Regional secondary PM Possible
Daily PM2.5 peaked at 46.9 µg/m³ near Boston across 1 covered metro home to 5.0 million people.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 1.7 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 8.5 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
A peer-reviewed satellite, reanalysis, surface-monitor, and WRF-Chem study identifies June 26-28, 2005 as one of six regional-scale eastern U.S. extreme aerosol events selected specifically after excluding biomass burning and wind-blown dust. The authors find the selected events were dominated by anthropogenic sulfate. Boston's same-day PM2.5 peak can therefore be described as possibly part of that regional secondary-particle episode, but the study's event centroid was in the Midwest and no Boston source fraction is reported.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
Journal of Geophysical Research: Atmospheres · Apr 1, 2021 corroborates
The study identifies June 26-28, 2005 as a regional-scale extreme aerosol event over the eastern United States. Its screening excluded biomass-burning and wind-blown-dust cases, and its reanalysis, observations, and WRF-Chem results indicate that the selected events were dominated by anthropogenic sulfate.
Inference, not direct attribution
modeled_anthropogenic_sulfate_event_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
The study identifies June 26-28, 2005 as a regional-scale extreme aerosol event over the eastern United States. Its screening excluded biomass-burning and wind-blown-dust cases, and its reanalysis, observations, and WRF-Chem results indicate that…
View supporting source ↗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 2.1 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 “Regional secondary PM” explanation; it does not assign the cause by itself.
Boston-Cambridge-Newton, MA-NH
Monitor comparison window 2005-06-23 to 2005-06-29 · PM2.5 target: NORTH END SITE CENTRAL ARTERY
89% above nearby days
4 calm hours observed
Haze reported during 19 hours
89% higher than surrounding days
49% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
63% higher than surrounding days
12 kt maximum · 4 of 24 observed hours calm
6 observed hours at or below 3 miles
68°F to 90°F
87% 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 |
|---|---|---|---|---|
| Boston-Cambridge-Newton, MA-NH | 46.9 µg/m³ | 2.1 | Jun 26, 2005 | #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.
Journal of Geophysical Research: Atmospheres
The study identifies June 26-28, 2005 as a regional-scale extreme aerosol event over the eastern United States. Its screening excluded biomass-burning and wind-blown-dust cases, and its reanalysis, observations, and WRF-Chem results indicate that the selected events were dominated by anthropogenic sulfate.
A retained source supports the attributed cause for the stated place and dates.
The June 2005 event centroid was in the Midwest, and the paper does not apportion Boston's daily PM2.5 value.
Journal of Geophysical Research: Atmospheres
The study identifies June 26-28, 2005 as an extreme aerosol event with widespread coincident high near-surface PM2.5, but centers the event in the Midwest.
Context for the event; this item does not establish the attributed cause by itself.
The paper does not directly attribute Boston's daily peak or provide a Boston-specific cause.
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.