Wildfire smoke EPA monitor flag
Daily PM2.5 peaked at 95.9 µg/m³ near Seattle across 1 covered metro home to 4.1 million people.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 4.0 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 16 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.
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 · Aug 14, 2018 official
EPA AQS carries an agency-submitted informational qualifier (IT, Wildfire-U. S.) on 215 PM2.5 samples in the candidate CBSA on 2018-08-14, 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.
Spokane Regional Clean Air Agency · Aug 1, 2018 official
The agency reports widespread heavy smoke across Washington in August 2018 from wildfires in British Columbia, Washington, Oregon, Idaho, Montana, and California.
NOAA/NCEI Storm Events Database · Aug 3, 2018 corroborates
An air quality sensor at Winthrop recorded Unhealthy air quality from August 3rd through August 27th with occasional spikes into the Very Unhealthy category.
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 215 PM2.5 samples in the candidate CBSA on 2018-08-14, identifying wildfire smoke as affecting the samples. An informational qualifier is an official…
View supporting source ↗Air-mass movement
NOAA HYSPLIT modeled 12 backward paths across multiple arrival times and heights. They show where the air traveled, not which source polluted it.
Explore the modeled paths ↓Local response
The state described widespread 2018 wildfire-smoke impacts as the season intensified, corroborating the regional smoke episode.
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.
Seattle-Tacoma-Bellevue, WA
Monitor comparison window 2018-08-11 to 2018-08-17 · PM2.5 target: DARRINGTON - FIR ST (Darrington High School)
207% above nearby days
5% lower than surrounding days
70% higher than surrounding days
207% higher than surrounding days
70% higher than surrounding days
77% higher than surrounding days
46% higher than surrounding days
105% higher than surrounding days
6% lower than surrounding days
About the same as surrounding days
7% higher than surrounding days
5% 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 Seattle-Tacoma-Bellevue
Peak-date arrivals · 2018-08-14
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 | 95.9 µg/m³ | 4.4 | Aug 14, 2018 | #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 215 PM2.5 samples in the candidate CBSA on 2018-08-14, 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.
NWS Dense Smoke record, EAST SLOPES NORTHERN CASCADES, WASHINGTON (2018-08-03)
An air quality sensor at Winthrop recorded Unhealthy air quality from August 3rd through August 27th with occasional spikes into the Very Unhealthy category.
NWS Dense Smoke record, OKANOGAN HIGHLANDS, WASHINGTON (2018-08-03)
An air quality sensor in Inchelium recorded periods of Unhealthy air quality due to smoke from area wildfires through much of August.
NWS Dense Smoke record, OKANOGAN HIGHLANDS, WASHINGTON (2018-08-03)
An air quality sensor in Nespelem recorded periods of Unhealthy air quality due to smoke from area wildfires through much of August.
NWS Dense Smoke record, OKANOGAN HIGHLANDS, WASHINGTON (2018-08-03)
An air quality sensor in Republic recorded almost continuous Unhealthy air quality due to smoke from area wildfires through much of August.
NWS Dense Smoke record, OKANOGAN VALLEY, WASHINGTON (2018-08-03)
The air quality sensor at Omak recorded Unhealthy air quality through most of the month of August.
NWS Dense Smoke record, NORTHEAST MOUNTAINS, WASHINGTON (2018-08-03)
An air quality sensor in Colville recorded occasional periods of Unhealthy air quality with a few spikes into the Very Unhealthy range due to smoke from area wildfires through much of August.
NWS Dense Smoke record, EAST SLOPES NORTHERN CASCADES, WASHINGTON (2018-08-03)
An air quality sensor at Twisp recorded Unhealthy air quality from August 3rd through August 27th with occasional spikes into the Hazardous category.
Air Quality Report: August 2018
The agency reports widespread heavy smoke across Washington in August 2018 from wildfires in British Columbia, Washington, Oregon, Idaho, Montana, and California.
Wildfire smoke triggers report to EPA
The state described widespread 2018 wildfire-smoke impacts as the season intensified, corroborating the regional smoke 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.
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.