Where the Heck Is Mom · May 4, 2009 corroborates
April-May 2009 Honolulu journal
A contemporaneous Honolulu account says vog from the Big Island was making the air look and feel poor during the exact period.
Other Possible
2009-05-04 Urban Honolulu, HI other documented pollution episode
Daily PM2.5 peaked at 23.1 µg/m³ near Urban Honolulu across 1 covered metro home to 998,747 people.
Why we think this happened
The basis for “Other”
A contemporaneous Honolulu community account explicitly describes vog degrading the air in the exact period, but it is not an official monitor attribution.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
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.
- 1Documented
Source or mechanism
Other
A contemporaneous Honolulu account says vog from the Big Island was making the air look and feel poor during the exact period.
View supporting source ↗ - 2Modeled
Air-mass movement
The 72-hour air-mass history is reconstructed
NOAA HYSPLIT modeled 12 backward paths across multiple arrival times and heights. They show where the air traveled, not which source polluted it.
Explore the modeled paths ↓ - 3Documented
Local response
23.1 µg/m³ near Urban Honolulu
EPA monitors recorded the event across 1 metro. The peak daily concentration is roughly 1.1 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 “Other” explanation; it does not assign the cause by itself.
Urban Honolulu, HI
Monitor comparison window 2009-05-01 to 2009-05-07 · PM2.5 target: Kapolei
119% above nearby days
56% higher than surrounding days
Pollution fingerprint
Metro-wide median of reporting monitors PM2.5 21 µg/m³
119% higher than surrounding days
Before5.63 µg/m³ Event21 µg/m³ After11.9 µg/m³
PM10 33.5 µg/m³
56% higher than surrounding days
Before12.5 µg/m³ Event33.5 µg/m³ After28 µg/m³
Carbon monoxide 0.485 ppm
About the same as surrounding days
Before0.520 ppm Event0.485 ppm After0.375 ppm
Nitrogen dioxide 4.77 ppb
27% higher than surrounding days
Before3.08 ppb Event4.77 ppb After4.32 ppb
Sulfur dioxide 1.17 ppb
41% higher than surrounding days
Before1.09 ppb Event1.17 ppb After0.756 ppb
Ozone 0.007 ppm
39% lower than surrounding days
Before0.017 ppm Event0.007 ppm After0.012 ppm
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.
Air-mass reconstruction
Where the air had been
NOAA HYSPLIT traces the air arriving at each metro backward for 72 hours. Multiple arrival times and heights show whether the broad path is stable—or sensitive to assumptions about when and where the polluted layer arrived.
Air arriving near Urban Honolulu
Peak-date arrivals · 2009-05-04
Broad history Mostly east of the metro
72-hour reach 600–750 km
Sensitivity runs 12 modeled paths
Near surface · 100 mLower atmosphere · 500 mHigher layer · 1,000 m
Each line begins 72 hours before arrival and points toward the metro. Color represents arrival height; repeated lines represent 00, 06, 12, and 18 UTC arrival assumptions. A path can show where the air traveled, but it cannot prove which source added the PM2.5.
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 |
|---|---|---|---|---|
| Urban Honolulu, HI | 23.1 µg/m³ | 1.1 | May 4, 2009 | #24 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.
April-May 2009 Honolulu journal
Where the Heck Is Mom
A contemporaneous Honolulu account says vog from the Big Island was making the air look and feel poor during the exact period.
What it supports
A retained source supports the attributed cause for the stated place and dates.
Limit
This is a community observation, not an official air-quality determination or source-apportionment product.
What remains uncertain
- Vog is retained as a possible volcanic-emissions cause; the catalog vocabulary currently stores it under other.
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.