NASA Earth Observatory corroborates
Haze over the United States
NASA says particle pollution lingered over the Mississippi Valley and Deep South from June 20, 2005, with haze-laden air transported from the Ohio Valley and Upper Midwest.
Regional secondary PM Possible
2005-06-25 Nashville-Davidson--Murfreesboro--Franklin, TN regional secondary-particle pollution episode
Daily PM2.5 peaked at 46.5 µg/m³ near Nashville across 1 covered metro home to 2.2 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 ≈ 1.6 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 3.5 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 “Regional secondary PM”
NASA documented a persistent June 20 onward haze episode over the Mississippi Valley and Deep South, with polluted air transported from the Ohio Valley and Upper Midwest. The evidence is regional rather than Nashville-specific.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
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
Regional secondary PM
NASA says particle pollution lingered over the Mississippi Valley and Deep South from June 20, 2005, with haze-laden air transported from the Ohio Valley and Upper Midwest.
View supporting source ↗ - 2Documented
Air-mass movement
Transport into the affected region is documented
NASA says particle pollution lingered over the Mississippi Valley and Deep South from June 20, 2005, with haze-laden air transported from the Ohio Valley and Upper Midwest.
View transport source ↗ - 3Documented
Local response
46.5 µg/m³ near Nashville
EPA monitors recorded the event across 1 metro. The peak daily concentration is roughly 2.1 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 “Regional secondary PM” explanation; it does not assign the cause by itself.
Nashville-Davidson--Murfreesboro--Franklin, TN
Monitor comparison window 2005-06-22 to 2005-06-28 · PM2.5 target: Lockeland
67% above nearby days
13% higher than surrounding days
Pollution fingerprint
Metro-wide median of reporting monitors PM2.5 46.5 µg/m³
67% higher than surrounding days
Before27.9 µg/m³ Event46.5 µg/m³ After19.5 µg/m³
Carbon monoxide 0.881 ppm
13% higher than surrounding days
Before0.727 ppm Event0.881 ppm After0.854 ppm
Nitrogen dioxide 26.8 ppb
27% higher than surrounding days
Before24.4 ppb Event26.8 ppb After19.8 ppb
Sulfur dioxide 3.92 ppb
About the same as surrounding days
Before4.08 ppb Event3.92 ppb After2.75 ppb
Ozone 0.051 ppm
12% higher than surrounding days
Before0.049 ppm Event0.051 ppm After0.030 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.
—
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 |
|---|---|---|---|---|
| Nashville-Davidson--Murfreesboro--Franklin, TN | 46.5 µg/m³ | 2.1 | Jun 25, 2005 | #9 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 United States
NASA Earth Observatory
NASA says particle pollution lingered over the Mississippi Valley and Deep South from June 20, 2005, with haze-laden air transported from the Ohio Valley and Upper Midwest.
What it supports
A retained source supports the attributed cause for the stated place and dates.
What remains uncertain
- The retained evidence is scoped to the places and dates stated; it is not a catalog promotion.
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.