48 event hours: median wind was calm, 25 hours were calm, 33 were at or below 3 knots, and haze was coded during 20 hours.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The airport observations corroborate the weak-flow haze setting but do not identify a source.
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.