Mixed causes Possible
Daily PM2.5 peaked at 69.3 µg/m³ near Allentown across 1 covered metro home to 886,418 people.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 2.7 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 2.4 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
NASA documented a broad carbon-monoxide-associated haze pall over the eastern United States on June 26. Allentown simultaneously recorded a sharp three-monitor PM2.5 rise with PM10, nitrogen dioxide, and sulfur dioxide, while Pennsylvania documented nearby same-day ozone exceedances. The evidence supports a regional mixed-pollution episode but cannot identify a unique source or quantify the local PM2.5 fractions.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
U.S. EPA AirData hypothesis
EPA records show median daily PM2.5 of 65.9 micrograms per cubic meter across 3 monitors, 2.434 times the adjacent-window level. Co-pollutants at least 10% above the adjacent-window comparison were pm10 (2.15x), carbon monoxide (1.247x), nitrogen dioxide (1.151x), sulfur dioxide (2.582x).
National Weather Service surface observations via Iowa Environmental Mesonet · Jun 26, 2003 hypothesis
ALLENTOWN-BETHLEHEM recorded calm conditions during 17% of event hours and wind at or below three knots during 29%. Observations included 7 haze hours, 4 mist hours, minimum visibility 3 miles.
NASA Earth Observatory · Jun 30, 2003 hypothesis
NASA's Terra satellite observed a broad pall of haze across the eastern United States on June 26, 2003, with MOPITT observations confirming high carbon monoxide values associated with the haze.
Inference, not direct attribution
documented_regional_combustion_haze_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_regional_combustion_haze_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 3.1 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 “Mixed causes” explanation; it does not assign the cause by itself.
Allentown-Bethlehem-Easton, PA-NJ
Monitor comparison window 2003-06-23 to 2003-06-29 · PM2.5 target: Freemansburg
106% above nearby days
4 calm hours observed
Haze reported during 7 hours
106% higher than surrounding days
105% higher than surrounding days
About the same as surrounding days
18% higher than surrounding days
92% higher than surrounding days
38% higher than surrounding days
9 kt maximum · 4 of 24 observed hours calm
1 observed hours at or below 3 miles
69°F to 93°F
93% maximum
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 |
|---|---|---|---|---|
| Allentown-Bethlehem-Easton, PA-NJ | 69.3 µg/m³ | 3.1 | Jun 26, 2003 | #13 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.
NASA Earth Observatory
NASA's Terra satellite observed a broad pall of haze across the eastern United States on June 26, 2003, with MOPITT observations confirming high carbon monoxide values associated with the haze.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The satellite record documents the regional haze and carbon monoxide but does not apportion Allentown's PM2.5 mass.
National Weather Service surface observations via Iowa Environmental Mesonet
ALLENTOWN-BETHLEHEM recorded calm conditions during 17% of event hours and wind at or below three knots during 29%. Observations included 7 haze hours, 4 mist hours, minimum visibility 3 miles.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
A single surface station documents weak ventilation and obscuration but not the full vertical profile or particle source mix.
Pennsylvania Department of Environmental Protection
Pennsylvania's annual report lists one-hour ozone exceedances at Reading and Lancaster on June 26, corroborating a regional photochemical-pollution episode in eastern Pennsylvania on the exact date of the Allentown particle spike.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The listed ozone monitors are outside Allentown, and ozone corroborates a regional polluted air mass but does not determine Allentown PM2.5 composition.
U.S. EPA AirData
EPA records show median daily PM2.5 of 65.9 micrograms per cubic meter across 3 monitors, 2.434 times the adjacent-window level. Co-pollutants at least 10% above the adjacent-window comparison were pm10 (2.15x), carbon monoxide (1.247x), nitrogen dioxide (1.151x), sulfur dioxide (2.582x).
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The broad multi-pollutant response does not apportion traffic, heating, industry, wood combustion, or secondary aerosol.
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.