Winter inversion
2010-12-31 through 2011-01-01 winter-inversion episode affecting Bridgeport-Stamford-Norwalk, CT, Springfield, MA, Allentown-Bethlehem-Easton, PA-NJ
Daily PM2.5 peaked at 57.5 µg/m³ near Bridgeport across 3 covered metros home to 2.3 million people. 1 metro 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 ≈ 2.8 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 6.6 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.
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.
What happened, in the record
The frozen records support a December 31-January 1 Connecticut River Valley particle-pollution episode, and the contemporaneous alert attributes the Springfield portion to inversion or stagnant conditions trapping pollution. This supports winter inversion as the broad cause, while Allentown remains unassessed.
Sequence: Bridgeport (Dec 31) → Springfield (Dec 31) → Allentown (Jan 1)
Affected metros
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| Bridgeport-Stamford-Norwalk, CT | 57.5 µg/m³ | 4.9 | Jan 1, 2011 | #9 of its top days |
| Allentown-Bethlehem-Easton, PA-NJ | 53.2 µg/m³ | 2.4 | Jan 1, 2011 | #25 of its top days |
| Springfield, MA | 44.5 µg/m³ | 2.0 | Dec 31, 2010 | #25 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.
The evidence
NWS Air Quality Alert 1
- Air Quality Alert AQABOX An archived NWS Air Quality Alert for Springfield, MA, issued 2010-12-31T21:15Z, explicitly identifies an inversion or stagnant conditions trapping particle pollution. IEM is the archive, not the official system of record.
Agency and publisher pages 1
- 12/30/2010: Poor Air Quality Predicted in Connecticut and in Valley Areas of Massachusetts, New Hampshire, and Vermont EPA forecast poor fine-particle air quality for December 31 across Connecticut and the Connecticut River Valley including Springfield, Massachusetts, with improvement expected after a cold front increased wind speeds. It supports grouping the Connecticut and Springfield portions of this event, but does not attribute a specific emissions source or address Allentown.
What remains uncertain
- The inversion attribution directly covers Springfield and the official regional forecast covers Connecticut, but the supplied evidence does not assess Allentown.
- The retained archive is corroborative rather than the official system of record.
Status and provenance
Research preview: this record carries research-only status and its boundaries, cause, and name may change as evidence review completes. Grouping policy common_sense_root_cause_grouping.v2. The cause label reflects the assembled evidence above, not an IAQng detection formula.