Stagnant pollution mixture Possible
Daily PM2.5 peaked at 50.6 µg/m³ near Cincinnati across 1 covered metro home to 2.3 million people.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 1.7 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 3.9 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
Thirteen monitors show a sharp PM2.5 rise accompanied by higher PM10, carbon monoxide, and sulfur dioxide. The airport recorded calm or light wind during two-thirds of the day, with haze, mist, and restricted visibility, while the NWS placed the Ohio Valley under building surface and upper ridges. The evidence supports stagnant accumulation of a mixed plume as a possible broad mechanism.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
U.S. EPA AirData hypothesis
EPA records show median daily PM2.5 of 48.3 micrograms per cubic meter across 13 monitors, 2.159 times the adjacent-window level. Co-pollutants at least 10% above the adjacent-window comparison were pm10 (1.514x), carbon monoxide (1.207x), sulfur dioxide (1.366x). Other measured comparisons were nitrogen dioxide (0.852x).
National Weather Service Wilmington via Iowa Environmental Mesonet · Jun 29, 2002 hypothesis
The NWS discussion covering June 30 placed a surface high-pressure ridge through the Ohio Valley and said an upper ridge was building and would remain in place, with very little synoptic lift.
National Weather Service surface observations via Iowa Environmental Mesonet · Jun 30, 2002 hypothesis
CINCINNAT/LUNKEN recorded calm conditions during 63% of observed event hours and wind at or below three knots during 67%. The station recorded 6 haze hours, 12 mist hours, minimum visibility of 1 miles.
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.
Cincinnati, OH-KY-IN
Monitor comparison window 2002-06-27 to 2002-07-03 · PM2.5 target: Carthage
68% above nearby days
15 calm hours observed
Haze reported during 6 hours
68% higher than surrounding days
8% higher than surrounding days
6% higher than surrounding days
About the same as surrounding days
73% higher than surrounding days
28% higher than surrounding days
6 kt maximum · 15 of 24 observed hours calm
9 observed hours at or below 3 miles
66°F to 89°F
100% maximum
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 | 50.6 µg/m³ | 2.3 | Jun 30, 2002 | #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
CINCINNAT/LUNKEN recorded calm conditions during 63% of observed event hours and wind at or below three knots during 67%. The station recorded 6 haze hours, 12 mist hours, minimum visibility of 1 miles.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
A single surface station documents poor dispersion and obscuration but does not directly measure the vertical temperature profile or identify particle sources.
National Weather Service Wilmington via Iowa Environmental Mesonet
The NWS discussion covering June 30 placed a surface high-pressure ridge through the Ohio Valley and said an upper ridge was building and would remain in place, with very little synoptic lift.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The discussion establishes the regional setting but does not attribute the measured particles or identify source-sector shares.
U.S. Public Health Service air-pollution program via EPA NEPIS
The Cincinnati monitoring study explains that calm anticyclonic conditions and shallow or inverted mixing layers can severely suppress horizontal and vertical dilution, allowing local and regional pollutants to accumulate.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The report establishes a local atmospheric mechanism but predates and does not assess the June 30, 2002 episode.
U.S. EPA AirData
EPA records show median daily PM2.5 of 48.3 micrograms per cubic meter across 13 monitors, 2.159 times the adjacent-window level. Co-pollutants at least 10% above the adjacent-window comparison were pm10 (1.514x), carbon monoxide (1.207x), sulfur dioxide (1.366x). Other measured comparisons were nitrogen dioxide (0.852x).
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The multi-pollutant fingerprint demonstrates a broad accumulation episode but cannot apportion local combustion, industry, traffic, or secondary aerosol.
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.