NASA Earth Observatory · Jun 29, 2018 corroborates
Here Comes the Saharan Dust
NASA tracked a major Saharan dust plume across the Atlantic and forecast its arrival in Texas over the June 30 weekend.
Dust Likely
2018-06-30 McAllen-Edinburg-Mission, TX dust episode
Daily PM2.5 peaked at 41.3 µg/m³ near McAllen across 1 covered metro home to 914,820 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 ≈ 1.3 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 “Dust”
NASA and contemporaneous Texas reporting place a Saharan dust plume over Texas during the exact weekend.
Likely Applicable reporting or a supported inference makes this the best current causal explanation.
FOX 26 Houston · Jun 29, 2018 corroborates
Heat, Saharan dust during the weekend
Contemporaneous Texas weather reporting warned that Saharan dust would affect the state during the event weekend.
The Dallas Morning News · Jul 1, 2018 corroborates
Dust from Africa brought hazy skies to Dallas-Fort Worth this weekend
Contemporaneous reporting, citing the Texas Commission on Environmental Quality, identifies Saharan dust affecting the Texas coast, including the Brownsville–McAllen area.
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
Dust
NASA tracked a major Saharan dust plume across the Atlantic and forecast its arrival in Texas over the June 30 weekend.
View supporting source ↗ - 2Documented
Air-mass movement
Transport into the affected region is documented
Contemporaneous reporting, citing the Texas Commission on Environmental Quality, identifies Saharan dust affecting the Texas coast, including the Brownsville–McAllen area.
View transport source ↗ - 3Documented
Local response
41.3 µg/m³ near McAllen
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
What the instruments saw
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.
McAllen-Edinburg-Mission, TX
Monitor comparison window 2018-06-27 to 2018-07-03 · PM2.5 target: Mission
46% above nearby days
26% higher than surrounding days
Pollution fingerprint
Metro-wide median of reporting monitors PM2.5 41.4 µg/m³
46% higher than surrounding days
Before15.8 µg/m³ Event41.4 µg/m³ After28.3 µg/m³
Ozone 0.017 ppm
About the same as surrounding days
Before0.017 ppm Event0.017 ppm After0.016 ppm
Atmospheric conditions
Nearby EPA weather observationsAbout the same as surrounding days
26% 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.
Air-mass reconstruction
Where the air had been
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 McAllen-Edinburg-Mission
Peak-date arrivals · 2018-06-30
Broad history Mostly southeast of the metro
72-hour reach 1,500–2,600 km
Sensitivity runs 12 modeled paths
Near surface · 100 mLower atmosphere · 500 mHigher layer · 1,000 m
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.
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.
Affected metros
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| McAllen-Edinburg-Mission, TX | 41.3 µg/m³ | 1.9 | Jun 30, 2018 | #21 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.
Here Comes the Saharan Dust
NASA Earth Observatory
NASA tracked a major Saharan dust plume across the Atlantic and forecast its arrival in Texas over the June 30 weekend.
What it supports
A retained source supports the attributed cause for the stated place and dates.
Limit
Satellite transport establishes regional dust presence, not the precise surface contribution at McAllen.
Heat, Saharan dust during the weekend
FOX 26 Houston
Contemporaneous Texas weather reporting warned that Saharan dust would affect the state during the event weekend.
What it supports
A retained source supports the attributed cause for the stated place and dates.
Limit
The report is statewide rather than monitor-specific.
What remains uncertain
- The sources do not quantify the dust share of daily PM2.5 in McAllen.
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.