U.S. EPA AirData / Chemical Speciation Network hypothesis
EPA AirData daily_SPEC 2001
Exact-peak-date CSN composition estimated a 36.8% secondary-inorganic share of reconstructed PM2.5 mass at the covered bakersfield monitor set.
Stagnant pollution mixture Possible
2001-01-22 Bakersfield, CA stagnant mixed-pollution episode
Daily PM2.5 peaked at 120.4 µg/m³ near Bakersfield across 1 covered metro home to 922,529 people. 1 metro placed a top-ten day in their record.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 4.9 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 4.5 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 “Stagnant pollution mixture”
California's PM2.5 plan places January 22 inside the measured Bakersfield November 2000-February 2001 episode and attributes that winter's accumulation to persistent high pressure, light-to-calm winds, low mixing, and stable stagnation. Exact-date CSN composition shows a substantial but non-majority secondary-inorganic share, consistent with a mixed aerosol rather than one exceptional source.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
California Air Resources Board · Dec 20, 2012 hypothesis
2012 PM2.5 Plan Appendix B: Scientific Foundation
CARB's plan plots Bakersfield PM2.5 through the November 2000-February 2001 episode and says that winter was characterized by persistent high pressure, light-to-calm winds, low mixing, and stable stagnation. Its CRPAQS summary reports ammonium nitrate and biomass burning as the largest winter mixture components.
Inference, not direct attribution
documented_same_season_particle_episode_mixed_accumulation_possible.v1: This inference is recorded in the catalog methodology.
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
documented_same_season_particle_episode_mixed_accumulation_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
120.4 µg/m³ near Bakersfield
EPA monitors recorded the event across 1 metro. The peak daily concentration is roughly 5.5 cigarette-equivalents at the outdoor daily rate.
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 “Stagnant pollution mixture” explanation; it does not assign the cause by itself.
Bakersfield, CA
Monitor comparison window 2001-01-19 to 2001-01-25 · PM2.5 target: Bakersfield-Golden / M St
50% above nearby days
About the same as surrounding days
40% higher than surrounding days
Pollution fingerprint
Metro-wide median of reporting monitors PM2.5 110 µg/m³
50% higher than surrounding days
Before78.9 µg/m³ Event110 µg/m³ After34.5 µg/m³
PM10 127 µg/m³
40% higher than surrounding days
Before91 µg/m³ Event127 µg/m³ After11 µg/m³
Carbon monoxide 1.38 ppm
31% higher than surrounding days
Before1.01 ppm Event1.38 ppm After1.06 ppm
Nitrogen dioxide 20 ppb
21% higher than surrounding days
Before16.5 ppb Event20 ppb After11.7 ppb
Sulfur dioxide 2.26 ppb
About the same as surrounding days
Before2.52 ppb Event2.26 ppb After1.43 ppb
Ozone 0.021 ppm
6% lower than surrounding days
Before0.016 ppm Event0.021 ppm After0.025 ppm
Atmospheric conditions
Nearby EPA weather observationsAbout the same as surrounding days
About the same as surrounding days
About the same as 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.
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.
Affected metros
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| Bakersfield, CA | 120.4 µg/m³ | 5.5 | Jan 22, 2001 | #8 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.
2012 PM2.5 Plan Appendix B: Scientific Foundation
California Air Resources Board
CARB's plan plots Bakersfield PM2.5 through the November 2000-February 2001 episode and says that winter was characterized by persistent high pressure, light-to-calm winds, low mixing, and stable stagnation. Its CRPAQS summary reports ammonium nitrate and biomass burning as the largest winter mixture components.
What it supports
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
Limit
The meteorological conclusion applies to the measured winter episode, while the source-apportionment percentages are multi-site or intensive-period averages rather than an exact January 22 allocation.
EPA AirData daily_SPEC 2001
U.S. EPA AirData / Chemical Speciation Network
Exact-peak-date CSN composition estimated a 36.8% secondary-inorganic share of reconstructed PM2.5 mass at the covered bakersfield monitor set.
What it supports
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
Limit
Composition supports an aerosol mechanism, not an emitting source or named episode.
What remains uncertain
- The classification is a mechanism-level estimate capped at possible; it does not identify a unique source occurrence.
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.