NASA Earth Observatory corroborates
Fires in Mexico and Central America
NASA imagery shows smoke from agricultural and other fires in Mexico and Central America spreading across the Gulf into the southern United States during the event.
Prescribed fire Likely
2003-05-08 to 2003-05-11 Dallas-Fort Worth-Arlington, TX, Houston-The Woodlands-Sugar Land, TX, and 1 other metros prescribed-fire smoke episode
Daily PM2.5 peaked at 56.7 µg/m³ near Dallas across 3 covered metros home to 17 million people. 2 metros 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 ≈ 3.3 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 56 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 basis for “Prescribed fire”
Manual research connected 3 source events to one prescribed-fire smoke episode using the deterministic grouping rule.
Likely Applicable reporting or a supported inference makes this the best current causal explanation.
NASA Earth Observatory · May 12, 2003 corroborates
Smoke from Yucatan Fires Reaches Gulf Coast States
NASA's May 11 satellite analysis shows smoke from intense Central American burning entrained over the Gulf Coast states.
Houston Chronicle via MyPlainview · May 11, 2003 corroborates
New alert issued for smoke from Mexico, Central America
Contemporaneous Texas reporting says the state's smoky haze peaked over the weekend and came from agricultural fires in Mexico and Central America.
See every retained source and limitation ↓
Sequence: Dallas (May 8) → McAllen (May 9) → Houston (May 11)
Evidence path
From source to city
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.
- 1Documented
Source or mechanism
Prescribed fire
NASA imagery shows smoke from agricultural and other fires in Mexico and Central America spreading across the Gulf into the southern United States during the event.
View supporting source ↗ - 2Documented
Air-mass movement
Transport into the affected region is documented
NASA imagery shows smoke from agricultural and other fires in Mexico and Central America spreading across the Gulf into the southern United States during the event.
View transport source ↗ - 3Documented
Local response
56.7 µg/m³ near Dallas
EPA monitors recorded the event across 3 metros. The peak daily concentration is roughly 2.6 cigarette-equivalents at the outdoor daily rate.
Inspect the pollutant and weather signals ↓
Event autopsy
What the instruments saw
Before, during, and after the episode: nearby pollutant monitors and surface-weather stations show what changed. This context tests the “Prescribed fire” explanation; it does not assign the cause by itself.
Dallas-Fort Worth-Arlington, TX
Monitor comparison window 2003-05-05 to 2003-05-13 · PM2.5 target: Fort Worth Northwest
52% above nearby days
62% higher than surrounding days
No adjacent-day comparison
Pollution fingerprint
Metro-wide median of reporting monitors PM2.5 41.9 µg/m³
52% higher than surrounding days
Before27.5 µg/m³ Event41.9 µg/m³ After6.80 µg/m³
PM10 64 µg/m³
No adjacent-day comparison
Before— Event64 µg/m³ After—
Carbon monoxide 0.592 ppm
21% higher than surrounding days
Before0.504 ppm Event0.592 ppm After0.362 ppm
Nitrogen dioxide 5.08 ppb
21% lower than surrounding days
Before6.46 ppb Event5.08 ppb After7.92 ppb
Sulfur dioxide 0.283 ppb
239% higher than surrounding days
Before0.083 ppb Event0.283 ppb After0.083 ppb
Ozone 0.045 ppm
About the same as surrounding days
Before0.038 ppm Event0.045 ppm After0.035 ppm
Atmospheric conditions
Nearby EPA weather observationsAbout the same as surrounding days
About the same as surrounding days
About the same as surrounding days
62% higher than surrounding days
McAllen-Edinburg-Mission, TX
Monitor comparison window 2003-05-06 to 2003-05-12 · PM2.5 target: Mission
0% above nearby days
18% higher than surrounding days
14% higher than surrounding days
Pollution fingerprint
Metro-wide median of reporting monitors PM2.5 52.6 µg/m³
About the same as surrounding days
Before52.9 µg/m³ Event52.6 µg/m³ After26.9 µg/m³
PM10 104 µg/m³
14% higher than surrounding days
Before91 µg/m³ Event104 µg/m³ After88 µg/m³
Ozone 0.043 ppm
About the same as surrounding days
Before0.043 ppm Event0.043 ppm After0.035 ppm
Atmospheric conditions
Nearby EPA weather observationsAbout the same as surrounding days
18% higher than surrounding days
Houston-The Woodlands-Sugar Land, TX
Monitor comparison window 2003-05-08 to 2003-05-14 · PM2.5 target: Clinton
49% above nearby days
42% lower than surrounding days
21% higher than surrounding days
Pollution fingerprint
Metro-wide median of reporting monitors PM2.5 33.2 µg/m³
49% higher than surrounding days
Before26.4 µg/m³ Event33.2 µg/m³ After16.4 µg/m³
Carbon monoxide 0.548 ppm
21% higher than surrounding days
Before0.458 ppm Event0.548 ppm After0.375 ppm
Nitrogen dioxide 5.41 ppb
About the same as surrounding days
Before4.92 ppb Event5.41 ppb After8.48 ppb
Sulfur dioxide 1.08 ppb
60% lower than surrounding days
Before3 ppb Event1.08 ppb After2.71 ppb
Ozone 0.032 ppm
38% higher than surrounding days
Before0.023 ppm Event0.032 ppm After0.018 ppm
Atmospheric conditions
Nearby EPA weather observationsAbout the same as surrounding days
About the same as surrounding days
About the same as surrounding days
42% 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.
Measured daily PM2.5 at EPA monitors, as cigarette-equivalents
EPA monitors sit in metro areas, so the colour clusters there. Land between and beyond
them is unmeasured, not clean: this map shows where IAQng has readings, not the extent
of the smoke.
—
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
Camera views near
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.
Affected metros
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| Dallas-Fort Worth-Arlington, TX | 56.7 µg/m³ | 6.7 | May 10, 2003 | #3 of its top days |
| McAllen-Edinburg-Mission, TX | 54 µg/m³ | 2.5 | May 9, 2003 | #9 of its top days |
| Houston-The Woodlands-Sugar Land, TX | 43.9 µg/m³ | 2.0 | May 11, 2003 | #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
What supports this account
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.
Smoke from Yucatan Fires Reaches Gulf Coast States
NASA Earth Observatory
NASA's May 11 satellite analysis shows smoke from intense Central American burning entrained over the Gulf Coast states.
What it supports
A retained source supports the attributed cause for the stated place and dates.
Limit
The satellite narrative is regional.
Fires in Mexico and Central America
NASA Earth Observatory
NASA imagery shows smoke from agricultural and other fires in Mexico and Central America spreading across the Gulf into the southern United States during the event.
What it supports
A retained source supports the attributed cause for the stated place and dates.
Fires in Mexico and Central America
NASA Earth Observatory
NASA reports smoke from scores of fires across southern Mexico and Central America spreading north over the Gulf and southern United States on the event date.
What it supports
A retained source supports the attributed cause for the stated place and dates.
New alert issued for smoke from Mexico, Central America
Houston Chronicle via MyPlainview
Contemporaneous Texas reporting says the state's smoky haze peaked over the weekend and came from agricultural fires in Mexico and Central America.
What it supports
A retained source supports the attributed cause for the stated place and dates.
Limit
The report does not identify individual fires.
What remains uncertain
- No individual fire is assigned as the source.
- The classification is bounded to the retained evidence and does not apportion every source contributing to the daily PM2.5 value.
Status and provenance
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.