Stagnant pollution mixture Possible
Daily PM2.5 peaked at 49.9 µg/m³ near Baltimore across 1 covered metro home to 2.9 million people.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 1.8 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 5.1 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
A coherent 11-monitor Baltimore PM2.5 increase coincided with higher PM10, carbon monoxide, nitrogen dioxide, and ozone; sustained calm or light wind; pervasive haze; and an exact-date NWS ridge-and-cap pattern. The evidence supports a stagnant anthropogenic mixture at possible confidence. It does not establish a temperature inversion, regional PM transport, or the shares of individual emissions sources.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
National Weather Service surface observations via Iowa Environmental Mesonet · Aug 12, 2005 hypothesis
Baltimore-Washington International recorded 26 observations with a median wind speed of 3.5 knots. Thirteen observations were at or below three knots, 11 were calm, all 26 reported haze or mist, and visibility fell to two miles.
National Weather Service Baltimore/Washington Area Forecast Discussion via Iowa Environmental Mesonet · Aug 12, 2005 hypothesis
The exact-date NWS discussion described surface ridging along the Mid-Atlantic coast, broad ridging and a cap aloft that suppressed convection, light southerly flow, and haze expected to linger through the morning in high humidity.
U.S. EPA AirData hypothesis
EPA records show median daily PM2.5 of 48.5 micrograms per cubic meter across 11 federal-reference monitors. A colocated hourly series was 46.8 micrograms per cubic meter. PM10 was 52 micrograms per cubic meter, while carbon monoxide, nitrogen dioxide, and ozone were all at least 20 percent above their adjacent-window comparisons.
Inference, not direct attribution
official_surface_weak_dispersion_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
official_surface_weak_dispersion_multimonitor_accumulation.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 2.3 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.
Baltimore-Columbia-Towson, MD
Monitor comparison window 2005-08-09 to 2005-08-15 · PM2.5 target: FMC-Fairfield
40% above nearby days
108% higher than surrounding days
40% higher than surrounding days
108% higher than surrounding days
25% higher than surrounding days
42% higher than surrounding days
5% higher than surrounding days
38% 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 |
|---|---|---|---|---|
| Baltimore-Columbia-Towson, MD | 49.9 µg/m³ | 2.3 | Aug 12, 2005 | #25 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 surface observations via Iowa Environmental Mesonet
Baltimore-Washington International recorded 26 observations with a median wind speed of 3.5 knots. Thirteen observations were at or below three knots, 11 were calm, all 26 reported haze or mist, and visibility fell to two miles.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
One airport station cannot describe every neighborhood in the metro or establish the vertical atmospheric profile by itself.
National Weather Service Baltimore/Washington Area Forecast Discussion via Iowa Environmental Mesonet
The exact-date NWS discussion described surface ridging along the Mid-Atlantic coast, broad ridging and a cap aloft that suppressed convection, light southerly flow, and haze expected to linger through the morning in high humidity.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The forecast discussion documents poor-dispersion context but does not name the particle sources, measure PM2.5 composition, or explicitly diagnose a temperature inversion.
U.S. EPA AirData
EPA records show median daily PM2.5 of 48.5 micrograms per cubic meter across 11 federal-reference monitors. A colocated hourly series was 46.8 micrograms per cubic meter. PM10 was 52 micrograms per cubic meter, while carbon monoxide, nitrogen dioxide, and ozone were all at least 20 percent above their adjacent-window comparisons.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The joint response supports a broad accumulated fine-particle mixture but does not apportion chemical components or source sectors.
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.