Wildfire smoke EPA monitor flag
Daily PM2.5 peaked at 55.7 µg/m³ near McAllen across 4 covered metros home to 14 million people. 3 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 ≈ 2.4 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 33 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
TCEQ and contemporaneous reporting identify the same Mexico and Central America fire-smoke transport affecting South, Central, and Southeast Texas over May 8-10. The overlapping metro events are grouped as one regional occurrence.
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 · May 8, 2024 official
EPA AQS carries an agency-submitted request-exclusion qualifier (RG, Fire - Mexico/Central America.) on 24 PM2.5 samples in the candidate CBSA on 2024-05-08, identifying wildfire smoke 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 · May 9, 2024 official
EPA AQS carries an agency-submitted request-exclusion qualifier (RG, Fire - Mexico/Central America.) on 24 PM2.5 samples in the candidate CBSA on 2024-05-09, identifying wildfire smoke 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 · May 10, 2024 official
EPA AQS carries an agency-submitted request-exclusion qualifier (RG, Fire - Mexico/Central America.) on 24 PM2.5 samples in the candidate CBSA on 2024-05-10, identifying wildfire smoke as affecting the samples. A request-exclusion qualifier is an official submitting-agency causal claim, but this endpoint does not establish EPA concurrence.
See every retained source and limitation ↓
Sequence: McAllen (May 8) → Austin (May 8) → San Antonio (May 8) → Houston (May 9)
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 (RG, Fire - Mexico/Central America.) on 24 PM2.5 samples in the candidate CBSA on 2024-05-08, identifying wildfire smoke as affecting the samples. A request-exclusion qualifier is an…
View supporting source ↗Air-mass movement
Contemporaneous reporting, citing TCEQ conditions, linked the Central and South Texas haze and elevated PM2.5 to smoke from burnings in Mexico and Central America.
View transport source ↗Local response
EPA monitors recorded the event across 4 metros. The peak daily concentration is roughly 2.5 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.
McAllen-Edinburg-Mission, TX
Monitor comparison window 2024-05-05 to 2024-05-13 · PM2.5 target: Mission
21% above nearby days
9% lower than surrounding days
22% higher than surrounding days
21% higher than surrounding days
22% higher than surrounding days
34% higher than surrounding days
About the same as surrounding days
9% lower than surrounding days
Austin-Round Rock, TX
Monitor comparison window 2024-05-05 to 2024-05-12 · PM2.5 target: Austin Webberville Rd
178% above nearby days
About the same as surrounding days
111% higher than surrounding days
178% higher than surrounding days
111% higher than surrounding days
28% higher than surrounding days
22% higher than surrounding days
33% lower than surrounding days
9% higher than surrounding days
6% higher than surrounding days
About the same as surrounding days
San Antonio-New Braunfels, TX
Monitor comparison window 2024-05-05 to 2024-05-12 · PM2.5 target: San Antonio Bulverde Parkway
90% above nearby days
12% lower than surrounding days
59% higher than surrounding days
90% higher than surrounding days
59% higher than surrounding days
28% higher than surrounding days
About the same as surrounding days
149% higher than surrounding days
21% higher than surrounding days
5% higher than surrounding days
12% lower than surrounding days
Houston-The Woodlands-Sugar Land, TX
Monitor comparison window 2024-05-06 to 2024-05-12 · PM2.5 target: Houston North Wayside
213% above nearby days
22% lower than surrounding days
116% higher than surrounding days
213% higher than surrounding days
116% higher than surrounding days
56% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
22% 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.
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 |
|---|---|---|---|---|
| McAllen-Edinburg-Mission, TX | 55.7 µg/m³ | 6.6 | May 10, 2024 | #7 of its top days |
| Austin-Round Rock, TX | 51.8 µg/m³ | 4.0 | May 8, 2024 | #4 of its top days |
| San Antonio-New Braunfels, TX | 47.3 µg/m³ | 4.0 | May 8, 2024 | #8 of its top days |
| Houston-The Woodlands-Sugar Land, TX | 44.7 µg/m³ | 2.0 | May 9, 2024 | #14 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 RG — Fire - Mexico/Central America.
EPA AQS carries an agency-submitted request-exclusion qualifier (RG, Fire - Mexico/Central America.) on 24 PM2.5 samples in the candidate CBSA on 2024-05-08, identifying wildfire smoke 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 RG — Fire - Mexico/Central America.
EPA AQS carries an agency-submitted request-exclusion qualifier (RG, Fire - Mexico/Central America.) on 24 PM2.5 samples in the candidate CBSA on 2024-05-09, identifying wildfire smoke 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 RG — Fire - Mexico/Central America.
EPA AQS carries an agency-submitted request-exclusion qualifier (RG, Fire - Mexico/Central America.) on 24 PM2.5 samples in the candidate CBSA on 2024-05-10, identifying wildfire smoke 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 RG — Fire - Mexico/Central America.
EPA AQS carries an agency-submitted request-exclusion qualifier (RG, Fire - Mexico/Central America.) on 24 PM2.5 samples in the candidate CBSA on 2024-05-09, identifying wildfire smoke 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 RG — Fire - Mexico/Central America.
EPA AQS carries an agency-submitted request-exclusion qualifier (RG, Fire - Mexico/Central America.) on 23 PM2.5 samples in the candidate CBSA on 2024-05-09, identifying wildfire smoke 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 RG — Fire - Mexico/Central America.
EPA AQS carries an agency-submitted request-exclusion qualifier (RG, Fire - Mexico/Central America.) on 48 PM2.5 samples in the candidate CBSA on 2024-05-08, identifying wildfire smoke 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 RG — Fire - Mexico/Central America.
EPA AQS carries an agency-submitted request-exclusion qualifier (RG, Fire - Mexico/Central America.) on 24 PM2.5 samples in the candidate CBSA on 2024-05-08, identifying wildfire smoke as affecting the samples. A request-exclusion qualifier is an official submitting-agency causal claim, but this endpoint does not establish EPA concurrence.
Summary of 2024 Exceptional Event Demonstration for Fine Particulate Matter at Other Counties
TCEQ identifies May 8, 2024 PM2.5 exceptional events in Hidalgo and other South Texas counties as smoke from fires in Mexico/Central America.
Texas cities face air quality concerns due to haze
Contemporaneous reporting, citing TCEQ conditions, linked the Central and South Texas haze and elevated PM2.5 to smoke from burnings in Mexico and Central America.
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.