NASA Earth Observatory · Aug 4, 2006 official
Haze over the Eastern United States
NASA says air quality dropped when an early-August 2006 heat wave trapped pollution over many East Coast cities.
Stagnant pollution mixture Possible
2006-07-31 to 2006-08-01 Durham-Chapel Hill, NC, Greensboro-High Point, NC, and 1 other metros stagnant mixed-pollution episode
Daily PM2.5 peaked at 41.1 µg/m³ near Raleigh across 3 covered metros home to 3.0 million people.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 1.4 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 4.1 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
The basis for “Stagnant pollution mixture”
Manual research connected 3 source events to one stagnant mixed-pollution episode using the deterministic grouping rule.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
See every retained source and limitation ↓
Sequence: Greensboro (Jul 31) → Raleigh (Aug 1) → Durham (Aug 1)
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
NASA says air quality dropped when an early-August 2006 heat wave trapped pollution over many East Coast cities.
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
41.1 µg/m³ near Raleigh
EPA monitors recorded the event across 3 metros. The peak daily concentration is roughly 1.9 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.
Raleigh, NC
Monitor comparison window 2006-07-29 to 2006-08-04 · PM2.5 target: Millbrook School
32% above nearby days
42% higher than surrounding days
Pollution fingerprint
Metro-wide median of reporting monitors PM2.5 41.1 µg/m³
32% higher than surrounding days
Before20.3 µg/m³ Event41.1 µg/m³ After31.2 µg/m³
Carbon monoxide 0.765 ppm
42% higher than surrounding days
Before0.370 ppm Event0.765 ppm After0.630 ppm
Sulfur dioxide 1.91 ppb
About the same as surrounding days
Before2.52 ppb Event1.91 ppb After1.87 ppb
Ozone 0.040 ppm
About the same as surrounding days
Before0.033 ppm Event0.040 ppm After0.049 ppm
Atmospheric conditions
Nearby EPA weather observationsAbout the same as surrounding days
About the same as surrounding days
Greensboro-High Point, NC
Monitor comparison window 2006-07-28 to 2006-08-03 · PM2.5 target: Mendenhall School
45% above nearby days
Pollution fingerprint
Metro-wide median of reporting monitors PM2.5 39.4 µg/m³
45% higher than surrounding days
Before19.1 µg/m³ Event39.4 µg/m³ After31.8 µg/m³
Ozone 0.032 ppm
7% lower than surrounding days
Before0.028 ppm Event0.032 ppm After0.042 ppm
Atmospheric conditions
Nearby EPA weather observationsAbout the same as surrounding days
About the same as surrounding days
Durham-Chapel Hill, NC
Monitor comparison window 2006-07-29 to 2006-08-04
51% above nearby days
39% higher than surrounding days
Pollution fingerprint
Metro-wide median of reporting monitors PM2.5 36.5 µg/m³
51% higher than surrounding days
Before21.7 µg/m³ Event36.5 µg/m³ After24.2 µg/m³
Carbon monoxide 0.591 ppm
39% higher than surrounding days
Before0.352 ppm Event0.591 ppm After0.426 ppm
Ozone 0.036 ppm
About the same as surrounding days
Before0.026 ppm Event0.036 ppm After0.046 ppm
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.
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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 |
|---|---|---|---|---|
| Raleigh, NC | 41.1 µg/m³ | 1.9 | Aug 1, 2006 | #15 of its top days |
| Greensboro-High Point, NC | 39.4 µg/m³ | 1.8 | Jul 31, 2006 | #24 of its top days |
| Durham-Chapel Hill, NC | 36.5 µg/m³ | 1.7 | Aug 1, 2006 | #24 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.
Haze over the Eastern United States
NASA Earth Observatory
NASA says air quality dropped when an early-August 2006 heat wave trapped pollution over many East Coast cities.
What it supports
An official source supports the attributed cause for the stated place and dates.
Limit
The NASA collection describes the regional episode and mechanism but does not apportion the individual metro-day measurement.
Haze over the Eastern United States
NASA Earth Observatory
NASA says air quality dropped when an early-August 2006 heat wave trapped pollution over many East Coast cities.
What it supports
An official source supports the attributed cause for the stated place and dates.
Limit
The NASA collection describes the regional episode and mechanism but does not apportion the individual metro-day measurement.
Haze over the Eastern United States
NASA Earth Observatory
NASA says air quality dropped when an early-August 2006 heat wave trapped pollution over many East Coast cities.
What it supports
An official source supports the attributed cause for the stated place and dates.
Limit
The NASA collection describes the regional episode and mechanism but does not apportion the individual metro-day measurement.
What remains uncertain
- The NASA collection describes the regional episode and mechanism but does not apportion the individual metro-day measurement.
Status and provenance
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.