Stagnant pollution mixture Possible
Daily PM2.5 peaked at 44.3 µg/m³ near Winston across 1 covered metro home to 705,187 people.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 1.5 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 1.1 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
Exact-date NWS and nearby surface observations document stagnant air, light winds, and haze during a five-monitor PM2.5 episode with elevated combustion tracers. The evidence supports a possible trapped anthropogenic mixture but not a specific source allocation.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
NOAA/NWS surface observations via Iowa Environmental Mesonet · Jan 12, 2005 hypothesis
The Winston-Salem airport, about 2.5 km from the Hattie Avenue PM2.5 monitor, reported haze during six local hours. The daily median wind was about 4.5 knots, with one calm hour and four hours at or below 3 knots; visibility was 3 miles or less for eight hours.
National Weather Service Raleigh via Iowa Environmental Mesonet · Jan 12, 2005 hypothesis
Early on January 12, NWS Raleigh described light to mostly calm winds and stagnant air across central North Carolina, with radiational cooling and thickening fog expected toward daybreak. It expected winds to strengthen later as the pressure gradient tightened.
U.S. EPA AirData hypothesis
IAQng's reproducible EPA-row aggregation found a metro-wide particle episode on January 12: the five-monitor PM2.5 median was 44.3 µg/m³ versus 16.5 before and 8.6 after, while PM10 was 31.5 µg/m³. CO and NO2 were also above their surrounding-window medians, consistent with accumulated combustion pollution rather than an isolated PM2.5-only reading.
Inference, not direct attribution
documented_stagnation_overlap_possible.v1: This inference is recorded in the catalog methodology.
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
documented_stagnation_overlap_possible.v1. This inference is recorded in the catalog methodology.
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
EPA monitors recorded the event across 1 metro. The peak daily concentration is roughly 2.0 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 “Stagnant pollution mixture” explanation; it does not assign the cause by itself.
Winston-Salem, NC
Monitor comparison window 2005-01-09 to 2005-01-15 · PM2.5 target: Hattie Avenue
334% above nearby days
About the same as surrounding days
97% higher than surrounding days
334% higher than surrounding days
97% higher than surrounding days
64% higher than surrounding days
103% higher than surrounding days
About the same as surrounding days
27% higher than surrounding days
15% 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.
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 |
|---|---|---|---|---|
| Winston-Salem, NC | 44.3 µg/m³ | 2.0 | Jan 12, 2005 | #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.
NOAA/NWS surface observations via Iowa Environmental Mesonet
The Winston-Salem airport, about 2.5 km from the Hattie Avenue PM2.5 monitor, reported haze during six local hours. The daily median wind was about 4.5 knots, with one calm hour and four hours at or below 3 knots; visibility was 3 miles or less for eight hours.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
Haze and reduced visibility corroborate the local accumulation setting but do not identify the particle sources.
National Weather Service Raleigh via Iowa Environmental Mesonet
Early on January 12, NWS Raleigh described light to mostly calm winds and stagnant air across central North Carolina, with radiational cooling and thickening fog expected toward daybreak. It expected winds to strengthen later as the pressure gradient tightened.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The discussion documents a trapping setting early in the day, not a specific emissions source or an all-day stagnant period.
U.S. EPA AirData
IAQng's reproducible EPA-row aggregation found a metro-wide particle episode on January 12: the five-monitor PM2.5 median was 44.3 µg/m³ versus 16.5 before and 8.6 after, while PM10 was 31.5 µg/m³. CO and NO2 were also above their surrounding-window medians, consistent with accumulated combustion pollution rather than an isolated PM2.5-only reading.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The measurements identify a mixed accumulation episode but do not apportion it among traffic, industry, residential combustion, or other sources.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
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.