Stagnant pollution mixture Possible
Daily PM2.5 peaked at 76.7 µg/m³ near San Francisco across 1 covered metro home to 4.6 million people.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 3.0 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 14 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
NWS San Francisco documented a flat surface-pressure pattern, weakening offshore flow, boundary-layer saturation, and calm stable air on the exact event date. This supports stagnant accumulation as a possible mechanism for the Bay Area place-first child; the same evidence does not cover Sacramento, which remains unresolved.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
National Weather Service San Francisco Bay Area via Iowa Environmental Mesonet · Nov 30, 2002 hypothesis
NWS San Francisco reported weakening offshore flow, a flat surface-pressure pattern, increasing low-level moisture and boundary-layer saturation, and calm stable air conducive to inland valley fog.
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 3.5 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.
San Francisco-Oakland-Hayward, CA
Monitor comparison window 2002-11-27 to 2002-12-03 · PM2.5 target: Concord
73% above nearby days
11% lower than surrounding days
About the same as surrounding days
73% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
29% lower than surrounding days
About the same as surrounding days
About the same as surrounding days
11% 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.
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 |
|---|---|---|---|---|
| San Francisco-Oakland-Hayward, CA | 76.7 µg/m³ | 3.5 | Nov 30, 2002 | #22 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 San Francisco Bay Area via Iowa Environmental Mesonet
NWS San Francisco reported weakening offshore flow, a flat surface-pressure pattern, increasing low-level moisture and boundary-layer saturation, and calm stable air conducive to inland valley fog.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The discussion does not mention PM2.5 or identify the accumulated emissions mixture.
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.