Dust EPA monitor flag
Daily PM2.5 peaked at 49.7 µg/m³ near Dallas across 2 covered metros home to 11 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 ≈ 3.1 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 34 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 dust as the broad cause for this time-bounded episode.
EPA monitor flag EPA attached an exceptional-event qualifier to the affected samples. The agency flagged the measurement itself; no separate agency record describes the event.
U.S. EPA Air Quality System and the submitting air monitoring agency · Jul 1, 2018 official
EPA AQS carries an agency-submitted informational qualifier (IA, African Dust.) on 7 PM2.5 samples in the candidate CBSA on 2018-07-01, identifying windblown or transported dust as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
U.S. EPA Air Quality System and the submitting air monitoring agency · Jul 1, 2018 official
EPA AQS carries an agency-submitted informational qualifier (IA, African Dust.) on 2 PM2.5 samples in the candidate CBSA on 2018-07-01, identifying windblown or transported dust as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
The Dallas Morning News · Jul 1, 2018 corroborates
Contemporaneous reporting, citing the Texas Commission on Environmental Quality forecast, says Saharan dust was affecting Texas and could reach Dallas–Fort Worth and Austin.
See every retained source and limitation ↓
Sequence: Dallas (Jun 30) → Austin (Jun 30)
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
EPA AQS carries an agency-submitted informational qualifier (IA, African Dust.) on 7 PM2.5 samples in the candidate CBSA on 2018-07-01, identifying windblown or transported dust as affecting the samples. An informational qualifier is an official…
View supporting source ↗Air-mass movement
Contemporaneous reporting, citing the Texas Commission on Environmental Quality forecast, says Saharan dust was affecting Texas and could reach Dallas–Fort Worth and Austin.
View transport source ↗Local response
EPA monitors recorded the event across 2 metros. The peak daily concentration is roughly 2.3 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.
Austin-Round Rock, TX
Monitor comparison window 2018-06-27 to 2018-07-04 · PM2.5 target: Austin North Interstate 35
69% above nearby days
17% higher than surrounding days
No adjacent-day comparison
69% higher than surrounding days
No adjacent-day comparison
About the same as surrounding days
27% lower than surrounding days
About the same as surrounding days
7% lower than surrounding days
About the same as surrounding days
17% higher than surrounding days
Dallas-Fort Worth-Arlington, TX
Monitor comparison window 2018-06-27 to 2018-07-04 · PM2.5 target: Dallas Hinton
98% above nearby days
15% higher than surrounding days
No adjacent-day comparison
98% higher than surrounding days
No adjacent-day comparison
About the same as surrounding days
33% lower than surrounding days
About the same as surrounding days
13% lower than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
15% 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
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 Austin-Round Rock
Peak-date arrivals · 2018-07-01
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.
Air arriving near Dallas-Fort Worth-Arlington
Peak-date arrivals · 2018-07-01
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.
Views from the selected metro
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.
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| Dallas-Fort Worth-Arlington, TX | 49.7 µg/m³ | 4.3 | Jul 1, 2018 | #8 of its top days |
| Austin-Round Rock, TX | 36.6 µg/m³ | 3.3 | Jul 1, 2018 | #16 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.
AQS PM2.5 qualifier IA — African Dust.
EPA AQS carries an agency-submitted informational qualifier (IA, African Dust.) on 7 PM2.5 samples in the candidate CBSA on 2018-07-01, identifying windblown or transported dust as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
AQS PM2.5 qualifier IA — African Dust.
EPA AQS carries an agency-submitted informational qualifier (IA, African Dust.) on 2 PM2.5 samples in the candidate CBSA on 2018-07-01, identifying windblown or transported dust as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
Dust from Africa brought hazy skies to Dallas-Fort Worth this weekend
Contemporaneous reporting, citing the Texas Commission on Environmental Quality forecast, says Saharan dust was affecting Texas and could reach Dallas–Fort Worth and Austin.
EPA monitor flag EPA attached an exceptional-event qualifier to the affected samples. The agency flagged the measurement itself; no separate agency record describes the event.
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.