Stagnant pollution mixture Possible
Daily PM2.5 peaked at 43 µg/m³ near Kansas City 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 ≈ 1.5 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 3.3 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 exact-date NWS discussion describes fog and stratus trapped under a surface ridge and persistent high pressure. EPA data show a broad PM2.5 rise across six daily monitoring series, higher PM10, and substantially weaker wind than before the event. This supports a trapped mixed-pollution mechanism without identifying a specific source.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
National Weather Service Kansas City via Iowa Environmental Mesonet · Jan 15, 2010 corroborates
NWS Kansas City described fog and stratus trapped under the high, difficult erosion, and surface ridging over the region during the January 15 event.
U.S. EPA AirData hypothesis
EPA observations show daily PM2.5 of 43 micrograms per cubic meter across six monitoring series, compared with medians of 19.5 before and 13 after; PM10 was also elevated and event-window wind was roughly half the preceding-window value.
Inference, not direct attribution
documented_ridge_weak_flow_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 Kansas City described fog and stratus trapped under the high, difficult erosion, and surface ridging over the region during the January 15 event.
View supporting source ↗Air-mass movement
NOAA HYSPLIT modeled 12 backward paths across multiple arrival times and heights. They show where the air traveled, not which source polluted it.
Explore the modeled paths ↓Local response
EPA monitors recorded the event across 1 metro. The peak daily concentration is roughly 2.0 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.
Kansas City, MO-KS
Monitor comparison window 2010-01-12 to 2010-01-18 · PM2.5 target: Troost
121% above nearby days
About the same as surrounding days
7% lower than surrounding days
121% higher than surrounding days
7% lower than surrounding days
6% higher than surrounding days
47% higher than surrounding days
23% lower than surrounding days
17% lower than 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.
Air-mass reconstruction
NOAA HYSPLIT traces the air arriving at each metro backward for 72 hours. Multiple arrival times and heights show whether the broad path is stable—or sensitive to assumptions about when and where the polluted layer arrived.
Air arriving near Kansas City
Peak-date arrivals · 2010-01-15
Each line begins 72 hours before arrival and points toward the metro. Color represents arrival height; repeated lines represent 00, 06, 12, and 18 UTC arrival assumptions. A path can show where the air traveled, but it cannot prove which source added the PM2.5.
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.
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| Kansas City, MO-KS | 43 µg/m³ | 2.0 | Jan 15, 2010 | #12 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 Kansas City via Iowa Environmental Mesonet
NWS Kansas City described fog and stratus trapped under the high, difficult erosion, and surface ridging over the region during the January 15 event.
A retained source supports the attributed cause for the stated place and dates.
The discussion establishes a trapping environment but does not identify the pollution source or explicitly discuss PM2.5.
U.S. EPA AirData
EPA observations show daily PM2.5 of 43 micrograms per cubic meter across six monitoring series, compared with medians of 19.5 before and 13 after; PM10 was also elevated and event-window wind was roughly half the preceding-window value.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The fingerprint supports regional accumulation but does not apportion the particulate mixture among 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.