Winter inversion Corroborated
Daily PM2.5 peaked at 58.6 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 ≈ 2.0 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 7.8 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
State-agency meteorological attribution reported by Colorado Public Radio identifies a strong inversion that trapped local emissions in the Denver metro area; a National Park Service evaluation independently documents elevated PM2.5 during the same early-March period.
Corroborated Independent reporting agrees on the cause, with no agency determination, monitor flag, or published assessment behind it.
Colorado Public Radio · Mar 6, 2019 corroborates
Colorado Public Radio reported a Colorado Air Pollution Control Division meteorologist’s assessment that a strong inversion trapped local emissions near the surface, producing high fine-particle levels in the Denver metro area.
U.S. National Park Service corroborates
A National Park Service evaluation using the state-operated Denver I-25 reference monitor documents elevated PM2.5 for approximately three days in the first week of March 2019, including a 77 µg/m³ reference-monitor concentration on March 7.
See every retained source and limitation ↓
Sequence: Denver (Mar 6) → Colorado Springs (Mar 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
Colorado Public Radio reported a Colorado Air Pollution Control Division meteorologist’s assessment that a strong inversion trapped local emissions near the surface, producing high fine-particle levels in the Denver metro area.
View supporting source ↗Air-mass movement
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.
Local response
A National Park Service evaluation using the state-operated Denver I-25 reference monitor documents elevated PM2.5 for approximately three days in the first week of March 2019, including a 77 µg/m³ reference-monitor concentration on March 7.
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 “Winter inversion” explanation; it does not assign the cause by itself.
Denver-Aurora-Lakewood, CO
Monitor comparison window 2019-03-03 to 2019-03-10 · PM2.5 target: La Casa
105% above nearby days
9% lower than surrounding days
58% higher than surrounding days
105% higher than surrounding days
58% higher than surrounding days
15% higher than surrounding days
27% higher than surrounding days
70% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
9% lower than surrounding days
Colorado Springs, CO
Monitor comparison window 2019-03-03 to 2019-03-10 · PM2.5 target: COLORADO SPRINGS - COLLEGE COLLEGE
135% above nearby days
34% lower than surrounding days
26% higher than surrounding days
135% higher than surrounding days
26% higher than surrounding days
17% higher than surrounding days
15% lower than surrounding days
About the same as surrounding days
7% higher than surrounding days
34% 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.
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 | 58.6 µg/m³ | 2.7 | Mar 6, 2019 | #8 of its top days |
| Colorado Springs, CO | 28.4 µg/m³ | 1.3 | Mar 7, 2019 | #15 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.
A Low-cost Air Quality Sensor for Measuring Particulate Matter
A National Park Service evaluation using the state-operated Denver I-25 reference monitor documents elevated PM2.5 for approximately three days in the first week of March 2019, including a 77 µg/m³ reference-monitor concentration on March 7.
Blame The Cold For Denver’s Smog This Week
Colorado Public Radio reported a Colorado Air Pollution Control Division meteorologist’s assessment that a strong inversion trapped local emissions near the surface, producing high fine-particle levels in the Denver metro area.
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.