Wildfire smoke EPA monitor flag
Daily PM2.5 peaked at 51.4 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 ≈ 1.9 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 1.8 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 supplied evidence supports wildfire smoke as the root cause of this event. The supplied record does not establish a coherent shared occurrence with neighboring candidates, so the episode remains event-specific.
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 16, 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 2024-05-16, 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.
Texas Commission on Environmental Quality · Aug 4, 2025 official
TCEQ's May 16 assessment documents smoke from Mexico/Central America transported along the Texas coast, supported by trajectories and satellite imagery; it is regional evidence adjacent to, rather than a monitor-level attribution for, McAllen.
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 2024-05-16, identifying wildfire smoke as affecting the samples. A request-exclusion qualifier is an…
View supporting source ↗Air-mass movement
TCEQ's May 16 assessment documents smoke from Mexico/Central America transported along the Texas coast, supported by trajectories and satellite imagery; it is regional evidence adjacent to, rather than a monitor-level attribution for, McAllen.
View transport source ↗Local response
EPA monitors recorded the event across 1 metro. 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 “Wildfire smoke” explanation; it does not assign the cause by itself.
McAllen-Edinburg-Mission, TX
Monitor comparison window 2024-05-13 to 2024-05-19 · PM2.5 target: Mission
47% above nearby days
20% higher than surrounding days
38% higher than surrounding days
47% higher than surrounding days
38% higher than surrounding days
14% lower than surrounding days
About the same as surrounding days
20% 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.
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| McAllen-Edinburg-Mission, TX | 51.4 µg/m³ | 2.3 | May 16, 2024 | #11 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 2024-05-16, 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.
TCEQ's May 16 assessment documents smoke from Mexico/Central America transported along the Texas coast, supported by trajectories and satellite imagery; it is regional evidence adjacent to, rather than a monitor-level attribution for, McAllen.
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.