Wildfire smoke Agency determination
Daily PM2.5 peaked at 70.3 µg/m³ near Seattle across 2 covered metros home to 6.7 million people.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 3.8 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 26 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 for this time-bounded episode.
Agency determination A government body issued a record naming this cause for this event: an NWS air-quality alert, a NOAA Storm Events record, or a state or local official archive.
U.S. EPA Air Quality System and the submitting air monitoring agency · Sep 5, 2017 official
EPA AQS carries an agency-submitted informational qualifier (IT, Wildfire-U. S.) on 21 PM2.5 samples in the candidate CBSA on 2017-09-05, identifying wildfire smoke as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
U.S. EPA Air Quality System and the submitting air monitoring agency · Sep 5, 2017 official
EPA AQS carries an agency-submitted informational qualifier (IT, Wildfire-U. S.) on 168 PM2.5 samples in the candidate CBSA on 2017-09-05, identifying wildfire smoke as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
U.S. EPA Air Quality System and the submitting air monitoring agency · Sep 6, 2017 official
EPA AQS carries an agency-submitted informational qualifier (IT, Wildfire-U. S.) on 24 PM2.5 samples in the candidate CBSA on 2017-09-06, identifying wildfire smoke as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
See every retained source and limitation ↓
Sequence: Portland (Sep 5) → Seattle (Sep 6)
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 informational qualifier (IT, Wildfire-U. S.) on 21 PM2.5 samples in the candidate CBSA on 2017-09-05, identifying wildfire smoke as affecting the samples. An informational qualifier is an official…
View supporting source ↗Air-mass movement
Contemporaneous reporting described smoke and ash from central Washington wildfires over Seattle and a satellite image showing smoke across Washington, Oregon, and Idaho.
View transport source ↗Local response
EPA monitors recorded the event across 2 metros. The peak daily concentration is roughly 3.2 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.
Portland-Vancouver-Hillsboro, OR-WA
Monitor comparison window 2017-09-02 to 2017-09-09 · PM2.5 target: Gresham - Gresham Learning Center (GLC)
432% above nearby days
16% lower than surrounding days
87% higher than surrounding days
432% higher than surrounding days
87% higher than surrounding days
22% higher than surrounding days
18% lower than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
16% lower than surrounding days
Seattle-Tacoma-Bellevue, WA
Monitor comparison window 2017-09-02 to 2017-09-09 · PM2.5 target: NORTH BEND - NORTH BEND WAY
198% above nearby days
13% lower than surrounding days
50% higher than surrounding days
198% higher than surrounding days
50% higher than surrounding days
45% higher than surrounding days
111% higher than surrounding days
25% lower than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
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.
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 Portland-Vancouver-Hillsboro
Peak-date arrivals · 2017-09-05
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 Seattle-Tacoma-Bellevue
Peak-date arrivals · 2017-09-06
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 |
|---|---|---|---|---|
| Seattle-Tacoma-Bellevue, WA | 70.3 µg/m³ | 3.2 | Sep 6, 2017 | #19 of its top days |
| Portland-Vancouver-Hillsboro, OR-WA | 70 µg/m³ | 6.1 | Sep 5, 2017 | #13 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 IT — Wildfire-U. S.
EPA AQS carries an agency-submitted informational qualifier (IT, Wildfire-U. S.) on 21 PM2.5 samples in the candidate CBSA on 2017-09-05, identifying wildfire smoke as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
AQS PM2.5 qualifier IT — Wildfire-U. S.
EPA AQS carries an agency-submitted informational qualifier (IT, Wildfire-U. S.) on 168 PM2.5 samples in the candidate CBSA on 2017-09-05, identifying wildfire smoke as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
AQS PM2.5 qualifier IT — Wildfire-U. S.
EPA AQS carries an agency-submitted informational qualifier (IT, Wildfire-U. S.) on 24 PM2.5 samples in the candidate CBSA on 2017-09-06, identifying wildfire smoke as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
AQS PM2.5 qualifier IT — Wildfire-U. S.
EPA AQS carries an agency-submitted informational qualifier (IT, Wildfire-U. S.) on 144 PM2.5 samples in the candidate CBSA on 2017-09-06, identifying wildfire smoke as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
An archived NWS Air Quality Alert for Seattle-Tacoma-Bellevue, WA, issued 2017-09-06T16:56Z, explicitly identifies wildfire smoke. IEM is the archive, not the official system of record.
NWS Dense Smoke record, SPOKANE AREA, WASHINGTON (2017-09-04)
The Spokane Regional Clean Air Agency reported Very Unhealthy air quality at their monitoring station in Spokane.
NWS Dense Smoke record, OKANOGAN VALLEY, WASHINGTON (2017-09-04)
The Washington State Department of Ecology reported Very Unhealthy air quality readings at their monitoring station at Omak.
NWS Dense Smoke record, NORTHEAST MOUNTAINS, WASHINGTON (2017-09-04)
The Washington State Department of Ecology reported Hazardous air quality readings at their monitoring station in Newport.
NWS Dense Smoke record, WENATCHEE AREA, WASHINGTON (2017-09-04)
The Washington State Department of Ecology reported Very Unhealthy air quality readings at their monitoring station in Wenatchee.
NWS Dense Smoke record, WASHINGTON PALOUSE, WASHINGTON (2017-09-04)
The Washington State Department of Ecology reported Hazardous air quality readings at their monitoring station in Pullman and Rosalia.
Portland Fire & Rescue Joins Mutual Aid Task Force
Portland Fire & Rescue reported deployment to the Eagle Creek wildfire on September 5 and directed residents to wildfire-smoke health guidance, corroborating that the Portland portion of the event coincided with the active regional wildfire-smoke episode.
Central WA wildfires shroud Seattle in ash, smoke
Contemporaneous reporting described smoke and ash from central Washington wildfires over Seattle and a satellite image showing smoke across Washington, Oregon, and Idaho.
Agency determination A government body issued a record naming this cause for this event: an NWS air-quality alert, a NOAA Storm Events record, or a state or local official archive.
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.