Wildfire smoke Corroborated
Named source Cameron Peak Fire 208,913 acres , CO · IRWIN 2020-COARF-000636
Daily PM2.5 peaked at 49.7 µg/m³ near Denver across 2 covered metros home to 3.8 million people.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 1.7 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 6.5 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
Supplied qualified evidence supports wildfire-smoke as the root cause. The grouping includes only events linked by explicit shared episode evidence; otherwise this remains a single-event episode.
Corroborated Independent reporting agrees on the cause, with no agency determination, monitor flag, or published assessment behind it.
KRDO · Sep 6, 2020 corroborates
Contemporaneous reporting states that Cameron Peak Fire smoke affected Front Range air quality; it reports a state particulate action day and degraded Denver conditions.
CBS Colorado · Sep 7, 2020 corroborates
Coverage reports the Cameron Peak Fire smoke plume being carried into the Denver metro area from September 6-7.
See every retained source and limitation ↓
Sequence: Denver (Sep 6) → Colorado Springs (Sep 7)
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
Contemporaneous reporting states that Cameron Peak Fire smoke affected Front Range air quality; it reports a state particulate action day and degraded Denver conditions.
View supporting source ↗Air-mass movement
Coverage reports the Cameron Peak Fire smoke plume being carried into the Denver metro area from September 6-7.
View transport source ↗Local response
EPA monitors recorded the event across 2 metros. The peak daily concentration is roughly 2.3 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.
Denver-Aurora-Lakewood, CO
Monitor comparison window 2020-09-03 to 2020-09-10 · PM2.5 target: La Casa
232% above nearby days
37% higher than surrounding days
75% higher than surrounding days
232% higher than surrounding days
75% higher than surrounding days
24% higher than surrounding days
7% lower than surrounding days
42% higher than surrounding days
6% higher than surrounding days
21% lower than surrounding days
About the same as surrounding days
7% higher than surrounding days
37% higher than surrounding days
Colorado Springs, CO
Monitor comparison window 2020-09-03 to 2020-09-10 · PM2.5 target: COLORADO SPRINGS - COLLEGE COLLEGE
242% above nearby days
About the same as surrounding days
No adjacent-day comparison
242% higher than surrounding days
No adjacent-day comparison
18% higher than surrounding days
16% lower than surrounding days
21% higher than surrounding days
29% lower than surrounding days
10% higher 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 · 2020-09-07
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 · 2020-09-06
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 |
|---|---|---|---|---|
| Denver-Aurora-Lakewood, CO | 49.7 µg/m³ | 2.3 | Sep 6, 2020 | #17 of its top days |
| Colorado Springs, CO | 27.7 µg/m³ | 1.3 | Sep 7, 2020 | #17 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.
Smoky Sunday: Cameron Peak Fire affects air quality across the Front Range
Contemporaneous reporting states that Cameron Peak Fire smoke affected Front Range air quality; it reports a state particulate action day and degraded Denver conditions.
Cameron Peak Fire Creates Huge Smoke Plume, Unhealthy Air Conditions
Coverage reports the Cameron Peak Fire smoke plume being carried into the Denver metro area from September 6-7.
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.