Wildfire smoke High confidence
Daily PM2.5 peaked at 53 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 ≈ 1.8 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 6.9 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
Contemporaneous Colorado reporting and a peer-reviewed Front Range study independently identify Canadian wildfire smoke over Denver and Colorado Springs on July 7, 2015.
High confidence At least two independent causal origins and evidence families agree on this cause.
Atmospheric Chemistry and Physics corroborates
The study identifies July 7, 2015 as one of two wildfire-smoke events measured across the Colorado Front Range.
Colorado Public Radio corroborates
Contemporaneous reporting says Canadian wildfire smoke clouded Denver on July 7 and prompted an extended health warning.
Colorado Public Radio · Jul 8, 2015 corroborates
The report documents smoke drifting south from Canadian wildfires over Denver on July 7 and a Colorado health advisory covering Denver and El Paso County, supporting transported wildfire smoke as the event source.
See every retained source and limitation ↓
Sequence: Denver (Jul 7) → Colorado Springs (Jul 8)
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 study identifies July 7, 2015 as one of two wildfire-smoke events measured across the Colorado Front Range.
View supporting source ↗Air-mass movement
The report documents smoke drifting south from Canadian wildfires over Denver on July 7 and a Colorado health advisory covering Denver and El Paso County, supporting transported wildfire smoke as the event source.
View transport source ↗Local response
EPA monitors recorded the event across 2 metros. The peak daily concentration is roughly 2.4 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 2015-07-04 to 2015-07-11 · PM2.5 target: La Casa
210% above nearby days
9% lower than surrounding days
110% higher than surrounding days
210% higher than surrounding days
110% higher than surrounding days
55% higher than surrounding days
6% higher than surrounding days
40% lower than surrounding days
17% lower than surrounding days
31% higher than surrounding days
About the same as surrounding days
11% lower than surrounding days
9% lower than surrounding days
Colorado Springs, CO
Monitor comparison window 2015-07-04 to 2015-07-11 · PM2.5 target: COLORADO SPRINGS - COLLEGE COLLEGE
315% above nearby days
30% higher than surrounding days
55% higher than surrounding days
315% higher than surrounding days
55% higher than surrounding days
184% higher than surrounding days
11% lower than surrounding days
24% higher than surrounding days
10% lower than surrounding days
30% higher 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.
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 | 53 µg/m³ | 2.4 | Jul 7, 2015 | #15 of its top days |
| Colorado Springs, CO | 27 µg/m³ | 1.2 | Jul 8, 2015 | #19 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.
Atmospheric Chemistry and Physics
The study identifies July 7, 2015 as one of two wildfire-smoke events measured across the Colorado Front Range.
A retained source supports the attributed cause for the stated place and dates.
Colorado Public Radio
Contemporaneous reporting says Canadian wildfire smoke clouded Denver on July 7 and prompted an extended health warning.
A retained source supports the attributed cause for the stated place and dates.
High confidence At least two independent causal origins and evidence families agree on this cause.
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.