NASA Earth Observatory corroborates
Code Red Air over the Mid-Atlantic States
NASA observed an eastern U.S. aerosol shroud on June 28 amid June 26-29 advisories and described a possible mixture of pollution, smoke, and cirrus.
Mixed causes Possible
2001-06-29 to 2001-06-30 Baltimore-Columbia-Towson, MD, New York-Newark-Jersey City, NY-NJ-PA, and 1 other metros mixed-source pollution episode
Daily PM2.5 peaked at 62.1 µg/m³ near Baltimore across 3 covered metros home to 23 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 ≈ 46 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 “Mixed causes”
NASA's same-window satellite narrative identifies the eastern aerosol shroud as a possible mixture of pollution and smoke while documenting poor-air advisories in the affected Mid-Atlantic corridor. That supports a mixed-aerosol hypothesis at possible confidence, not a unique source attribution.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
NASA Earth Observatory · Jun 30, 2001 corroborates
Code Red Air over the Mid-Atlantic States
NASA documented a regional aerosol shroud over parts of Pennsylvania, Maryland, and Virginia on June 28 and reported poor-air-quality advisories in Baltimore and Washington from June 26-29. It supports a regional late-June air-pollution episode but explicitly describes the aerosol composition as uncertain and does not attribute individual PM2.5 monitors.
See every retained source and limitation ↓
Sequence: Baltimore (Jun 29) → Scranton (Jun 29) → New York (Jun 30)
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
Mixed causes
NASA observed an eastern U.S. aerosol shroud on June 28 amid June 26-29 advisories and described a possible mixture of pollution, smoke, and cirrus.
View supporting source ↗ - 2Documented
Air-mass movement
Transport into the affected region is documented
NASA observed an eastern U.S. aerosol shroud on June 28 amid June 26-29 advisories and described a possible mixture of pollution, smoke, and cirrus.
View transport source ↗ - 3Documented
Local response
62.1 µg/m³ near Baltimore
EPA monitors recorded the event across 3 metros. The peak daily concentration is roughly 2.8 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 “Mixed causes” explanation; it does not assign the cause by itself.
Baltimore-Columbia-Towson, MD
Monitor comparison window 2001-06-26 to 2001-07-03 · PM2.5 target: Oldtown
44% above nearby days
No adjacent-day comparison
Pollution fingerprint
Metro-wide median of reporting monitors PM2.5 46 µg/m³
44% higher than surrounding days
Before32.6 µg/m³ Event46 µg/m³ After13.3 µg/m³
PM10 41 µg/m³
No adjacent-day comparison
Before— Event41 µg/m³ After—
Carbon monoxide 0.233 ppm
5% lower than surrounding days
Before0.248 ppm Event0.233 ppm After0.246 ppm
Nitrogen dioxide 23.8 ppb
21% higher than surrounding days
Before21.1 ppb Event23.8 ppb After11.6 ppb
Sulfur dioxide 2.52 ppb
35% lower than surrounding days
Before6.71 ppb Event2.52 ppb After3.88 ppb
Ozone 0.055 ppm
About the same as surrounding days
Before0.064 ppm Event0.055 ppm After0.039 ppm
Atmospheric conditions
Nearby EPA weather observations9% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
Scranton--Wilkes-Barre--Hazleton, PA
Monitor comparison window 2001-06-26 to 2001-07-03 · PM2.5 target: Scranton
61% above nearby days
62% higher than surrounding days
Pollution fingerprint
Metro-wide median of reporting monitors PM2.5 44.3 µg/m³
61% higher than surrounding days
Before36.8 µg/m³ Event44.3 µg/m³ After12.1 µg/m³
PM10 56.8 µg/m³
62% higher than surrounding days
Before47.5 µg/m³ Event56.8 µg/m³ After19.5 µg/m³
Carbon monoxide 0.553 ppm
10% higher than surrounding days
Before0.512 ppm Event0.553 ppm After0.398 ppm
Nitrogen dioxide 15 ppb
15% higher than surrounding days
Before18.1 ppb Event15 ppb After6.29 ppb
Sulfur dioxide 8.52 ppb
94% higher than surrounding days
Before3.13 ppb Event8.52 ppb After3.18 ppb
Ozone 0.057 ppm
37% higher than surrounding days
Before0.038 ppm Event0.057 ppm After0.034 ppm
New York-Newark-Jersey City, NY-NJ-PA
Monitor comparison window 2001-06-26 to 2001-07-03 · PM2.5 target: New Brunswick
54% above nearby days
11% lower than surrounding days
No adjacent-day comparison
Pollution fingerprint
Metro-wide median of reporting monitors PM2.5 30.2 µg/m³
54% higher than surrounding days
Before28.8 µg/m³ Event30.2 µg/m³ After8.60 µg/m³
PM10 63 µg/m³
No adjacent-day comparison
Before— Event63 µg/m³ After—
Carbon monoxide 0.873 ppm
10% higher than surrounding days
Before0.817 ppm Event0.873 ppm After0.579 ppm
Nitrogen dioxide 21.6 ppb
About the same as surrounding days
Before30.9 ppb Event21.6 ppb After15.3 ppb
Sulfur dioxide 5.21 ppb
19% higher than surrounding days
Before5 ppb Event5.21 ppb After2.75 ppb
Ozone 0.054 ppm
16% higher than surrounding days
Before0.056 ppm Event0.054 ppm After0.041 ppm
Atmospheric conditions
Nearby EPA weather observationsAbout the same as surrounding days
About the same as surrounding days
About the same as surrounding days
11% 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 |
|---|---|---|---|---|
| Baltimore-Columbia-Towson, MD | 62.1 µg/m³ | 2.8 | Jun 29, 2001 | #9 of its top days |
| New York-Newark-Jersey City, NY-NJ-PA | 54.2 µg/m³ | 2.5 | Jun 30, 2001 | #21 of its top days |
| Scranton--Wilkes-Barre--Hazleton, PA | 49.3 µg/m³ | 2.2 | Jun 29, 2001 | #19 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.
Code Red Air over the Mid-Atlantic States
NASA Earth Observatory
NASA observed an eastern U.S. aerosol shroud on June 28 amid June 26-29 advisories and described a possible mixture of pollution, smoke, and cirrus.
What it supports
A retained source supports the attributed cause for the stated place and dates.
Limit
NASA describes the aerosol as a possible mixture and includes cirrus as an image-interpretation alternative; it does not quantify the pollution and smoke fractions.
What remains uncertain
- The cause remains possible because the official narrative does not distinguish a dominant source or provide surface composition for every metro.
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.