Wildfire smoke Corroborated
Daily PM2.5 peaked at 55.4 µg/m³ near Denver across 2 covered metros home to 3.8 million 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 ≈ 2.4 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 9.2 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.
Corroborated Independent reporting agrees on the cause, with no agency determination, monitor flag, or published assessment behind it.
Denver7 · Aug 1, 2018 corroborates
The report cites a Colorado health advisory and states that smoke from U.S. wildfires blanketed eastern Colorado, with unhealthy fine-particle forecasts in the Denver metro. It corroborates wildfire-smoke influence in the episode window but does not quantify smoke-attributable PM2.5.
greeleytribune.com · Aug 20, 2018 corroborates
koaa.com · Aug 22, 2018 corroborates
See every retained source and limitation ↓
Sequence: Denver (Aug 20) → Colorado Springs (Aug 20)
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
The report cites a Colorado health advisory and states that smoke from U.S. wildfires blanketed eastern Colorado, with unhealthy fine-particle forecasts in the Denver metro. It corroborates wildfire-smoke influence in the episode window but does not…
View supporting source ↗Air-mass movement
NOAA HYSPLIT modeled 24 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
EPA monitors recorded the event across 2 metros. The peak daily concentration is roughly 2.5 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.
Colorado Springs, CO
Monitor comparison window 2018-08-17 to 2018-08-25 · PM2.5 target: COLORADO SPRINGS - COLLEGE COLLEGE
113% above nearby days
About the same as surrounding days
11% higher than surrounding days
113% higher than surrounding days
11% higher than surrounding days
36% higher than surrounding days
7% lower than surrounding days
8% higher than surrounding days
6% lower than surrounding days
About the same as surrounding days
Denver-Aurora-Lakewood, CO
Monitor comparison window 2018-08-17 to 2018-08-25 · PM2.5 target: Globeville
84% above nearby days
About the same as surrounding days
About the same as surrounding days
84% higher than surrounding days
About the same as surrounding days
12% higher than surrounding days
32% higher than surrounding days
15% lower than surrounding days
17% lower than surrounding days
18% higher than surrounding days
About the same as surrounding days
7% lower than surrounding days
About the same as 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 Colorado Springs
Peak-date arrivals · 2018-08-21
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 Denver-Aurora-Lakewood
Peak-date arrivals · 2018-08-20
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 |
|---|---|---|---|---|
| Denver-Aurora-Lakewood, CO | 55.4 µg/m³ | 2.5 | Aug 20, 2018 | #12 of its top days |
| Colorado Springs, CO | 35.6 µg/m³ | 4.2 | Aug 21, 2018 | #5 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.
Air quality advisory for wildfire smoke in effect for eastern Colorado
The report cites a Colorado health advisory and states that smoke from U.S. wildfires blanketed eastern Colorado, with unhealthy fine-particle forecasts in the Denver metro. It corroborates wildfire-smoke influence in the episode window but does not quantify smoke-attributable PM2.5.
Corroborated Independent reporting agrees on the cause, with no agency determination, monitor flag, or published assessment behind it.
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.