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Other Documented

January 2000 San Joaquin Valley limited-dispersion pollution episode

January 7, 2000 to January 10, 2000 · Origin: San Joaquin Valley, California

Daily PM2.5 peaked at 160 µg/m³ near Fresno across 2 covered metros home to 2.1 million 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 ≈ 8.5 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 18 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 “Other”

District evidence identifies a valley-wide January 7–10 episode; the Fresno evidence independently describes the same January episode as accumulated local primary and secondary pollution under limited dispersion. District and measurement-study evidence identify the January 7–10/2–12 San Joaquin Valley winter episode, including the January 9 Fresno maximum and January 7 Bakersfield impacts.

Documented An agency or publisher page assesses this cause, without an agency record naming the event or an EPA qualifier on the data.

San Joaquin Valley Air Pollution Control District · Jan 24, 2005 official

Historical Meteorological Analysis in Support of the 2003 San Joaquin Valley PM10 State Implementation Plan: Final Report

The district's retrospective analysis identifies a valley-wide January 7-10, 2000 PM2.5 episode, including Bakersfield sites, in which primary and secondary pollutants from local emissions accumulated under limited dispersion; it describes strong stability, limited mixing, and nitrate/sulfate formation conditions.

Atmospheric Environment · Jan 1, 2002 corroborates

A wintertime PM2.5 episode at the Fresno, CA, supersite

A measurement study examined the January 2-12 Fresno episode, whose winter maximum occurred January 9, and found evidence consistent with shallow radiation-layer accumulation of urban primary emissions and rapid secondary nitrate formation after daytime coupling to a valley-wide layer.

See every retained source and limitation ↓

Sequence: Bakersfield (Jan 7) → Fresno (Jan 9)

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.

Open the evidence ledger ↓
  1. 1

    Source or mechanism

    Other

    The district's retrospective analysis identifies a valley-wide January 7-10, 2000 PM2.5 episode, including Bakersfield sites, in which primary and secondary pollutants from local emissions accumulated under limited dispersion; it describes strong…

    View supporting source ↗
    Documented
  2. 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. 3

    Local response

    160 µg/m³ near Fresno

    EPA monitors recorded the event across 2 metros. The peak daily concentration is roughly 7.3 cigarette-equivalents at the outdoor daily rate.

    Inspect the pollutant and weather signals ↓
    Documented

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 “Other” explanation; it does not assign the cause by itself.

Observed context · not attribution

Fresno, CA

Monitor comparison window 2000-01-06 to 2000-01-13 · PM2.5 target: 3425 N FIRST ST, FRESNO

4 pollutant signals
Fine-particle pulse 118 µg/m³

54% above nearby days

Air movement 1.43 kt

13% lower than surrounding days

Carbon monoxide 1.55 ppm

8% higher than surrounding days

Pollution fingerprint

Metro-wide median of reporting monitors
PM2.5 118 µg/m³

54% higher than surrounding days

Before67.8 µg/m³ Event118 µg/m³ After35.2 µg/m³
3 monitors · 24 HOUR
Carbon monoxide 1.55 ppm

8% higher than surrounding days

Before1.64 ppm Event1.55 ppm After1.14 ppm
5 monitors · 1 HOUR
Nitrogen dioxide 32.8 ppb

About the same as surrounding days

Before31.3 ppb Event32.8 ppb After26.5 ppb
5 monitors · 1 HOUR
Ozone 0.020 ppm

25% higher than surrounding days

Before0.012 ppm Event0.020 ppm After0.016 ppm
5 monitors · 8-HR RUN AVG BEGIN HOUR

Atmospheric conditions

Nearby EPA weather observations
Humidity 70.4 %

About the same as surrounding days

Pressure 1009 Millibars

About the same as surrounding days

Temperature 44.6 °F

About the same as surrounding days

Wind 1.43 kt

13% 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.

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

Browse the camera map →

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.

Affected metros

MetroPeak PM2.5Cigarettes, whole eventPeak dayAll-time standing
Fresno, CA 160 µg/m³ 13.1 Jan 9, 2000 #4 of its top days
Bakersfield, CA 102.5 µg/m³ 4.7 Jan 7, 2000 #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

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.

Agency and publisher pages 2

  • Historical Meteorological Analysis in Support of the 2003 San Joaquin Valley PM10 State Implementation Plan: Final Report

    San Joaquin Valley Air Pollution Control District · Shawn R. Ferreria and Evan M. Shipp · Jan 24, 2005 official government

    The district's retrospective analysis identifies a valley-wide January 7-10, 2000 PM2.5 episode, including Bakersfield sites, in which primary and secondary pollutants from local emissions accumulated under limited dispersion; it describes strong stability, limited mixing, and nitrate/sulfate formation conditions.

  • A wintertime PM2.5 episode at the Fresno, CA, supersite

    Atmospheric Environment · Jan 1, 2002 corroborates

    A measurement study examined the January 2-12 Fresno episode, whose winter maximum occurred January 9, and found evidence consistent with shallow radiation-layer accumulation of urban primary emissions and rapid secondary nitrate formation after daytime coupling to a valley-wide layer.

What remains uncertain

Status and provenance

Documented An agency or publisher page assesses this cause, without an agency record naming the event or an EPA qualifier on the data.

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.