Wildfire smoke Agency determination provisional
Daily PM2.5 peaked at 57.7 µg/m³ near Boise City across 1 covered metro home to 845,877 people.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 4.5 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 3.8 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 supplied evidence supports wildfire smoke for the July 20–21 Boise City event. No other supplied event was merged without evidence of the same coherent occurrence.
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.
Idaho Department of Environmental Quality · Jul 20, 2026 official
Idaho DEQ's July 20 advisory explicitly attributed degraded air quality in the Boise area to wildfire smoke. IEM is the archive, not the official system of record.
National Weather Service / Idaho Department of Environmental Quality · Jul 20, 2026 official
The Idaho DEQ advisory for Ada County, including Boise, attributed degraded air quality to wildfire smoke and forecast unhealthy AQI.
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
Idaho DEQ's July 20 advisory explicitly attributed degraded air quality in the Boise area to wildfire smoke. IEM is the archive, not the official system of record.
View supporting source ↗Air-mass movement
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.
Local response
EPA monitors recorded the event across 1 metro. The peak daily concentration is roughly 2.6 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.
Boise City, ID
Monitor comparison window 2026-07-17 to 2026-07-24
The PM2.5 event remains in the catalog, but the surrounding monitoring record cannot supply a defensible instrument fingerprint for this place and date.
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 |
|---|---|---|---|---|
| Boise City, ID | 57.7 µg/m³ | 5.1 | Jul 20, 2026 | #21 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.
Idaho air-quality advisory due to wildfire smoke
Idaho DEQ's July 20 advisory explicitly attributed degraded air quality in the Boise area to wildfire smoke. IEM is the archive, not the official system of record.
Air Quality Alert for Boise, Idaho
The Idaho DEQ advisory for Ada County, including Boise, attributed degraded air quality to wildfire smoke and forecast unhealthy AQI.
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. Recent days are preliminary AirNow readings and re-rank once EPA certifies them. 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.