National Weather Service Wilmington, Ohio via Iowa Environmental Mesonet · Jul 20, 2001 hypothesis
Area Forecast Discussion: stagnant air mass
The same-day NWS discussion described a stagnant air mass over the Columbus forecast area.
Stagnant pollution mixture Possible
2001-07-20 Columbus, OH stagnant mixed-pollution episode
Daily PM2.5 peaked at 60.2 µg/m³ near Columbus across 1 covered metro home to 2.2 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 ≈ 2.3 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 5.0 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 basis for “Stagnant pollution mixture”
The same-day NWS discussion described a stagnant air mass over the Columbus forecast area. The retained scope and limitations support possible confidence for this local episode.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
Evidence path
From source to city
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.
- 1Open question
Source or mechanism
Source not directly documented
The catalog has a grouping hypothesis, but no retained source directly establishes the proposed cause.
- 2Research gap
Air-mass movement
The transport path has not been reconstructed
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.
- 3Documented
Local response
60.2 µg/m³ near Columbus
EPA monitors recorded the event across 1 metro. The peak daily concentration is roughly 2.7 cigarette-equivalents at the outdoor daily rate.
Inspect the pollutant and weather signals ↓
Event autopsy
What the instruments saw
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.
Columbus, OH
Monitor comparison window 2001-07-17 to 2001-07-23 · PM2.5 target: Fairgrounds Garage
81% above nearby days
73% higher than surrounding days
Pollution fingerprint
Metro-wide median of reporting monitors PM2.5 60 µg/m³
81% higher than surrounding days
Before25.6 µg/m³ Event60 µg/m³ After34.4 µg/m³
PM10 76 µg/m³
73% higher than surrounding days
Before40 µg/m³ Event76 µg/m³ After44 µg/m³
Carbon monoxide 0.531 ppm
32% higher than surrounding days
Before0.535 ppm Event0.531 ppm After0.348 ppm
Sulfur dioxide 3.05 ppb
150% higher than surrounding days
Before0.565 ppb Event3.05 ppb After1.43 ppb
Ozone 0.055 ppm
10% higher than surrounding days
Before0.039 ppm Event0.055 ppm After0.050 ppm
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.
Measured daily PM2.5 at EPA monitors, as cigarette-equivalents
EPA monitors sit in metro areas, so the colour clusters there. Land between and beyond
them is unmeasured, not clean: this map shows where IAQng has readings, not the extent
of the smoke.
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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
Camera views near
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.
Affected metros
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| Columbus, OH | 60.2 µg/m³ | 2.7 | Jul 20, 2001 | #8 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
What supports this account
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.
Area Forecast Discussion: stagnant air mass
National Weather Service Wilmington, Ohio via Iowa Environmental Mesonet
The same-day NWS discussion described a stagnant air mass over the Columbus forecast area.
What it supports
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
Limit
Stagnation supports accumulation of the measured pollution but does not identify its source mixture.
What remains uncertain
- Stagnation supports accumulation of the measured pollution but does not identify its source mixture.
Status and provenance
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.