Stagnant pollution mixture Possible
Daily PM2.5 peaked at 50.2 µg/m³ near Boston across 3 covered metros home to 7.9 million people.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 1.8 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 14 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
EPA's exact-window regional alert documents elevated particles during hot weather, while EPA's annual assessment says warm, dry summer conditions and photochemical transport favored higher fine-particle concentrations in southern New England. Together they support a stagnant transported pollution mixture at possible confidence.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
U.S. EPA Region 1 · Jun 26, 2007 hypothesis
EPA forecast elevated particle pollution across Massachusetts, Rhode Island, and Connecticut on June 27, 2007 during hot weather and high electrical demand.
See every retained source and limitation ↓
Sequence: Boston (Jun 27) → Hartford (Jun 27) → Providence (Jun 27)
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
The catalog has a grouping hypothesis, but no retained source directly establishes the proposed cause.
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 3 metros. The peak daily concentration is roughly 2.3 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 “Stagnant pollution mixture” explanation; it does not assign the cause by itself.
Boston-Cambridge-Newton, MA-NH
Monitor comparison window 2007-06-24 to 2007-06-30 · PM2.5 target: DUDLEY SQUARE ROXBURY
163% above nearby days
8% higher than surrounding days
163% higher than surrounding days
8% higher than surrounding days
8% higher than surrounding days
98% higher than surrounding days
84% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
11% higher than surrounding days
Hartford-West Hartford-East Hartford, CT
Monitor comparison window 2007-06-24 to 2007-06-30 · PM2.5 target: McAuliffe Park
152% above nearby days
52% higher than surrounding days
152% higher than surrounding days
52% higher than surrounding days
54% higher than surrounding days
912% higher than surrounding days
79% higher than surrounding days
17% higher than surrounding days
About the same as surrounding days
9% higher than surrounding days
Providence-Warwick, RI-MA
Monitor comparison window 2007-06-24 to 2007-06-30 · PM2.5 target: FALL RIVER
157% above nearby days
33% higher than surrounding days
157% higher than surrounding days
33% higher than surrounding days
8% higher than surrounding days
180% higher than surrounding days
13% higher than surrounding days
9% higher than surrounding days
About the same as surrounding days
9% 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.
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 |
|---|---|---|---|---|
| Boston-Cambridge-Newton, MA-NH | 50.2 µg/m³ | 2.3 | Jun 27, 2007 | #14 of its top days |
| Hartford-West Hartford-East Hartford, CT | 45.8 µg/m³ | 2.1 | Jun 27, 2007 | #16 of its top days |
| Providence-Warwick, RI-MA | 43.7 µg/m³ | 2.0 | Jun 27, 2007 | #17 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.
U.S. EPA Region 1
EPA reports that 2007's warm, dry summer favored elevated southern New England fine particles and explains that haze in the region is influenced by photochemical formation and transport mechanisms.
Context for the event; this item does not establish the attributed cause by itself.
The annual report describes the seasonal mechanism and regional pattern rather than a dedicated June 27 source-apportionment analysis.
U.S. EPA Region 1
EPA forecast elevated particle pollution across Massachusetts, Rhode Island, and Connecticut on June 27, 2007 during hot weather and high electrical demand.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
EPA's listed PM source categories are generic and do not attribute this specific episode.
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.