NASA Earth Observatory · Jun 30, 2003 hypothesis
Haze over the Atlantic Seaboard — June 26, 2003
NASA satellite observations show a broad haze plume over the eastern United States on June 26 and elevated carbon monoxide associated with that haze.
Wildfire smoke Possible
2003-06-26 Baltimore-Columbia-Towson, MD, Harrisburg-Carlisle, PA, and 2 other metros wildfire-smoke episode
Daily PM2.5 peaked at 73.1 µg/m³ near Philadelphia across 4 covered metros home to 16 million people. 4 metros 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 ≈ 2.5 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 41 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 “Wildfire smoke”
NASA observed a thick Atlantic-seaboard haze plume on June 24 that it said might contain Canadian wildfire smoke, then documented persistent haze with elevated carbon monoxide over the eastern United States on June 26. The event's four Mid-Atlantic metros lie inside that same dated regional plume, supporting smoke only as a possible contributor.
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: Philadelphia (Jun 26) → Harrisburg (Jun 26) → Baltimore (Jun 26) → Washington (Jun 26)
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.
- 1Open question
Source or mechanism
Source not directly documented
The catalog has a grouping hypothesis, but no retained source directly establishes the proposed cause.
- 2Documented
Air-mass movement
Transport into the affected region is documented
NASA satellite observations show a broad haze plume over the eastern United States on June 26 and elevated carbon monoxide associated with that haze.
View transport source ↗ - 3Documented
Local response
73.1 µg/m³ near Philadelphia
EPA monitors recorded the event across 4 metros. The peak daily concentration is roughly 3.3 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 “Wildfire smoke” explanation; it does not assign the cause by itself.
Baltimore-Columbia-Towson, MD
Monitor comparison window 2003-06-23 to 2003-06-29 · PM2.5 target: Edgewood
103% above nearby days
No adjacent-day comparison
Pollution fingerprint
Metro-wide median of reporting monitors PM2.5 61.6 µg/m³
103% higher than surrounding days
Before18.8 µg/m³ Event61.6 µg/m³ After30.4 µg/m³
PM10 78 µg/m³
No adjacent-day comparison
Before— Event78 µg/m³ After—
Carbon monoxide 0.477 ppm
About the same as surrounding days
Before0.408 ppm Event0.477 ppm After0.463 ppm
Nitrogen dioxide 25.5 ppb
21% higher than surrounding days
Before27.8 ppb Event25.5 ppb After14.9 ppb
Sulfur dioxide 12.1 ppb
175% higher than surrounding days
Before7.33 ppb Event12.1 ppb After4.29 ppb
Ozone 0.069 ppm
23% higher than surrounding days
Before0.056 ppm Event0.069 ppm After0.054 ppm
Atmospheric conditions
Nearby EPA weather observationsAbout the same as surrounding days
About the same as surrounding days
About the same as surrounding days
Harrisburg-Carlisle, PA
Monitor comparison window 2003-06-23 to 2003-06-29 · PM2.5 target: Harrisburg
126% above nearby days
148% higher than surrounding days
Pollution fingerprint
Metro-wide median of reporting monitors PM2.5 66.7 µg/m³
126% higher than surrounding days
Before17.9 µg/m³ Event66.7 µg/m³ After29.5 µg/m³
PM10 82 µg/m³
148% higher than surrounding days
Before31 µg/m³ Event82 µg/m³ After33 µg/m³
Carbon monoxide 0.700 ppm
25% higher than surrounding days
Before0.563 ppm Event0.700 ppm After0.446 ppm
Nitrogen dioxide 12.2 ppb
19% higher than surrounding days
Before12.8 ppb Event12.2 ppb After7.50 ppb
Sulfur dioxide 12 ppb
360% higher than surrounding days
Before0.896 ppb Event12 ppb After2.60 ppb
Ozone 0.059 ppm
22% higher than surrounding days
Before0.038 ppm Event0.059 ppm After0.048 ppm
Philadelphia-Camden-Wilmington, PA-NJ-DE-MD
Monitor comparison window 2003-06-23 to 2003-06-29 · PM2.5 target: New Garden
129% above nearby days
About the same as surrounding days
115% higher than surrounding days
Pollution fingerprint
Metro-wide median of reporting monitors PM2.5 61.5 µg/m³
129% higher than surrounding days
Before26.8 µg/m³ Event61.5 µg/m³ After26.8 µg/m³
PM10 79.5 µg/m³
115% higher than surrounding days
Before37 µg/m³ Event79.5 µg/m³ After33.5 µg/m³
Carbon monoxide 0.550 ppm
18% higher than surrounding days
Before0.467 ppm Event0.550 ppm After0.425 ppm
Nitrogen dioxide 22.4 ppb
7% higher than surrounding days
Before25.4 ppb Event22.4 ppb After11.7 ppb
Sulfur dioxide 6.98 ppb
56% higher than surrounding days
Before4.48 ppb Event6.98 ppb After3.65 ppb
Ozone 0.084 ppm
39% higher than surrounding days
Before0.061 ppm Event0.084 ppm After0.053 ppm
Atmospheric conditions
Nearby EPA weather observations5% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
Washington-Arlington-Alexandria, DC-VA-MD-WV
Monitor comparison window 2003-06-23 to 2003-06-29 · PM2.5 target: RIVER TERRACE
95% above nearby days
No adjacent-day comparison
Pollution fingerprint
Metro-wide median of reporting monitors PM2.5 54.2 µg/m³
95% higher than surrounding days
Before26.6 µg/m³ Event54.2 µg/m³ After27.8 µg/m³
PM10 55 µg/m³
No adjacent-day comparison
Before— Event55 µg/m³ After—
Carbon monoxide 0.625 ppm
18% higher than surrounding days
Before0.529 ppm Event0.625 ppm After0.425 ppm
Nitrogen dioxide 20.5 ppb
7% higher than surrounding days
Before22.7 ppb Event20.5 ppb After16.3 ppb
Sulfur dioxide 9.63 ppb
8% higher than surrounding days
Before10.5 ppb Event9.63 ppb After4.46 ppb
Ozone 0.060 ppm
22% higher than surrounding days
Before0.052 ppm Event0.060 ppm After0.049 ppm
Atmospheric conditions
Nearby EPA weather observationsAbout the same as surrounding days
6% higher 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.
Air-mass reconstruction
Where the air had been
NOAA HYSPLIT traces the air arriving at each metro backward for 72 hours. Multiple arrival times and heights show whether the broad path is stable—or sensitive to assumptions about when and where the polluted layer arrived.
Air arriving near Baltimore-Columbia-Towson
Peak-date arrivals · 2003-06-26
Broad history Mostly west of the metro
72-hour reach 550–850 km
Sensitivity runs 12 modeled paths
Near surface · 100 mLower atmosphere · 500 mHigher layer · 1,000 m
Each line begins 72 hours before arrival and points toward the metro. Color represents arrival height; repeated lines represent 00, 06, 12, and 18 UTC arrival assumptions. A path can show where the air traveled, but it cannot prove which source added the PM2.5.
Air arriving near Harrisburg-Carlisle
Peak-date arrivals · 2003-06-26
Broad history Mostly west of the metro
72-hour reach 550–950 km
Sensitivity runs 12 modeled paths
Near surface · 100 mLower atmosphere · 500 mHigher layer · 1,000 m
Each line begins 72 hours before arrival and points toward the metro. Color represents arrival height; repeated lines represent 00, 06, 12, and 18 UTC arrival assumptions. A path can show where the air traveled, but it cannot prove which source added the PM2.5.
Air arriving near Philadelphia-Camden-Wilmington
Peak-date arrivals · 2003-06-26
Broad history Mostly west of the metro
72-hour reach 650–1,000 km
Sensitivity runs 12 modeled paths
Near surface · 100 mLower atmosphere · 500 mHigher layer · 1,000 m
Each line begins 72 hours before arrival and points toward the metro. Color represents arrival height; repeated lines represent 00, 06, 12, and 18 UTC arrival assumptions. A path can show where the air traveled, but it cannot prove which source added the PM2.5.
Air arriving near Washington-Arlington-Alexandria
Peak-date arrivals · 2003-06-26
Broad history Mostly west of the metro
72-hour reach 450–750 km
Sensitivity runs 12 modeled paths
Near surface · 100 mLower atmosphere · 500 mHigher layer · 1,000 m
Each line begins 72 hours before arrival and points toward the metro. Color represents arrival height; repeated lines represent 00, 06, 12, and 18 UTC arrival assumptions. A path can show where the air traveled, but it cannot prove which source added the PM2.5.
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 |
|---|---|---|---|---|
| Philadelphia-Camden-Wilmington, PA-NJ-DE-MD | 73.1 µg/m³ | 3.3 | Jun 26, 2003 | #10 of its top days |
| Harrisburg-Carlisle, PA | 70.9 µg/m³ | 3.2 | Jun 26, 2003 | #9 of its top days |
| Baltimore-Columbia-Towson, MD | 68.7 µg/m³ | 3.1 | Jun 26, 2003 | #6 of its top days |
| Washington-Arlington-Alexandria, DC-VA-MD-WV | 61.9 µg/m³ | 2.8 | Jun 26, 2003 | #10 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 Atlantic Seaboard — June 26, 2003
NASA Earth Observatory
NASA satellite observations show a broad haze plume over the eastern United States on June 26 and elevated carbon monoxide associated with that haze.
What it supports
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
Limit
This page confirms the dated plume and pollution but does not itself identify the aerosol source.
Haze over the Atlantic Seaboard
NASA Earth Observatory
NASA observed thick East Coast haze on June 24 and said Canadian-fire smoke was a possibility.
What it supports
Context for the event; this item does not establish the attributed cause by itself.
Limit
The image precedes the event by two days and NASA's wildfire language is qualified.
What remains uncertain
- NASA's wildfire language is explicitly qualified, so this remains a possible smoke contribution rather than a verified smoke attribution.
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.