Bay Area Air Quality Management District · Dec 25, 2006 official
Advisory
The Bay Area Air Quality Management District issued a Spare the Air advisory dated December 25, 2006, contemporaneous with the San Francisco and San Jose event.
Residential combustion Possible
2006-12-25 San Francisco-Oakland-Hayward, CA and San Jose-Sunnyvale-Santa Clara, CA residential-combustion pollution episode
Daily PM2.5 peaked at 75.3 µg/m³ near San Francisco across 2 covered metros home to 6.6 million people.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 2.8 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 19 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 basis for “Residential combustion”
The exact day is a documented Bay Area PM2.5 outlier, while the regional air district and contemporaneous reporting identify residential wood burning as a major winter particle source. Christmas timing strengthens the estimate, but no exact-day source apportionment was recovered, so confidence remains possible.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
California Energy Commission filing hypothesis
Bay Area air-quality modeling report
The modeling record identifies Christmas Day 2006 as a conspicuous Bay Area PM2.5 outlier.
Inference, not direct attribution
holiday_residential_combustion_possible.v1: This inference is recorded in the catalog methodology.
See every retained source and limitation ↓
Sequence: San Francisco (Dec 25) → San Jose (Dec 25)
Evidence path
From source to city
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.
- 1Inferred
Source or mechanism
Pattern-based explanation
holiday_residential_combustion_possible.v1. This inference is recorded in the catalog methodology.
- 2Research gap
Air-mass movement
The transport path has not been reconstructed
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.
- 3Documented
Local response
75.3 µg/m³ near San Francisco
The Bay Area Air Quality Management District issued a Spare the Air advisory dated December 25, 2006, contemporaneous with the San Francisco and San Jose event.
Inspect the pollutant and weather signals ↓
Event autopsy
What the instruments saw
Before, during, and after the episode: nearby pollutant monitors and surface-weather stations show what changed. This context tests the “Residential combustion” explanation; it does not assign the cause by itself.
San Francisco-Oakland-Hayward, CA
Monitor comparison window 2006-12-22 to 2006-12-28 · PM2.5 target: Redwood City
232% above nearby days
15% lower than surrounding days
58% higher than surrounding days
Pollution fingerprint
Metro-wide median of reporting monitors PM2.5 57.2 µg/m³
232% higher than surrounding days
Before22.8 µg/m³ Event57.2 µg/m³ After6.50 µg/m³
PM10 57 µg/m³
58% higher than surrounding days
Before— Event57 µg/m³ After15 µg/m³
Carbon monoxide 0.796 ppm
34% higher than surrounding days
Before0.617 ppm Event0.796 ppm After0.356 ppm
Nitrogen dioxide 17.1 ppb
11% higher than surrounding days
Before16 ppb Event17.1 ppb After8.74 ppb
Sulfur dioxide 1.58 ppb
About the same as surrounding days
Before1.75 ppb Event1.58 ppb After0.409 ppb
Ozone 0.002 ppm
75% lower than surrounding days
Before0.005 ppm Event0.002 ppm After0.027 ppm
Atmospheric conditions
Nearby EPA weather observations7% lower than surrounding days
10% higher than surrounding days
15% lower than surrounding days
San Jose-Sunnyvale-Santa Clara, CA
Monitor comparison window 2006-12-22 to 2006-12-28 · PM2.5 target: San Jose - Jackson
197% above nearby days
No adjacent-day comparison
Pollution fingerprint
Metro-wide median of reporting monitors PM2.5 64.4 µg/m³
197% higher than surrounding days
Before21.7 µg/m³ Event64.4 µg/m³ After5.50 µg/m³
PM10 57 µg/m³
No adjacent-day comparison
Before— Event57 µg/m³ After—
Carbon monoxide 1.39 ppm
105% higher than surrounding days
Before0.986 ppm Event1.39 ppm After0.109 ppm
Nitrogen dioxide 28.9 ppb
29% higher than surrounding days
Before26.8 ppb Event28.9 ppb After13.5 ppb
Ozone 0.015 ppm
About the same as surrounding days
Before0.013 ppm Event0.015 ppm After0.028 ppm
Atmospheric conditions
Nearby EPA weather observations7% higher than surrounding days
6% higher 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.
Measured daily PM2.5 at EPA monitors, as cigarette-equivalents
EPA monitors sit in metro areas, so the colour clusters there. Land between and beyond
them is unmeasured, not clean: this map shows where IAQng has readings, not the extent
of the smoke.
—
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
Camera views near
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.
Affected metros
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| San Francisco-Oakland-Hayward, CA | 75.3 µg/m³ | 3.4 | Dec 25, 2006 | #25 of its top days |
| San Jose-Sunnyvale-Santa Clara, CA | 64.4 µg/m³ | 2.9 | Dec 25, 2006 | #23 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
What supports this account
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.
Air Currents, Winter 2006
Bay Area Air Quality Management District
The regional air district's winter 2006 publication identifies fireplaces, wood stoves, and vehicle traffic as major winter PM2.5 sources and urges residents to limit wood burning.
What it supports
Context for the event; this item does not establish the attributed cause by itself.
Limit
The publication establishes the regional source pattern but does not quantify Christmas Day emissions.
Historical particulate matter data
Bay Area Air Quality Management District
The regional air district documents recurring winter PM2.5 episodes and Spare the Air alerts in the Bay Area.
What it supports
Context for the event; this item does not establish the attributed cause by itself.
Limit
The page does not attribute December 25, 2006 or isolate wood burning from other sources.
Bay Area air-quality modeling report
California Energy Commission filing
The modeling record identifies Christmas Day 2006 as a conspicuous Bay Area PM2.5 outlier.
What it supports
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
Limit
The accessible passage identifies the outlier but does not assign its source.
Spare the air tonight in Bay Area
SFGate
Contemporaneous Bay Area reporting identified wood burning and motor vehicles as the principal winter particle sources during the same month.
What it supports
Context for the event; this item does not establish the attributed cause by itself.
Limit
The story is from December 1, not Christmas Day, and describes the regional winter source profile rather than exact-day apportionment.
What remains uncertain
- The estimate cannot isolate residential combustion from traffic and other trapped winter emissions.
Status and provenance
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.