Dust EPA monitor flag
Daily PM2.5 peaked at 38.7 µg/m³ near San Antonio across 2 covered metros home to 5.3 million people.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 1.3 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 7.0 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 supplied retained evidence supports dust for this event; no supplied evidence establishes membership in a broader 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 31, 2024 official
EPA AQS carries an agency-submitted request-exclusion qualifier (RA, African Dust.) on 24 PM2.5 samples in the candidate CBSA on 2024-07-31, identifying windblown or transported dust as affecting the samples. A request-exclusion qualifier is an official submitting-agency causal claim, but this endpoint does not establish EPA concurrence.
U.S. EPA Air Quality System and the submitting air monitoring agency · Jul 31, 2024 official
EPA AQS carries an agency-submitted request-exclusion qualifier (RA, African Dust.) on 24 PM2.5 samples in the candidate CBSA on 2024-07-31, identifying windblown or transported dust as affecting the samples. A request-exclusion qualifier is an official submitting-agency causal claim, but this endpoint does not establish EPA concurrence.
Texas Commission on Environmental Quality · Aug 4, 2025 official
TCEQ identifies Saharan Desert dust as the July 31 exceptional-event source at Travis County monitors, supporting the Austin portion of this event; it does not assess San Antonio.
See every retained source and limitation ↓
Sequence: San Antonio (Jul 31) → Austin (Jul 31)
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 request-exclusion qualifier (RA, African Dust.) on 24 PM2.5 samples in the candidate CBSA on 2024-07-31, identifying windblown or transported dust as affecting the samples. A request-exclusion qualifier is an…
View supporting source ↗Air-mass movement
The retained record does not yet show how air traveled from the proposed source to these metros. A trajectory replay or dated plume analysis belongs here.
Local response
EPA monitors recorded the event across 2 metros. The peak daily concentration is roughly 1.8 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 2024-07-28 to 2024-08-03 · PM2.5 target: Austin Webberville Rd
269% above nearby days
26% higher than surrounding days
371% higher than surrounding days
269% higher than surrounding days
371% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
25% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
26% higher than surrounding days
San Antonio-New Braunfels, TX
Monitor comparison window 2024-07-28 to 2024-08-03 · PM2.5 target: San Antonio Bulverde Parkway
247% above nearby days
39% higher than surrounding days
323% higher than surrounding days
247% higher than surrounding days
323% higher than surrounding days
13% higher than surrounding days
About the same as surrounding days
8% lower than surrounding days
About the same as surrounding days
About the same as surrounding days
39% 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.
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 |
|---|---|---|---|---|
| San Antonio-New Braunfels, TX | 38.7 µg/m³ | 1.8 | Jul 31, 2024 | #18 of its top days |
| Austin-Round Rock, TX | 37.4 µg/m³ | 1.7 | Jul 31, 2024 | #15 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 RA — African Dust.
EPA AQS carries an agency-submitted request-exclusion qualifier (RA, African Dust.) on 24 PM2.5 samples in the candidate CBSA on 2024-07-31, identifying windblown or transported dust as affecting the samples. A request-exclusion qualifier is an official submitting-agency causal claim, but this endpoint does not establish EPA concurrence.
AQS PM2.5 qualifier RA — African Dust.
EPA AQS carries an agency-submitted request-exclusion qualifier (RA, African Dust.) on 24 PM2.5 samples in the candidate CBSA on 2024-07-31, identifying windblown or transported dust as affecting the samples. A request-exclusion qualifier is an official submitting-agency causal claim, but this endpoint does not establish EPA concurrence.
Exceptional event demonstration: PM2.5 summary for Harrison, Kleberg, and Travis Counties, 2022-2024
TCEQ identifies Saharan Desert dust as the July 31 exceptional-event source at Travis County monitors, supporting the Austin portion of this event; it does not assess San Antonio.
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.