Winter inversion
Maryland–Mid-Atlantic 12–15 January stagnation and inversion episode
Daily PM2.5 peaked at 70.5 µg/m³ near Allentown across 4 covered metros home to 4.9 million people.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 2.3 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 12 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
Maryland’s retrospective analysis identifies the 12–15 January episode, including Baltimore, with stagnation and a strong morning inversion, plus a nitrate-rich local component.
Sequence: Baltimore (Jan 13) → Allentown (Jan 14) → Harrisburg (Jan 14) → Scranton (Jan 14)
Affected metros
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| Allentown-Bethlehem-Easton, PA-NJ | 70.5 µg/m³ | 3.2 | Jan 14, 2001 | #12 of its top days |
| Harrisburg-Carlisle, PA | 59.4 µg/m³ | 2.7 | Jan 14, 2001 | #14 of its top days |
| Baltimore-Columbia-Towson, MD | 53.6 µg/m³ | 2.4 | Jan 13, 2001 | #14 of its top days |
| Scranton--Wilkes-Barre--Hazleton, PA | 52.6 µg/m³ | 4.5 | Jan 14, 2001 | #14 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
Agency and publisher pages 1
- Appendix G-1 Maryland’s retrospective episode analysis reports regionwide PM2.5 enhancement on 13 January 2001 and a 12–15 January episode with westerly transport, recirculation, high humidity, stagnation, and a strong morning inversion. It identifies a nitrate-rich local-scale component associated with motor-vehicle and home-heating emissions for the Maryland portion, including Baltimore.
What remains uncertain
- The finding specifically attributes the Maryland portion; supplied evidence does not establish a common source occurrence with the Ohio candidate.
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.