Regional secondary PM Possible
Daily PM2.5 peaked at 77.7 µg/m³ near New York across 1 covered metro home to 20 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 ≈ 5.4 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 107 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
EPA's PMF appendix contains an actual Bronx sample on New York's October 27, 2000 peak date. Ammonium nitrate was the largest modeled factor, and EPA describes that factor as a regional nitrate signature. Together with the already retained exact-window ridge, haze, and broad multi-monitor particle episode, this supports regional secondary-particle pollution at possible confidence for New York only.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
National Weather Service surface observations via Iowa Environmental Mesonet · Oct 26, 2000 hypothesis
Newark's official surface station recorded ten hours of haze, 27 hours of mist, and visibility at or below five miles during half of the event hours; 56.3% of hours had wind at or below three knots.
U.S. Environmental Protection Agency · Sep 24, 2003 hypothesis
EPA's Positive Matrix Factorization time series includes an actual sample at site 36-005-0083 on 2000-10-27; ammonium nitrate was the largest modeled factor on the event's peak date, with smaller industrial, mobile, oil, and coal factors.
National Weather Service New York via Iowa Environmental Mesonet · Oct 26, 2000 hypothesis
The exact-window NWS discussion described persistent high pressure and ridging, light easterly flow, and widespread dense fog across the New York forecast area.
Inference, not direct attribution
epa_pmf_exact_sample_factor_pattern.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
epa_pmf_exact_sample_factor_pattern.v1. This inference is recorded in the catalog methodology.
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 3.5 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.
New York-Newark-Jersey City, NY-NJ-PA
Monitor comparison window 2000-10-23 to 2000-10-30 · PM2.5 target: Elizabeth Lab
301% above nearby days
21% lower than surrounding days
108% higher than surrounding days
301% higher than surrounding days
108% higher than surrounding days
121% higher than surrounding days
51% higher than surrounding days
50% higher than surrounding days
27% lower than surrounding days
20% higher than surrounding days
About the same as surrounding days
8% higher than surrounding days
21% lower 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 |
|---|---|---|---|---|
| New York-Newark-Jersey City, NY-NJ-PA | 77.7 µg/m³ | 6.4 | Oct 27, 2000 | #6 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. Environmental Protection Agency
EPA's Positive Matrix Factorization time series includes an actual sample at site 36-005-0083 on 2000-10-27; ammonium nitrate was the largest modeled factor on the event's peak date, with smaller industrial, mobile, oil, and coal factors.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The appendix reports modeled factor contributions at one chemical-speciation monitor, not the complete metro-wide emissions inventory.
U.S. Environmental Protection Agency
EPA identifies the Bronx ammonium-nitrate factor as a regional nitrate signature and the coal factor as regional background and transport. The report documents the site's modeled date range, factor interpretation, average apportioned mass, local source setting, and back-trajectory context.
Context for the event; this item does not establish the attributed cause by itself.
The site summary defines and contextualizes the factors across the modeled period; the separate appendix supplies the event-date source strengths.
National Weather Service surface observations via Iowa Environmental Mesonet
Newark's official surface station recorded ten hours of haze, 27 hours of mist, and visibility at or below five miles during half of the event hours; 56.3% of hours had wind at or below three knots.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The Newark station is one part of a very large metro, and fog or haze does not identify particle composition.
National Weather Service New York via Iowa Environmental Mesonet
The exact-window NWS discussion described persistent high pressure and ridging, light easterly flow, and widespread dense fog across the New York forecast area.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The discussion supports weak ventilation but does not identify the particle source or composition.
U.S. EPA AirData
EPA records show median daily PM2.5 of 56.3 micrograms per cubic meter across 34 monitors, more than six times the adjacent-window level, with compatible PM10, carbon monoxide, nitrogen dioxide, and sulfur dioxide increases.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The fingerprint demonstrates a broad mixed-pollutant episode but cannot apportion individual sources.
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.