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Winter inversion Agency determination

2010-12-31 through 2011-01-01 winter-inversion episode affecting Bridgeport-Stamford-Norwalk, CT, Springfield, MA, Allentown-Bethlehem-Easton, PA-NJ

December 31, 2010 to January 1, 2011

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.

Why we think this happened

The basis for “Winter inversion”

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.

Agency determination A government body issued a record naming this cause for this event: an NWS air-quality alert, a NOAA Storm Events record, or a state or local official archive.

U.S. Environmental Protection Agency · Dec 30, 2010 official

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.

National Weather Service via Iowa Environmental Mesonet archive · Dec 31, 2010 corroborates

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.

See every retained source and limitation ↓

Sequence: Bridgeport (Dec 31) → Springfield (Dec 31) → Allentown (Jan 1)

Evidence path

From source to city

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.

Open the evidence ledger ↓
  1. 1

    Source or mechanism

    Winter inversion

    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.

    View supporting source ↗
    Documented
  2. 2

    Air-mass movement

    The transport path has not been reconstructed

    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.

    Research gap
  3. 3

    Local response

    57.5 µg/m³ near Bridgeport

    EPA monitors recorded the event across 3 metros. The peak daily concentration is roughly 2.6 cigarette-equivalents at the outdoor daily rate.

    Inspect the pollutant and weather signals ↓
    Documented

Event autopsy

What the instruments saw

Before, during, and after the episode: nearby pollutant monitors and surface-weather stations show what changed. This context tests the “Winter inversion” explanation; it does not assign the cause by itself.

Observed context · not attribution

Bridgeport-Stamford-Norwalk, CT

Monitor comparison window 2010-12-28 to 2011-01-04 · PM2.5 target: Sherwood Island Connector

4 pollutant signals
Fine-particle pulse 50 µg/m³

83% above nearby days

Carbon monoxide 1.01 ppm

81% higher than surrounding days

Pollution fingerprint

Metro-wide median of reporting monitors
PM2.5 50 µg/m³

83% higher than surrounding days

Before12.7 µg/m³ Event50 µg/m³ After18.5 µg/m³
4 monitors · 24 HOUR
Carbon monoxide 1.01 ppm

81% higher than surrounding days

Before0.322 ppm Event1.01 ppm After0.553 ppm
2 monitors · 1 HOUR
Nitrogen dioxide 42.7 ppb

55% higher than surrounding days

Before18.3 ppb Event42.7 ppb After22.4 ppb
1 monitor · 1 HOUR
Sulfur dioxide 11.7 ppb

97% higher than surrounding days

Before3.36 ppb Event11.7 ppb After3.69 ppb
2 monitors · 1 HOUR

Atmospheric conditions

Nearby EPA weather observations
Humidity 33.6 °F

27% higher than surrounding days

Temperature 39.6 °F

17% 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.

Measured daily PM2.5 at EPA monitors, as cigarette-equivalents
EPA monitors sit in metro areas, so the colour clusters there. Land between and beyond them is unmeasured, not clean: this map shows where IAQng has readings, not the extent of the smoke.
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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

Camera views near

Browse the camera map →

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.

Affected metros

MetroPeak PM2.5Cigarettes, whole eventPeak dayAll-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.

Public evidence library

What supports this account

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.

NWS Air Quality Alert 1

  • Air Quality Alert AQABOX

    National Weather Service via Iowa Environmental Mesonet archive · Dec 31, 2010 corroborates government

    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

What remains uncertain

Status and provenance

Agency determination A government body issued a record naming this cause for this event: an NWS air-quality alert, a NOAA Storm Events record, or a state or local official archive.

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.