Dust Likely
Daily PM2.5 peaked at 30.3 µg/m³ near Tucson across 1 covered metro home to 1.1 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 ≈ 1.1 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 1.2 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 National Weather Service explicitly attributed Tucson's March 28 haze to suspended dust from strong gusty winds, and same-day community reports independently described widespread dust, reduced visibility, odor, and respiratory irritation.
Likely Applicable reporting or a supported inference makes this the best current causal explanation.
National Weather Service Tucson · Mar 28, 2026 official
NWS Tucson said strong gusty east winds suspended dust across southeast Arizona and produced hazy skies on March 28, with visibility reduced to roughly five to seven miles.
r/Tucson · Mar 28, 2026 hypothesis
Same-day Tucson residents reported extreme wind, visible dust and haze, reduced sky visibility, dust odor, and eye or respiratory irritation; users also shared the contemporaneous NWS discussion.
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 Tucson said strong gusty east winds suspended dust across southeast Arizona and produced hazy skies on March 28, with visibility reduced to roughly five to seven miles.
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 “Dust” explanation; it does not assign the cause by itself.
Tucson, AZ
Monitor comparison window 2026-03-25 to 2026-03-31 · PM2.5 target: COACHLINE
285% above nearby days
42% higher than surrounding days
511% higher than surrounding days
285% higher than surrounding days
511% higher than surrounding days
About the same as surrounding days
40% lower than surrounding days
14% 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
42% 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 |
|---|---|---|---|---|
| Tucson, AZ | 30.3 µg/m³ | 1.4 | Mar 28, 2026 | #8 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 Tucson
NWS Tucson said strong gusty east winds suspended dust across southeast Arizona and produced hazy skies on March 28, with visibility reduced to roughly five to seven miles.
An official source supports the attributed cause for the stated place and dates.
The forecast discussion explains the observed haze but does not apportion the daily PM2.5 mass.
r/Tucson
Same-day Tucson residents reported extreme wind, visible dust and haze, reduced sky visibility, dust odor, and eye or respiratory irritation; users also shared the contemporaneous NWS discussion.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
Community observations corroborate conditions but are not a quantitative attribution method.
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.