2002-10-14 Riverside-San Bernardino-Ontario, CA stagnant mixed-pollution episode
October 14, 2002
Daily PM2.5 peaked at 82.1 µg/m³ near Riverside across
1 covered metro home to 4.7 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
The basis for “Stagnant pollution mixture”
The October 14 event was elevated across numerous South Coast monitors and accompanied by higher PM10, carbon monoxide, nitrogen dioxide, and sulfur dioxide. The exact-date NWS discussion measured an approximately 11-degree-Celsius marine inversion and the EPA surface packet shows light wind. A basin source-characterization study identifies the recurring PM2.5 mixture as secondary nitrate and sulfate plus organic and elemental carbon. Together these support stagnant anthropogenic mixture at possible confidence without claiming exact component shares or a single emitter.
PossibleThis is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
National Weather Service San Diego Area Forecast Discussion via Iowa Environmental Mesonet · Oct 14, 2002hypothesis
The exact-date NWS discussion measured a roughly 1,500-foot marine layer and an inversion strength near 11 degrees Celsius, strong enough to prevent clearing in some coastal sections. Weak upper-level anticyclonic flow was only beginning to break down, and the event packet reports median surface wind of 2.32 knots. These are strong trapping conditions for an existing regional pollution mixture.
EPA's certified record shows a peak daily PM2.5 value of 82.1 micrograms per cubic meter at San Bernardino. Across the reporting South Coast monitors, median 24-hour FRM PM2.5 was 58.0 and non-FRM PM2.5 was 43.2. PM10 reached a median 77, while carbon monoxide, nitrogen dioxide, and sulfur dioxide also rose above the surrounding-day baseline. The multi-monitor, multi-pollutant pattern is more consistent with basin-wide accumulation of anthropogenic pollution than with an isolated monitor plume.
Inference, not direct attribution
exact_strong_inversion_plus_regional_multipollutant_fingerprint_and_basin_composition_possible.v1: This inference is recorded in the catalog methodology.
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.
exact_strong_inversion_plus_regional_multipollutant_fingerprint_and_basin_composition_possible.v1. This inference is recorded in the catalog methodology.
Inferred
2
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.
Research gap
3
Local response
82.1 µg/m³ near Riverside
EPA monitors recorded the event across 1 metro.
The peak daily concentration is roughly 3.7 cigarette-equivalents at the outdoor daily rate.
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.
Observed context · not attribution
Riverside-San Bernardino-Ontario, CA
Monitor comparison window 2002-10-11 to 2002-10-17 · PM2.5 target: San Bernardino
6 pollutant signals
Fine-particle pulse58 µg/m³
2% above nearby days
Air movement5.5 kt median wind
3 calm hours observed
What observers saw8 mi minimum visibility
0 hours at or below 3 miles
Pollution fingerprint
Metro-wide median of reporting monitors
PM2.558 µg/m³
About the same as surrounding days
Before41.4 µg/m³ Event58 µg/m³ After60.8 µg/m³
PM1031 µg/m³
About the same as surrounding days
Before29 µg/m³ Event31 µg/m³ After32.5 µg/m³
Carbon monoxide0.906 ppm
21% higher than surrounding days
Before0.926 ppm Event0.906 ppm After0.517 ppm
Nitrogen dioxide37.8 ppb
20% higher than surrounding days
Before31.5 ppb Event37.8 ppb After20.9 ppb
Sulfur dioxide1.61 ppb
35% higher than surrounding days
Before1.17 ppb Event1.61 ppb After1.20 ppb
Ozone0.032 ppm
About the same as surrounding days
Before0.026 ppm Event0.032 ppm After0.039 ppm
Atmospheric conditions
PALM SPRINGS RGNL, 77.2 km from the PM2.5 target
Wind5.5 kt median
9 kt maximum · 3 of 24 observed hours calm
Visibility8 mi minimum
0 observed hours at or below 3 miles
Temperature81°F median
73°F to 95°F
Humidity22% median
37% 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.
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.
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.
"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.
3 retained sources
Official record
Strong Southern California marine inversion, October 14, 2002
National Weather Service San Diego Area Forecast Discussion via Iowa Environmental Mesonet
The exact-date NWS discussion measured a roughly 1,500-foot marine layer and an inversion strength near 11 degrees Celsius, strong enough to prevent clearing in some coastal sections. Weak upper-level anticyclonic flow was only beginning to break down, and the event packet reports median surface wind of 2.32 knots. These are strong trapping conditions for an existing regional pollution mixture.
What it supports
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
Limit
The discussion covers extreme southwestern California and the marine layer; it does not directly measure the mixing depth at the San Bernardino monitor or identify emissions.
Official record
San Bernardino and South Coast pollution fingerprint, October 14, 2002
U.S. EPA AirData
EPA's certified record shows a peak daily PM2.5 value of 82.1 micrograms per cubic meter at San Bernardino. Across the reporting South Coast monitors, median 24-hour FRM PM2.5 was 58.0 and non-FRM PM2.5 was 43.2. PM10 reached a median 77, while carbon monoxide, nitrogen dioxide, and sulfur dioxide also rose above the surrounding-day baseline. The multi-monitor, multi-pollutant pattern is more consistent with basin-wide accumulation of anthropogenic pollution than with an isolated monitor plume.
What it supports
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
Limit
The pollutant pattern is descriptive and cannot apportion source sectors or exclude every undocumented smoke contribution.
Scientific research
Characterization of PM2.5 and PM10 in the South Coast Air Basin: spatial variations
Kim et al., Journal of the Air & Waste Management Association
A South Coast AQMD-led basin characterization found that ammonium, nitrate, sulfate, organic carbon, and elemental carbon dominated PM2.5 mass. Nitrate alone contributed 28 to 41 percent and organic carbon 18 to 26 percent across the study, establishing the basin's recurring secondary-plus-combustion particle mixture.
What it supports
Context for the event; this item does not establish the attributed cause by itself.
Limit
The study describes recurring South Coast composition and predates October 2002; it is not an exact-day speciation sample.
What remains uncertain
No exact-date chemical-speciation or receptor-model allocation was recovered.
The result identifies a broad accumulated anthropogenic mixture and does not name a unique emitter.
Status and provenance
PossibleThis 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.