Stagnant pollution mixture Possible
Daily PM2.5 peaked at 38.5 µg/m³ near Tulsa across 1 covered metro home to 1.1 million people.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 2.5 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 2.7 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
Tulsa's two-day PM2.5 episode occurred while exact-window NWS discussions described a largely stagnant local pattern, building upper-level high pressure, and haze that persisted for several days before stronger flow dispersed it. This supports broad stagnant mixed-pollution accumulation at possible confidence; no single source sector is assigned.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
National Weather Service via Iowa Environmental Mesonet · Aug 3, 2007 hypothesis
NWS Tulsa added haze to the local forecast on the second event day; the following discussion said haze had persisted for several days and stronger southerly flow would help disperse it.
U.S. EPA AirData hypothesis
EPA records show a median daily PM2.5 value of 36.05 micrograms per cubic meter across 2 monitors during the event, compared with 21.65 before and 18 after. Same-window context included PM10 Total 0-10um STP null Micrograms/cubic meter (25 C), Carbon monoxide 0.6633 Parts per million, Nitrogen dioxide (NO2) 12.2645 Parts per billion, Sulfur dioxide 1.411 Parts per billion, Ozone 0.0395 Parts per million.
National Weather Service via Iowa Environmental Mesonet · Aug 2, 2007 hypothesis
NWS Tulsa described the overall pattern as largely stagnant across its forecast area on the first event morning, with an upper ridge building over the area.
Inference, not direct attribution
documented_stagnation_overlap_possible.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
documented_stagnation_overlap_possible.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 1.8 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.
Tulsa, OK
Monitor comparison window 2007-07-30 to 2007-08-06 · PM2.5 target: TCCHD (OLD)
70% above nearby days
17 calm hours observed
Haze reported during 18 hours
70% higher than surrounding days
42% higher than surrounding days
30% higher than surrounding days
About the same as surrounding days
7% higher than surrounding days
11 kt maximum · 17 of 48 observed hours calm
7 observed hours at or below 3 miles
72°F to 93°F
91% 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.
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| Tulsa, OK | 38.5 µg/m³ | 3.4 | Aug 3, 2007 | #11 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 Tulsa added haze to the local forecast on the second event day; the following discussion said haze had persisted for several days and stronger southerly flow would help disperse it.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
Haze is not source-specific and can include particles from multiple local and transported sources.
National Weather Service via Iowa Environmental Mesonet
NWS Tulsa described the overall pattern as largely stagnant across its forecast area on the first event morning, with an upper ridge building over the area.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The discussion documents the accumulation setting but does not identify the particle 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 1.6161 times adjacent modeled days. The modeled mixture was 56.2% organic matter, 36.2% secondary ions, 4.1% soil, and 1.3% 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.
U.S. EPA AirData
EPA records show a median daily PM2.5 value of 36.05 micrograms per cubic meter across 2 monitors during the event, compared with 21.65 before and 18 after. Same-window context included PM10 Total 0-10um STP null Micrograms/cubic meter (25 C), Carbon monoxide 0.6633 Parts per million, Nitrogen dioxide (NO2) 12.2645 Parts per billion, Sulfur dioxide 1.411 Parts per billion, Ozone 0.0395 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.
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.