Peer-reviewed study corroborates
Conditions Leading to Elevated PM2.5 at Near-Road Monitoring Sites
The study identifies Denver's February 10, 2014 57.0 microgram PM2.5 day within a case analysis of meteorological conditions and near-road emissions.
Stagnant pollution mixture Likely
2014-02-10 Denver-Aurora-Lakewood, CO stagnant mixed-pollution episode
Daily PM2.5 peaked at 57 µg/m³ near Denver across 1 covered metro home to 3.1 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 ≈ 2.2 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 6.7 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
The basis for “Stagnant pollution mixture”
A peer-reviewed near-road case study analyzes Denver's exact February 10, 2014 57 microgram PM2.5 day as a meteorology-and-local-emissions episode.
Likely Applicable reporting or a supported inference makes this the best current causal explanation.
Evidence path
From source to city
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.
- 1Documented
Source or mechanism
Stagnant pollution mixture
The study identifies Denver's February 10, 2014 57.0 microgram PM2.5 day within a case analysis of meteorological conditions and near-road emissions.
View supporting source ↗ - 2Research gap
Air-mass movement
The transport path has not been reconstructed
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.
- 3Documented
Local response
57 µg/m³ near Denver
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
What the instruments saw
Before, during, and after the episode: nearby pollutant monitors and surface-weather stations show what changed. This context tests the “Stagnant pollution mixture” explanation; it does not assign the cause by itself.
Colorado Springs, CO
Monitor comparison window 2014-02-07 to 2014-02-13 · PM2.5 target: COLORADO SPRINGS - COLLEGE COLLEGE
84% above nearby days
13 calm hours observed
21 hours at or below 3 miles
Pollution fingerprint
Metro-wide median of reporting monitors PM2.5 26.8 µg/m³
84% higher than surrounding days
Before— Event26.8 µg/m³ After2.30 µg/m³
PM10 34 µg/m³
No adjacent-day comparison
Before— Event34 µg/m³ After—
Carbon monoxide 0.505 ppm
About the same as surrounding days
Before0.513 ppm Event0.505 ppm After0.536 ppm
Sulfur dioxide 3.38 ppb
8% lower than surrounding days
Before3.29 ppb Event3.38 ppb After4.16 ppb
Ozone 0.013 ppm
66% lower than surrounding days
Before0.041 ppm Event0.013 ppm After0.037 ppm
Atmospheric conditions
COLORADO SPRINGS, 12 km from the PM2.5 target9 kt maximum · 13 of 24 observed hours calm
21 observed hours at or below 3 miles
20°F to 30°F
89% maximum
Denver-Aurora-Lakewood, CO
Monitor comparison window 2014-02-07 to 2014-02-13 · PM2.5 target: I-25
469% above nearby days
19% lower than surrounding days
88% higher than surrounding days
Pollution fingerprint
Metro-wide median of reporting monitors PM2.5 45.3 µg/m³
469% higher than surrounding days
Before33.6 µg/m³ Event45.3 µg/m³ After5.70 µg/m³
PM10 63 µg/m³
88% higher than surrounding days
Before37.5 µg/m³ Event63 µg/m³ After20.5 µg/m³
Carbon monoxide 0.568 ppm
12% higher than surrounding days
Before0.506 ppm Event0.568 ppm After0.462 ppm
Nitrogen dioxide 38 ppb
6% higher than surrounding days
Before37.2 ppb Event38 ppb After33.9 ppb
Sulfur dioxide 1.23 ppb
About the same as surrounding days
Before1.67 ppb Event1.23 ppb After1.22 ppb
Ozone 0.025 ppm
31% lower than surrounding days
Before0.036 ppm Event0.025 ppm After0.038 ppm
Atmospheric conditions
Nearby EPA weather observations48% higher than surrounding days
33% lower than surrounding days
19% lower 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.
Measured daily PM2.5 at EPA monitors, as cigarette-equivalents
EPA monitors sit in metro areas, so the colour clusters there. Land between and beyond
them is unmeasured, not clean: this map shows where IAQng has readings, not the extent
of the smoke.
—
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
Camera views near
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.
Affected metros
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| Denver-Aurora-Lakewood, CO | 57 µg/m³ | 2.6 | Feb 10, 2014 | #10 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
What supports this account
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.
Conditions Leading to Elevated PM2.5 at Near-Road Monitoring Sites
Peer-reviewed study
The study identifies Denver's February 10, 2014 57.0 microgram PM2.5 day within a case analysis of meteorological conditions and near-road emissions.
What it supports
A retained source supports the attributed cause for the stated place and dates.
Limit
The accessible result directly supports Denver but not Colorado Springs.
What remains uncertain
- The classification is bounded to the retained evidence and does not apportion every source contributing to the daily PM2.5 value.
Status and provenance
Likely Applicable reporting or a supported inference makes this the best current causal explanation.
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.