Wildfire smoke EPA monitor flag
Named source Thomas Fire 281,893 acres , CA · IRWIN 2017-CAVNC-103156
Daily PM2.5 peaked at 100.7 µg/m³ near Oxnard across 1 covered metro home to 835,427 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 ≈ 7.2 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 6.0 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 cause and supports grouping 2 records into the same time-bounded occurrence.
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 · Dec 13, 2017 official
EPA AQS carries an agency-submitted request-exclusion qualifier (RT, Wildfire-U. S.) on 48 PM2.5 samples in the candidate CBSA on 2017-12-13, 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 · Dec 16, 2017 official
EPA AQS carries an agency-submitted request-exclusion qualifier (RT, Wildfire-U. S.) on 48 PM2.5 samples in the candidate CBSA on 2017-12-16, 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 · Dec 15, 2017 official
EPA AQS carries an agency-submitted request-exclusion qualifier (RT, Wildfire-U. S.) on 48 PM2.5 samples in the candidate CBSA on 2017-12-15, 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.
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 (RT, Wildfire-U. S.) on 48 PM2.5 samples in the candidate CBSA on 2017-12-13, identifying wildfire smoke as affecting the samples. A request-exclusion qualifier is an official…
View supporting source ↗Air-mass movement
NOAA satellite-smoke analysis identified the observed southern California smoke as almost certainly from the Thomas Fire in Ventura County.
View transport source ↗Local response
The City of Ventura states that the December 2017 Thomas Fire moved through Ventura County and records smoke and ash impacts.
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.
Oxnard-Thousand Oaks-Ventura, CA
Monitor comparison window 2017-12-12 to 2017-12-19 · PM2.5 target: Ojai - East Ojai Ave
164% above nearby days
19% lower than surrounding days
43% higher than surrounding days
164% higher than surrounding days
43% higher than surrounding days
26% higher than surrounding days
About the same as surrounding days
58% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
19% 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.
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 |
|---|---|---|---|---|
| Oxnard-Thousand Oaks-Ventura, CA | 100.7 µg/m³ | 8.6 | Dec 16, 2017 | #2 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 RT — Wildfire-U. S.
EPA AQS carries an agency-submitted request-exclusion qualifier (RT, Wildfire-U. S.) on 48 PM2.5 samples in the candidate CBSA on 2017-12-13, 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 RT — Wildfire-U. S.
EPA AQS carries an agency-submitted request-exclusion qualifier (RT, Wildfire-U. S.) on 48 PM2.5 samples in the candidate CBSA on 2017-12-16, 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 RT — Wildfire-U. S.
EPA AQS carries an agency-submitted request-exclusion qualifier (RT, Wildfire-U. S.) on 48 PM2.5 samples in the candidate CBSA on 2017-12-15, 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.
CAL FIRE identifies the Thomas Fire as an active December 2017 wildfire in Ventura and Santa Barbara counties, placing the Oxnard-area event within the fire's smoke-impacted period.
Smoke Advisory for the Thomas Fire
The air district issued a December 16 smoke advisory citing shifting winds and ongoing smoke from the Thomas Fire burning in Ventura and Santa Barbara counties.
The City of Ventura states that the December 2017 Thomas Fire moved through Ventura County and records smoke and ash impacts.
Smoke Text Product - Satellite Services Division
NOAA satellite-smoke analysis identified the observed southern California smoke as almost certainly from the Thomas Fire in Ventura County.
Cited authorities: CAL FIRE
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.