Regional secondary PM Possible
Daily PM2.5 peaked at 78.4 µg/m³ near Springfield across 4 covered metros home to 6.9 million people. 1 metro recorded their worst day on record; 3 placed a top-ten day.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 2.4 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 17 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 government episode analysis documents a July 1-3, 2002 regional high-pollution episode in which high pressure, transported pollution, and a haze layer moved northeast into New England. The analysis is ozone-centered and does not apportion PM2.5, so regional secondary particles remain a possible mechanism rather than a direct attribution.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
U.S. EPA Regulations.gov docket attachment corroborates
The government episode analysis describes July 1-3, 2002 as a regional high-pollution event under high pressure and tracks a transported haze layer northeast into New England during the supplied window.
Inference, not direct attribution
regional_haze_secondary_pm_possible.v1: This inference is recorded in the catalog methodology.
See every retained source and limitation ↓
Sequence: Springfield (Jul 1) → Boston (Jul 1) → New Haven (Jul 2) → Worcester (Jul 2)
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 government episode analysis describes July 1-3, 2002 as a regional high-pollution event under high pressure and tracks a transported haze layer northeast into New England during the supplied window.
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 4 metros. The peak daily concentration is roughly 3.6 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 2002-06-28 to 2002-07-05
35% above nearby days
20% lower than surrounding days
35% higher than surrounding days
20% lower than surrounding days
61% higher than surrounding days
29% higher than surrounding days
About the same as surrounding days
18% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
5% higher than surrounding days
Springfield, MA
Monitor comparison window 2002-06-28 to 2002-07-05 · PM2.5 target: LIBERTY ST PARKING LOT
53% above nearby days
No adjacent-day comparison
53% higher than surrounding days
No adjacent-day comparison
28% higher than surrounding days
31% higher than surrounding days
57% higher than surrounding days
22% higher than surrounding days
12% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
New Haven-Milford, CT
Monitor comparison window 2002-06-28 to 2002-07-05
115% above nearby days
62% higher than surrounding days
115% higher than surrounding days
62% higher than surrounding days
31% higher than surrounding days
55% higher than surrounding days
95% higher than surrounding days
21% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
Worcester, MA-CT
Monitor comparison window 2002-06-28 to 2002-07-05
48% above nearby days
No adjacent-day comparison
48% higher than surrounding days
No adjacent-day comparison
17% higher than surrounding days
About the same as surrounding days
67% higher than surrounding days
31% higher than surrounding days
5% 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 |
|---|---|---|---|---|
| Springfield, MA | 78.4 µg/m³ | 3.6 | Jul 1, 2002 | Worst day on record |
| Boston-Cambridge-Newton, MA-NH | 66.9 µg/m³ | 3.0 | Jul 1, 2002 | #3 of its top days |
| New Haven-Milford, CT | 54.1 µg/m³ | 2.5 | Jul 2, 2002 | #10 of its top days |
| Worcester, MA-CT | 39.2 µg/m³ | 1.8 | Jul 2, 2002 | #18 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 Regulations.gov docket attachment
The government episode analysis describes July 1-3, 2002 as a regional high-pollution event under high pressure and tracks a transported haze layer northeast into New England during the supplied window.
A retained source supports the attributed cause for the stated place and dates.
The document analyzes ozone and regional haze; it does not chemically apportion PM2.5 at the four supplied metros.
Massachusetts Department of Environmental Protection
Massachusetts' annual report independently records the July 1-3 regional pollution episode in the state monitoring record.
Context for the event; this item does not establish the attributed cause by itself.
The annual report corroborates the episode dates but is not a PM2.5 source-apportionment study.
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.