Stagnant pollution mixture Possible
Daily PM2.5 peaked at 75.2 µg/m³ near Birmingham across 1 covered metro home to 1.2 million people. 1 metro recorded their worst day on record.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 11.1 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 13 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
Exact Birmingham airport observations document a five-day haze episode dominated by calm or very light wind. Local peer-reviewed studies independently identify the October 25 peak and the recurring North Birmingham mixture of regional sulfate and nitrate plus local coal, vehicle, wood-smoke, and industrial factors. The sources support a trapped mixed-pollution mechanism, not an exact-day source allocation.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
Gupta and Christopher, Atmospheric Chemistry and Physics · Jun 27, 2008 hypothesis
The peer-reviewed North Birmingham analysis identifies October 25, 2000 as its seven-year maximum 24-hour PM2.5 day at 75.3 micrograms per cubic meter. It says daily variation is mainly associated with local meteorology and changing local emissions, while noting that transport can also contribute.
NOAA/NWS surface observations via Iowa Environmental Mesonet hypothesis
The Birmingham airport record contains 114 observed event hours: median wind was calm, 78 hours were calm, 87 were at or below 3 knots, and haze was coded during 66 hours. Median sea-level pressure was 1022.55 mb.
U.S. EPA AirData hypothesis
Certified EPA observations show a broad particle and combustion-pollutant episode: median event-window PM2.5 was 49.5 micrograms per cubic meter across eight monitors, PM10 was 111.5, and carbon monoxide and sulfur dioxide were also elevated relative to the preceding comparison window.
Inference, not direct attribution
local_seasonal_profile_with_exact_trapping_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_seasonal_profile_with_exact_trapping_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.
Birmingham-Hoover, AL
Monitor comparison window 2000-10-20 to 2000-10-30 · PM2.5 target: Wylam
23% above nearby days
39% higher than surrounding days
23% higher than surrounding days
39% higher than surrounding days
27% higher than surrounding days
50% higher than surrounding days
10% 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 | 75.2 µg/m³ | 14.1 | Oct 25, 2000 | Worst day on record |
"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.
NOAA/NWS surface observations via Iowa Environmental Mesonet
The Birmingham airport record contains 114 observed event hours: median wind was calm, 78 hours were calm, 87 were at or below 3 knots, and haze was coded during 66 hours. Median sea-level pressure was 1022.55 mb.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
One airport record describes the local trapping setting but cannot identify the particles' emitting sources or prove a temperature inversion.
U.S. EPA AirData
Certified EPA observations show a broad particle and combustion-pollutant episode: median event-window PM2.5 was 49.5 micrograms per cubic meter across eight monitors, PM10 was 111.5, and carbon monoxide and sulfur dioxide were also elevated relative to the preceding comparison window.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The multi-monitor fingerprint confirms a mixed pollution episode but does not apportion PM2.5 to individual sources; pollutants need not have been measured at the same site.
Gupta and Christopher, Atmospheric Chemistry and Physics
The peer-reviewed North Birmingham analysis identifies October 25, 2000 as its seven-year maximum 24-hour PM2.5 day at 75.3 micrograms per cubic meter. It says daily variation is mainly associated with local meteorology and changing local emissions, while noting that transport can also contribute.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The paper identifies the exact peak and broad controls but does not apportion that day's PM2.5 among sources.
Liu et al., Atmospheric Environment
Positive matrix factorization of North Birmingham observations from 2000-2002 resolved recurring regional sulfate, nitrate, and soil factors alongside local coal combustion, vehicle, wood-smoke, and industrial factors, with distinct seasonal behavior.
Context for the event; this item does not establish the attributed cause by itself.
This is a recurring local source profile, not an allocation of the October 23-27 event; no historical factor percentages are assigned to the event days.
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.