Wildfire smoke Agency determination
Named source Cameron Peak Fire 208,913 acres , CO · IRWIN 2020-COARF-000636
Daily PM2.5 peaked at 51.6 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 ≈ 3.5 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 13 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.
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.
National Weather Service via Iowa Environmental Mesonet archive · Aug 22, 2020 official
An archived NWS Air Quality Alert for Denver-Aurora-Lakewood, CO, issued 2020-08-22T15:10Z, explicitly identifies wildfire smoke. IEM is the archive, not the official system of record.
Denver7 · Aug 22, 2020 corroborates
Contemporaneous coverage relayed a National Weather Service forecast that Cameron Peak Fire smoke would drift south toward Denver, with unhealthy visibility conditions.
See every retained source and limitation ↓
Sequence: Denver (Aug 22) → Colorado Springs (Aug 22)
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
An archived NWS Air Quality Alert for Denver-Aurora-Lakewood, CO, issued 2020-08-22T15:10Z, explicitly identifies wildfire smoke. IEM is the archive, not the official system of record.
View supporting source ↗Air-mass movement
Contemporaneous coverage relayed a National Weather Service forecast that Cameron Peak Fire smoke would drift south toward Denver, with unhealthy visibility conditions.
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.
Colorado Springs, CO
Monitor comparison window 2020-08-19 to 2020-08-26 · PM2.5 target: COLORADO SPRINGS - COLLEGE COLLEGE
51% above nearby days
24% lower than surrounding days
13% higher than surrounding days
51% higher than surrounding days
13% higher than surrounding days
About the same as surrounding days
6% higher than surrounding days
21% lower than surrounding days
About the same as surrounding days
24% lower than surrounding days
Denver-Aurora-Lakewood, CO
Monitor comparison window 2020-08-19 to 2020-08-26 · PM2.5 target: La Casa
57% above nearby days
About the same as surrounding days
6% higher than surrounding days
57% higher than surrounding days
6% higher than surrounding days
11% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
8% higher than surrounding days
19% lower than surrounding days
About the same as surrounding days
About the same as 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.
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 | 51.6 µg/m³ | 4.6 | Aug 22, 2020 | #16 of its top days |
| Colorado Springs, CO | 28.7 µg/m³ | 2.6 | Aug 22, 2020 | #14 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.
An archived NWS Air Quality Alert for Denver-Aurora-Lakewood, CO, issued 2020-08-22T15:10Z, explicitly identifies wildfire smoke. IEM is the archive, not the official system of record.
Cameron Peak fire 18,287 acres, 0% contained in Larimer County
Contemporaneous coverage relayed a National Weather Service forecast that Cameron Peak Fire smoke would drift south toward Denver, with unhealthy visibility conditions.
NASA documented the widespread early-September western wildfire-smoke episode and specifically noted Colorado fire activity and unhealthy-air warnings; it does not directly attribute the August 22 metro measurements.
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.