U.S. EPA AirData / Chemical Speciation Network hypothesis
EPA AirData daily_SPEC 2005
Exact-peak-date CSN composition produced secondary-inorganic shares of reconstructed mass as follows: portland 61.3%.
Regional secondary PM Possible
2005-12-09 Portland-Vancouver-Hillsboro, OR-WA regional secondary-particle pollution episode
Daily PM2.5 peaked at 61 µg/m³ near Portland across 1 covered metro home to 2.5 million people.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 2.5 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 6.3 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 “Regional secondary PM”
Exact-peak-date EPA chemical speciation shows secondary inorganic aerosol made up a literal majority of reconstructed PM2.5 mass at every covered affected place.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
National Weather Service via Iowa Environmental Mesonet · Dec 9, 2005 hypothesis
NWS Portland Area Forecast Discussion — December 9, 2005
On the Portland event date, the NWS discussion documented subsidence and surface inversions, capped valleys, and an active air stagnation advisory.
Inference, not direct attribution
Same-day particle composition: EPA speciation observations on the peak date show a majority secondary-inorganic aerosol signature. This supports a regional secondary-particle mechanism, not a single emitting source.
Documented stagnation context: Contemporaneous material documents stagnant conditions in the relevant place and period, but stops short of directly attributing this exact event.
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.
- 1Inferred
Source or mechanism
Pattern-based explanation
Same-day particle composition. EPA speciation observations on the peak date show a majority secondary-inorganic aerosol signature. This supports a regional secondary-particle mechanism, not a single emitting source.
- 2Research gap
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.
- 3Documented
Local response
61 µg/m³ near Portland
EPA monitors recorded the event across 1 metro. The peak daily concentration is roughly 2.8 cigarette-equivalents at the outdoor daily rate.
Inspect the pollutant and weather signals ↓
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 “Regional secondary PM” explanation; it does not assign the cause by itself.
Portland-Vancouver-Hillsboro, OR-WA
Monitor comparison window 2005-12-06 to 2005-12-12 · PM2.5 target: Portland - North Roselawn (PNR)
0% above nearby days
44% lower than surrounding days
59% higher than surrounding days
Pollution fingerprint
Metro-wide median of reporting monitors PM2.5 21.4 µg/m³
About the same as surrounding days
Before13.3 µg/m³ Event21.4 µg/m³ After35.7 µg/m³
Carbon monoxide 0.931 ppm
59% higher than surrounding days
Before0.579 ppm Event0.931 ppm After0.585 ppm
Sulfur dioxide 3.57 ppb
43% higher than surrounding days
Before1.57 ppb Event3.57 ppb After2.50 ppb
Atmospheric conditions
Nearby EPA weather observations6% lower than surrounding days
About the same as surrounding days
About the same as surrounding days
44% 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.
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.
—
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
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.
Affected metros
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| Portland-Vancouver-Hillsboro, OR-WA | 61 µg/m³ | 2.8 | Dec 9, 2005 | #20 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 Portland Area Forecast Discussion — December 9, 2005
National Weather Service via Iowa Environmental Mesonet
On the Portland event date, the NWS discussion documented subsidence and surface inversions, capped valleys, and an active air stagnation advisory.
What it supports
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
Limit
The forecast discussion documents the accumulation meteorology, not the emitting sources or chemical composition.
EPA AirData daily_SPEC 2005
U.S. EPA AirData / Chemical Speciation Network
Exact-peak-date CSN composition produced secondary-inorganic shares of reconstructed mass as follows: portland 61.3%.
What it supports
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
Limit
Composition supports an aerosol mechanism, not an emitting source or named regional episode.
Peak-date reconstructed aerosol composition
U.S. EPA Chemical Speciation Network
On the affected place peak date, reconstructed ammonium sulfate plus ammonium nitrate represented a majority of EPA reconstructed mass at every usable sampled site. portland: median 61% (minimum 61% across 1 site).
What it supports
Measured composition consistent with secondary-inorganic-dominated PM2.5 at sampled monitors on the local peak date.
Limit
A component majority describes aerosol composition at sampled monitors; it does not identify an emitting source.
Secondary-inorganic component majority
IAQng deterministic inference policy
Under csn_secondary_inorganic_majority_on_peak_date.v1, complete affected-place peak-date coverage with a secondary-inorganic majority creates a possible regional-secondary-PM hypothesis.
What it supports
A possible regional secondary PM hypothesis; this is a reproducible inference, not direct source attribution.
Limit
A component majority describes aerosol composition at sampled monitors; it does not identify an emitting source.
What remains uncertain
- A component majority describes aerosol composition at sampled monitors; it does not identify an emitting source.
- CSN samples are intermittent, and absence of a peak-date sample has no negative meaning.
- The 50% threshold is an IAQng catalog convention for a literal majority, not an EPA source-attribution threshold.
- This v1 lead cannot exceed possible confidence and is not promoted when the peak is January 1, July 4-5, or December 31 because fireworks are a competing common-sense pattern requiring separate evidence.
Status and provenance
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.