Stagnant pollution mixture Possible
Daily PM2.5 peaked at 53.2 µg/m³ near Cincinnati across 2 covered metros home to 3.1 million people.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 4.2 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-window NWS discussions described high pressure and an upper ridge holding over the Ohio Valley, then explicitly called the pattern hot, humid, and stagnant and reported heavy haze. Separate Cincinnati and Dayton monitor fingerprints show broad PM2.5 rises with compatible co-pollutants and weak surface wind. This supports stagnant mixed-pollution accumulation as a possible mechanism for Cincinnati and Dayton only; Columbus remains unresolved.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
National Weather Service Wilmington, Ohio via Iowa Environmental Mesonet · Aug 7, 2001 hypothesis
The exact-window NWS discussion said the upper ridge was allowing a hot, humid, stagnant pattern to continue; a later update reported heavy haze at the forecast office.
National Weather Service surface observations via Iowa Environmental Mesonet · Aug 6, 2001 hypothesis
Cincinnati's official station recorded 21 hours of haze; 76.1% of event hours had wind at or below three knots, 69% were calm, and visibility was restricted during 52.1% of hours.
U.S. EPA AirData · Aug 6, 2001 hypothesis
EPA records show median daily PM2.5 of 44.1 micrograms per cubic meter across three Dayton monitors, about 2.6 times the adjacent-window level, with compatible carbon monoxide and sulfur dioxide increases.
Inference, not direct attribution
Documented inversion overlap: The event overlaps a documented inversion period, but the retained material does not directly attribute the measured PM2.5 episode.
official_regional_stagnation_multimonitor_fingerprint.v1: This inference is recorded in the catalog methodology.
official_surface_weak_dispersion_multimonitor_accumulation.v1: This inference is recorded in the catalog methodology.
See every retained source and limitation ↓
Sequence: Cincinnati (Aug 6) → Dayton (Aug 8)
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
Documented inversion overlap. The event overlaps a documented inversion period, but the retained material does not directly attribute the measured PM2.5 episode.
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 2.4 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.
Cincinnati, OH-KY-IN
Monitor comparison window 2001-08-03 to 2001-08-11 · PM2.5 target: NORWOOD
76% above nearby days
74% higher than surrounding days
76% higher than surrounding days
74% higher than surrounding days
42% higher than surrounding days
34% higher than surrounding days
53% higher than surrounding days
14% higher than surrounding days
6% higher than surrounding days
Columbus, OH
Monitor comparison window 2001-08-03 to 2001-08-11 · PM2.5 target: ANN ST.
67% above nearby days
22 calm hours observed
Haze reported during 28 hours
67% higher than surrounding days
88% higher than surrounding days
23% higher than surrounding days
65% higher than surrounding days
About the same as surrounding days
11 kt maximum · 22 of 72 observed hours calm
8 observed hours at or below 3 miles
68°F to 92°F
94% maximum
Dayton, OH
Monitor comparison window 2001-08-03 to 2001-08-11 · PM2.5 target: LIBRARY (DAYTON PUBLIC
110% above nearby days
28% higher than surrounding days
110% higher than surrounding days
28% higher than surrounding days
33% higher than surrounding days
7% higher than surrounding days
Indianapolis-Carmel-Anderson, IN
Monitor comparison window 2001-08-03 to 2001-08-11 · PM2.5 target: Indpls- West St.
169% above nearby days
48% higher than surrounding days
169% higher than surrounding days
48% higher than surrounding days
60% higher than surrounding days
46% higher than surrounding days
22% higher than surrounding days
5% lower than surrounding 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.
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 |
|---|---|---|---|---|
| Cincinnati, OH-KY-IN | 53.2 µg/m³ | 6.9 | Aug 7, 2001 | #11 of its top days |
| Dayton, OH | 47.8 µg/m³ | 2.2 | Aug 8, 2001 | #15 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
Across 72 observed event hours, Columbus airport reported a median wind of four knots, 22 calm hours, 28 haze-coded hours, eight hours with visibility at or below three miles, and minimum visibility of 1.25 miles.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
One airport documents surface ventilation and obscuration but not the full metropolitan mixing layer.
National Weather Service Wilmington, Ohio via Iowa Environmental Mesonet
The exact-window NWS discussion said the upper ridge was allowing a hot, humid, stagnant pattern to continue; a later update reported heavy haze at the forecast office.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The discussion covers the Wilmington forecast region, including central and southwest Ohio, but does not identify the chemical source mixture.
National Weather Service surface observations via Iowa Environmental Mesonet
Cincinnati's official station recorded 21 hours of haze; 76.1% of event hours had wind at or below three knots, 69% were calm, and visibility was restricted during 52.1% of hours.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
One airport station cannot fully characterize metro-wide ventilation, and haze is not source-specific.
U.S. EPA AirData
EPA records show median daily PM2.5 of 44.1 micrograms per cubic meter across three Dayton monitors, about 2.6 times the adjacent-window level, with compatible carbon monoxide and sulfur dioxide increases.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The fingerprint supports mixed accumulation but cannot apportion source sectors.
National Weather Service surface observations via Iowa Environmental Mesonet
Dayton's official station recorded 33 hours of haze; 56.5% of event hours had wind at or below three knots and visibility was restricted during 10.1% of hours.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
One airport station cannot fully characterize metro-wide ventilation, and haze is not source-specific.
U.S. EPA AirData
EPA records show median daily PM2.5 of 46.4 micrograms per cubic meter across 12 Cincinnati monitors, more than twice the adjacent-window level, with compatible PM10, carbon monoxide, nitrogen dioxide, and sulfur dioxide increases.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The fingerprint supports mixed accumulation but cannot apportion source sectors.
National Weather Service Indianapolis via Iowa Environmental Mesonet
The NWS said a subsidence inversion shown in forecast soundings would persist for several days, with air trapped beneath it heating and moistening during the supplied event window.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The discussion supports Indianapolis only, not Cincinnati, Columbus, or Dayton.
U.S. EPA AirData
EPA records show median daily PM2.5 of 38 micrograms per cubic meter across three Columbus monitors, 1.67 times the adjacent-window level. PM10 rose to 62 micrograms per cubic meter, while carbon monoxide and sulfur dioxide also increased relative to the adjacent window.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The pollution fingerprint is descriptive and cannot uniquely apportion traffic, power generation, industry, secondary aerosol, or other sources.
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.