Dust Likely
Daily PM2.5 peaked at 42.8 µg/m³ near Miami across 1 covered metro home to 6.5 million people.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 1.5 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 10 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
Contemporaneous reporting places Saharan dust in South Florida on the exact event date and explicitly connects it with degraded southeastern Florida air quality.
Likely Applicable reporting or a supported inference makes this the best current causal explanation.
AccuWeather · Jun 16, 2021 corroborates
Reporting updated June 18, citing NWS Miami, said Saharan dust was reaching South Florida Friday or Saturday and noted poor air quality already affecting southeastern Florida.
Chicago Sun-Times / Associated Press · Jun 16, 2021 hypothesis
The opened report forecasts a major Saharan dust outbreak across Florida in the candidate period and says it may worsen air pollution, citing a University of Miami dust expert and an NWS Miami meteorologist. It supports a transport hypothesis, not confirmed surface attribution for Miami on June 18.
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
Reporting updated June 18, citing NWS Miami, said Saharan dust was reaching South Florida Friday or Saturday and noted poor air quality already affecting southeastern Florida.
View supporting source ↗Air-mass movement
The opened report forecasts a major Saharan dust outbreak across Florida in the candidate period and says it may worsen air pollution, citing a University of Miami dust expert and an NWS Miami meteorologist. It supports a transport hypothesis, not…
View transport source ↗Local response
EPA monitors recorded the event across 1 metro. The peak daily concentration is roughly 1.9 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.
Miami-Fort Lauderdale-West Palm Beach, FL
Monitor comparison window 2021-06-15 to 2021-06-21 · PM2.5 target: HOMESTEAD FIRE STATION
61% above nearby days
35% higher than surrounding days
72% higher than surrounding days
61% higher than surrounding days
72% higher than surrounding days
20% lower than surrounding days
35% lower than surrounding days
30% lower than surrounding days
22% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
35% 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 |
|---|---|---|---|---|
| Miami-Fort Lauderdale-West Palm Beach, FL | 42.8 µg/m³ | 1.9 | Jun 18, 2021 | #18 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.
AccuWeather
Reporting updated June 18, citing NWS Miami, said Saharan dust was reaching South Florida Friday or Saturday and noted poor air quality already affecting southeastern Florida.
A retained source supports the attributed cause for the stated place and dates.
The report does not quantify the dust contribution at the specific regulatory 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.