Temperature inversion Possible
Daily PM2.5 peaked at 51.6 µg/m³ near Indianapolis across 1 covered metro home to 2.2 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 ≈ 3.8 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
Indianapolis's seven-monitor daily PM2.5 value rose with PM10, nitrogen dioxide, sulfur dioxide, and carbon monoxide. Exact-date NWS discussions reported morning haze and low-level moisture becoming trapped beneath a strong inversion. Together they support inversion trapping at possible confidence without identifying one emitting source.
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 a median daily PM2.5 value of 41.3 micrograms per cubic meter across 7 monitors during the event, compared with 23.4 before and 26.15 after. Same-window context included PM10 Total 0-10um STP 49 Micrograms/cubic meter (25 C), Carbon monoxide 0.5708 Parts per million, Nitrogen dioxide (NO2) 37.7 Parts per billion, Sulfur dioxide 9.7792 Parts per billion, Ozone 0.0281 Parts per million.
National Weather Service via Iowa Environmental Mesonet · Feb 13, 2014 hypothesis
NWS Indianapolis reported brief morning haze or fog and forecast low-level moisture becoming trapped beneath a strong inversion later in the event day.
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.
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 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 “Temperature inversion” explanation; it does not assign the cause by itself.
Indianapolis-Carmel-Anderson, IN
Monitor comparison window 2014-02-10 to 2014-02-16 · PM2.5 target: Anderson- Eastside Elem. School
58% above nearby days
3 calm hours observed
Haze reported during 2 hours
58% higher than surrounding days
69% higher than surrounding days
25% higher than surrounding days
77% higher than surrounding days
109% higher than surrounding days
About the same as surrounding days
10 kt maximum · 3 of 8 observed hours calm
0 observed hours at or below 3 miles
6.8°F to 32°F
78% 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 |
|---|---|---|---|---|
| Indianapolis-Carmel-Anderson, IN | 51.6 µg/m³ | 2.3 | Feb 13, 2014 | #21 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 via Iowa Environmental Mesonet
NWS Indianapolis reported brief morning haze or fog and forecast low-level moisture becoming trapped beneath a strong inversion later in the event day.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The inversion discussion was written partly in the context of moisture and freezing drizzle and does not apportion the measured particle mass.
U.S. EPA AirData
EPA records show a median daily PM2.5 value of 41.3 micrograms per cubic meter across 7 monitors during the event, compared with 23.4 before and 26.15 after. Same-window context included PM10 Total 0-10um STP 49 Micrograms/cubic meter (25 C), Carbon monoxide 0.5708 Parts per million, Nitrogen dioxide (NO2) 37.7 Parts per billion, Sulfur dioxide 9.7792 Parts per billion, Ozone 0.0281 Parts per million.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The measured fingerprint establishes the episode and co-pollutant pattern but cannot uniquely apportion its sources.
U.S. EPA EQUATES CMAQ via Remote Sensing Information Gateway
EPA's retrospective 12-kilometer model reproduced an event-centered fine-mass increase of 1.6952 times adjacent modeled days. The modeled mixture was 33.8% organic matter, 48.5% secondary ions, 4.6% soil, and 6.8% elemental carbon.
Context for the event; this item does not establish the attributed cause by itself.
EQUATES is a retrospective chemical-transport model, not a monitor observation or source-apportionment determination; it is retained as compatible composition context only.
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.