Wildfire smoke EPA monitor flag
Daily PM2.5 peaked at 239.2 µg/m³ near San Diego across 5 covered metros home to 24 million people. 2 metros recorded their worst day on record; 4 placed a top-ten day.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 11.0 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 266 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
Qualified frozen evidence supports wildfire smoke as the broad root cause and supports grouping the contemporaneous affected events into one time-bounded episode.
EPA monitor flag EPA attached an exceptional-event qualifier to the affected samples. The agency flagged the measurement itself; no separate agency record describes the event.
U.S. EPA Air Quality System and the submitting air monitoring agency · Oct 27, 2003 official
EPA AQS carries an agency-submitted request-exclusion qualifier (E, Forest Fire.) on 4 PM2.5 samples in the candidate CBSA on 2003-10-27, identifying wildfire smoke as affecting the samples. A request-exclusion qualifier is an official submitting-agency causal claim, but this endpoint does not establish EPA concurrence.
U.S. EPA Air Quality System and the submitting air monitoring agency · Oct 26, 2003 official
EPA AQS carries an agency-submitted request-exclusion qualifier (E, Forest Fire.) on 1 PM2.5 sample in the candidate CBSA on 2003-10-26, identifying wildfire smoke as affecting the sample. A request-exclusion qualifier is an official submitting-agency causal claim, but this endpoint does not establish EPA concurrence.
U.S. EPA Air Quality System and the submitting air monitoring agency · Oct 27, 2003 official
EPA AQS carries an agency-submitted request-exclusion qualifier (E, Forest Fire.) on 2 PM2.5 samples in the candidate CBSA on 2003-10-27, identifying wildfire smoke as affecting the samples. A request-exclusion qualifier is an official submitting-agency causal claim, but this endpoint does not establish EPA concurrence.
See every retained source and limitation ↓
Sequence: San Diego (Oct 26) → Los Angeles (Oct 26) → Riverside (Oct 26) → Oxnard (Oct 27) → Las Vegas (Oct 29)
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
EPA AQS carries an agency-submitted request-exclusion qualifier (E, Forest Fire.) on 4 PM2.5 samples in the candidate CBSA on 2003-10-27, identifying wildfire smoke as affecting the samples. A request-exclusion qualifier is an official…
View supporting source ↗Air-mass movement
The NWS assessment documents the late-October Southern California fire outbreak, including the Cedar, Old, Paradise, and Simi fires, and the Santa Ana wind conditions that drove their rapid spread during the event period.
View transport source ↗Local response
EPA monitors recorded the event across 5 metros. The peak daily concentration is roughly 10.9 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 “Wildfire smoke” explanation; it does not assign the cause by itself.
Los Angeles-Long Beach-Anaheim, CA
Monitor comparison window 2003-10-23 to 2003-10-31 · PM2.5 target: Anaheim
75% above nearby days
About the same as surrounding days
13% lower than surrounding days
75% higher than surrounding days
13% lower than surrounding days
24% higher than surrounding days
17% higher than surrounding days
19% higher than surrounding days
About the same as surrounding days
55% lower than surrounding days
About the same as surrounding days
7% higher than surrounding days
About the same as surrounding days
Riverside-San Bernardino-Ontario, CA
Monitor comparison window 2003-10-23 to 2003-10-31 · PM2.5 target: Rubidoux
145% above nearby days
31% lower than surrounding days
33% lower than surrounding days
145% higher than surrounding days
33% lower than surrounding days
22% higher than surrounding days
About the same as surrounding days
33% higher than surrounding days
35% lower than surrounding days
25% lower than surrounding days
About the same as surrounding days
About the same as surrounding days
31% lower than surrounding days
San Diego-Carlsbad, CA
Monitor comparison window 2003-10-23 to 2003-10-31 · PM2.5 target: Chula Vista
330% above nearby days
16% lower than surrounding days
118% higher than surrounding days
330% higher than surrounding days
118% higher than surrounding days
56% higher than surrounding days
64% higher than surrounding days
About the same as surrounding days
31% lower than surrounding days
About the same as surrounding days
About the same as surrounding days
16% lower than surrounding days
Oxnard-Thousand Oaks-Ventura, CA
Monitor comparison window 2003-10-23 to 2003-10-31 · PM2.5 target: Simi Valley-Cochran Street
572% above nearby days
12% higher than surrounding days
113% higher than surrounding days
572% higher than surrounding days
113% higher than surrounding days
50% higher than surrounding days
142% higher than surrounding days
About the same as surrounding days
43% lower than surrounding days
About the same as surrounding days
5% higher than surrounding days
12% higher than surrounding days
Las Vegas-Henderson-Paradise, NV
Monitor comparison window 2003-10-26 to 2003-11-01 · PM2.5 target: Mitchell Street
349% above nearby days
258% higher than surrounding days
349% higher than surrounding days
258% higher than surrounding days
28% higher than surrounding days
16% higher than surrounding days
117% higher than surrounding days
22% 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.
Air-mass reconstruction
NOAA HYSPLIT traces the air arriving at each metro backward for 72 hours. Multiple arrival times and heights show whether the broad path is stable—or sensitive to assumptions about when and where the polluted layer arrived.
Air arriving near Los Angeles-Long Beach-Anaheim
Peak-date arrivals · 2003-10-26
Each line begins 72 hours before arrival and points toward the metro. Color represents arrival height; repeated lines represent 00, 06, 12, and 18 UTC arrival assumptions. A path can show where the air traveled, but it cannot prove which source added the PM2.5.
Air arriving near Oxnard-Thousand Oaks-Ventura
Peak-date arrivals · 2003-10-27
Each line begins 72 hours before arrival and points toward the metro. Color represents arrival height; repeated lines represent 00, 06, 12, and 18 UTC arrival assumptions. A path can show where the air traveled, but it cannot prove which source added the PM2.5.
Air arriving near Riverside-San Bernardino-Ontario
Peak-date arrivals · 2003-10-26
Each line begins 72 hours before arrival and points toward the metro. Color represents arrival height; repeated lines represent 00, 06, 12, and 18 UTC arrival assumptions. A path can show where the air traveled, but it cannot prove which source added the PM2.5.
Air arriving near San Diego-Carlsbad
Peak-date arrivals · 2003-10-27
Each line begins 72 hours before arrival and points toward the metro. Color represents arrival height; repeated lines represent 00, 06, 12, and 18 UTC arrival assumptions. A path can show where the air traveled, but it cannot prove which source added the PM2.5.
Air arriving near Las Vegas-Henderson-Paradise
Peak-date arrivals · 2003-10-29
Each line begins 72 hours before arrival and points toward the metro. Color represents arrival height; repeated lines represent 00, 06, 12, and 18 UTC arrival assumptions. A path can show where the air traveled, but it cannot prove which source added the PM2.5.
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 Diego-Carlsbad, CA | 239.2 µg/m³ | 15.6 | Oct 27, 2003 | Worst day on record |
| Oxnard-Thousand Oaks-Ventura, CA | 116 µg/m³ | 5.3 | Oct 27, 2003 | Worst day on record |
| Los Angeles-Long Beach-Anaheim, CA | 115.5 µg/m³ | 14.5 | Oct 26, 2003 | #3 of its top days |
| Riverside-San Bernardino-Ontario, CA | 104.3 µg/m³ | 12.8 | Oct 26, 2003 | #4 of its top days |
| Las Vegas-Henderson-Paradise, NV | 46.2 µg/m³ | 2.1 | Oct 29, 2003 | #17 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.
AQS PM2.5 qualifier E — Forest Fire.
EPA AQS carries an agency-submitted request-exclusion qualifier (E, Forest Fire.) on 4 PM2.5 samples in the candidate CBSA on 2003-10-27, identifying wildfire smoke as affecting the samples. A request-exclusion qualifier is an official submitting-agency causal claim, but this endpoint does not establish EPA concurrence.
AQS PM2.5 qualifier E — Forest Fire.
EPA AQS carries an agency-submitted request-exclusion qualifier (E, Forest Fire.) on 1 PM2.5 sample in the candidate CBSA on 2003-10-26, identifying wildfire smoke as affecting the sample. A request-exclusion qualifier is an official submitting-agency causal claim, but this endpoint does not establish EPA concurrence.
AQS PM2.5 qualifier E — Forest Fire.
EPA AQS carries an agency-submitted request-exclusion qualifier (E, Forest Fire.) on 2 PM2.5 samples in the candidate CBSA on 2003-10-27, identifying wildfire smoke as affecting the samples. A request-exclusion qualifier is an official submitting-agency causal claim, but this endpoint does not establish EPA concurrence.
Air Quality and the Wildland Fires of Southern California: October 2003
CARB's contemporaneous preliminary review attributes the late-October regional PM2.5 episode to Southern California wildland-fire smoke. Its table reports October 26–28 PM2.5 elevations in the South Coast, San Diego, and Ventura basins, including 239 µg/m³ in San Diego on October 27.
Southern California Wildfires NWS Service Assessment Report 2003
The NWS assessment documents the late-October Southern California fire outbreak, including the Cedar, Old, Paradise, and Simi fires, and the Santa Ana wind conditions that drove their rapid spread during the event period.
EPA monitor flag EPA attached an exceptional-event qualifier to the affected samples. The agency flagged the measurement itself; no separate agency record describes the event.
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.