Wildfire smoke Agency determination
Named source Palm Beach County brush fire
Daily PM2.5 peaked at 46.9 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 ≈ 1.7 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 11 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
Qualified frozen evidence supports wildfire smoke as the broad root cause.
Agency determination A government body issued a record naming this cause for this event: an NWS air-quality alert, a NOAA Storm Events record, or a state or local official archive.
NOAA/NCEI Storm Events Database corroborates
NOAA records a lightning-initiated Palm Beach County brush fire through May 25 and states that its smoke drifted across Palm Beach, Broward, and Dade metropolitan areas, prompting health alerts. This corroborates wildfire smoke in the event place and window but does not quantify its contribution to measured surface PM2.5.
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
NOAA states that smoke from the Palm Beach County brush fire drifted across the Palm Beach, Broward, and Dade metropolitan areas during the episode.
View supporting source ↗Air-mass movement
NOAA records a lightning-initiated Palm Beach County brush fire through May 25 and states that its smoke drifted across Palm Beach, Broward, and Dade metropolitan areas, prompting health alerts. This corroborates wildfire smoke in the event place…
View transport source ↗Local response
EPA monitors recorded the event across 1 metro. The peak daily concentration is roughly 2.1 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 “Wildfire smoke” explanation; it does not assign the cause by itself.
Miami-Fort Lauderdale-West Palm Beach, FL
Monitor comparison window 1999-05-22 to 1999-05-28
76% above nearby days
6% lower than surrounding days
11% higher than surrounding days
76% higher than surrounding days
11% higher than surrounding days
31% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
7% lower than surrounding days
About the same as surrounding days
6% lower 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.
Air-mass reconstruction
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 Miami-Fort Lauderdale-West Palm Beach
Peak-date arrivals · 1999-05-25
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.
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 | 46.9 µg/m³ | 2.1 | May 25, 1999 | #12 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.
May 1999 South Florida wildfire and smoke episode
NOAA records a lightning-initiated Palm Beach County brush fire through May 25 and states that its smoke drifted across Palm Beach, Broward, and Dade metropolitan areas, prompting health alerts. This corroborates wildfire smoke in the event place and window but does not quantify its contribution to measured surface PM2.5.
Agency determination A government body issued a record naming this cause for this event: an NWS air-quality alert, a NOAA Storm Events record, or a state or local official archive.
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.