volcanic_emissions Possible
Daily PM2.5 peaked at 29.9 µg/m³ near Urban Honolulu across 1 covered metro home to 998,747 people.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 1.1 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 1.1 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 exact-date NWS discussion explicitly placed vog from Big Island volcanic sources across the smaller islands, including Oahu in its transport discussion. A separate University of Hawaii study identifies January 2010 as a frequent-vog period on Oahu. The official statement supports volcanic emissions as possible, while the lack of monitor-level apportionment prevents a stronger label.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
National Weather Service Honolulu via Iowa Environmental Mesonet · Jan 23, 2010 official
On January 23, NWS Honolulu said vog from Big Island volcanic sources would continue across the smaller islands that night and specifically discussed the possibility of it clearing near Oahu only after the approaching front shifted winds.
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
On January 23, NWS Honolulu said vog from Big Island volcanic sources would continue across the smaller islands that night and specifically discussed the possibility of it clearing near Oahu only after the approaching front shifted winds.
View supporting source ↗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 1.4 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 “volcanic_emissions” explanation; it does not assign the cause by itself.
Urban Honolulu, HI
Monitor comparison window 2010-01-20 to 2010-01-26 · PM2.5 target: Sand Island
110% above nearby days
4 calm hours observed
Haze reported during 8 hours
110% higher than surrounding days
38% higher than surrounding days
7% lower than surrounding days
100% lower than surrounding days
108% higher than surrounding days
7% lower than surrounding days
12 kt maximum · 4 of 24 observed hours calm
0 observed hours at or below 3 miles
68°F to 81°F
81% maximum
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 |
|---|---|---|---|---|
| Urban Honolulu, HI | 29.9 µg/m³ | 1.4 | Jan 23, 2010 | #17 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.
National Weather Service Honolulu via Iowa Environmental Mesonet
On January 23, NWS Honolulu said vog from Big Island volcanic sources would continue across the smaller islands that night and specifically discussed the possibility of it clearing near Oahu only after the approaching front shifted winds.
An official source supports the attributed cause for the stated place and dates.
The NWS discussion describes the island-scale vog air mass and does not attribute a measured fraction of Honolulu's daily PM2.5 value.
University of Hawaii
The study reports frequent vog on Oahu during January 2010 but does not identify January 23 as a specific event.
Context for the event; this item does not establish the attributed cause by itself.
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.