Dust Likely
Daily PM2.5 peaked at 108.4 µg/m³ near Bakersfield across 1 covered metro home to 922,529 people.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 4.3 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 4.0 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
An exact-date NWS discussion explicitly links gusty conditions to blowing dust and an Air District health caution covering Bakersfield's Kern County valley area. The notice does not isolate the monitor-day PM2.5 fraction, so the estimate is likely rather than officially verified.
Likely Applicable reporting or a supported inference makes this the best current causal explanation.
National Weather Service San Joaquin Valley/Hanford via Iowa Environmental Mesonet · May 23, 2012 official
NWS Hanford reported gusts to 40 mph across the central and southern San Joaquin Valley, said they would create blowing dust, and stated that the Valley Air District had issued a health caution for the Valley portion of Kern County because of the dust.
KCRA 3 · May 23, 2012 hypothesis
A contemporaneous air-district warning said blowing dust could produce unhealthy particulate concentrations in the San Joaquin Valley. It does not determine the cause of the reported Bakersfield PM2.5 event.
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
NWS Hanford reported gusts to 40 mph across the central and southern San Joaquin Valley, said they would create blowing dust, and stated that the Valley Air District had issued a health caution for the Valley portion of Kern County because of the…
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
A contemporaneous air-district warning said blowing dust could produce unhealthy particulate concentrations in the San Joaquin Valley. It does not determine the cause of the reported Bakersfield PM2.5 event.
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 “Dust” explanation; it does not assign the cause by itself.
Bakersfield, CA
Monitor comparison window 2012-05-20 to 2012-05-26 · PM2.5 target: Mojave
9% below nearby days
17% higher than surrounding days
60% higher than surrounding days
9% lower than surrounding days
60% higher than surrounding days
16% lower than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
17% higher 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.
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| Bakersfield, CA | 108.4 µg/m³ | 4.9 | May 23, 2012 | #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.
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 San Joaquin Valley/Hanford via Iowa Environmental Mesonet
NWS Hanford reported gusts to 40 mph across the central and southern San Joaquin Valley, said they would create blowing dust, and stated that the Valley Air District had issued a health caution for the Valley portion of Kern County because of the dust.
An official source supports the attributed cause for the stated place and dates.
The official discussion covers the Valley portion of Kern County rather than naming the Bakersfield PM2.5 monitor.
Likely Applicable reporting or a supported inference makes this the best current causal explanation.
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.