Temperature inversion Possible
Daily PM2.5 peaked at 59.7 µg/m³ near Indianapolis 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 ≈ 2.1 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 4.6 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
An exact-date NWS discussion forecast a very strong near-surface inversion under clear skies and calm wind. Indiana's official monitor table and EPA observations independently show a broad Indianapolis particle episode with elevated combustion tracers. The evidence supports an inversion-driven accumulation mechanism but does not identify a dominant emitting source.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
National Weather Service Indianapolis via Iowa Environmental Mesonet · Nov 1, 2022 corroborates
NWS Indianapolis expected a very strong near-surface inversion on November 1, with clear skies and calm winds combining to strengthen the overnight inversion.
wishtv.com · Nov 2, 2022 corroborates
Indiana Department of Environmental Management hypothesis
Indiana's official annual table lists elevated November 1 PM2.5 at multiple Indianapolis-area monitors, including 59.7 micrograms per cubic meter at Washington Park.
Inference, not direct attribution
documented_inversion_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
NWS Indianapolis expected a very strong near-surface inversion on November 1, with clear skies and calm winds combining to strengthen the overnight inversion.
View supporting source ↗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 2.7 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 “Temperature inversion” explanation; it does not assign the cause by itself.
Indianapolis-Carmel-Anderson, IN
Monitor comparison window 2022-10-29 to 2022-11-04 · PM2.5 target: Indpls- Washington Park/ in parking lot next to police station
83% above nearby days
14% higher than surrounding days
133% higher than surrounding days
83% higher than surrounding days
133% higher than surrounding days
55% higher than surrounding days
53% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
14% 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 |
|---|---|---|---|---|
| Indianapolis-Carmel-Anderson, IN | 59.7 µg/m³ | 2.7 | Nov 1, 2022 | #10 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 Indianapolis via Iowa Environmental Mesonet
NWS Indianapolis expected a very strong near-surface inversion on November 1, with clear skies and calm winds combining to strengthen the overnight inversion.
A retained source supports the attributed cause for the stated place and dates.
The forecast discussion identifies the trapping mechanism but not the particles' emitting sources.
Indiana Department of Environmental Management
Indiana's official annual table lists elevated November 1 PM2.5 at multiple Indianapolis-area monitors, including 59.7 micrograms per cubic meter at Washington Park.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The table confirms the date and monitored values but does not assign an emissions source.
U.S. EPA AirData
EPA observations show elevated PM2.5 across five hourly-series monitors and six daily-series monitors, accompanied by higher PM10, carbon monoxide, and nitrogen dioxide than 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 accumulation but cannot apportion PM2.5 among local or transported sources; pollutants need not have been measured at the same site.
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.