Temperature inversion Possible
Daily PM2.5 peaked at 82.8 µg/m³ near Los Angeles across 1 covered metro home to 13 million people.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 3.1 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 40 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
A broad 11-monitor PM2.5 episode with elevated CO and NO2 occurred beneath an exceptionally strong, shallow inversion documented by NWS on the exact date, with haze and inhibited clearing. This supports trapped urban and regional pollution under a temperature inversion. A same-day refinery flare is retained as a possible contributor only: the record lacks plume evidence and daily SO2 did not rise with the regional response.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
National Weather Service Los Angeles/Oxnard via Iowa Environmental Mesonet · Nov 19, 2007 hypothesis
The exact-date NWS Los Angeles/Oxnard discussion measured a 1,000-foot marine layer capped by an 11-degree inversion over 2,000 feet, with the first 9 degrees occurring in only 600 feet. It said the strong inversion would hinder clearing and reported local afternoon visibility reductions in haze.
U.S. EPA AirData hypothesis
IAQng's reproducible aggregation of EPA records found a broad Los Angeles episode across 11 PM2.5 monitors, with an event-day median of 67.9 ug/m3. CO and NO2 were elevated while ozone was suppressed; daily SO2 did not show a corresponding increase.
Inference, not direct attribution
documented_strong_inversion_multimonitor.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_strong_inversion_multimonitor.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 3.8 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 “Temperature inversion” explanation; it does not assign the cause by itself.
Los Angeles-Long Beach-Anaheim, CA
Monitor comparison window 2007-11-16 to 2007-11-22 · PM2.5 target: Long Beach (North)
75% above nearby days
7% lower than surrounding days
About the same as surrounding days
75% higher than surrounding days
About the same as surrounding days
83% higher than surrounding days
57% higher than surrounding days
About the same as surrounding days
53% lower than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
7% lower 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.
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| Los Angeles-Long Beach-Anaheim, CA | 82.8 µg/m³ | 3.8 | Nov 19, 2007 | #19 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.
U.S. Coast Guard National Response Center
NRC report 856162 records a same-day Paramount Petroleum flare after a sulfur-recovery-unit upset, with 512 pounds of sulfur dioxide reported released to air.
Context for the event; this item does not establish the attributed cause by itself.
The report documents a contemporaneous industrial release, not that it caused the metro-wide PM2.5 episode.
National Weather Service Los Angeles/Oxnard via Iowa Environmental Mesonet
The exact-date NWS Los Angeles/Oxnard discussion measured a 1,000-foot marine layer capped by an 11-degree inversion over 2,000 feet, with the first 9 degrees occurring in only 600 feet. It said the strong inversion would hinder clearing and reported local afternoon visibility reductions in haze.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The discussion establishes a strong trapping layer and observed haze, not the source-sector mix beneath the inversion.
U.S. EPA AirData
IAQng's reproducible aggregation of EPA records found a broad Los Angeles episode across 11 PM2.5 monitors, with an event-day median of 67.9 ug/m3. CO and NO2 were elevated while ozone was suppressed; daily SO2 did not show a corresponding increase.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The pollution fingerprint supports a broad combustion-pollution episode but does not apportion 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.