Wildfire smoke EPA monitor flag
Daily PM2.5 peaked at 36.1 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 ≈ 1.2 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 6.3 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
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 · Apr 1, 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 2024-04-01, 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 · Apr 1, 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 2024-04-01, 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: San Antonio (Apr 1) → Austin (Apr 1)
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 2024-04-01, identifying wildfire smoke as affecting the samples. A request-exclusion qualifier is an…
View supporting source ↗Air-mass movement
NOAA HYSPLIT modeled 24 backward paths across multiple arrival times and heights. They show where the air traveled, not which source polluted it.
Explore the modeled paths ↓Local response
EPA monitors recorded the event across 2 metros. The peak daily concentration is roughly 1.6 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.
Austin-Round Rock, TX
Monitor comparison window 2024-03-29 to 2024-04-04 · PM2.5 target: Austin Webberville Rd
254% above nearby days
20% higher than surrounding days
148% higher than surrounding days
254% higher than surrounding days
148% higher than surrounding days
11% higher than surrounding days
About the same as surrounding days
27% higher than surrounding days
15% lower than surrounding days
8% higher than surrounding days
20% higher than surrounding days
San Antonio-New Braunfels, TX
Monitor comparison window 2024-03-29 to 2024-04-04 · PM2.5 target: San Antonio Bulverde Parkway
321% above nearby days
13% higher than surrounding days
233% higher than surrounding days
321% higher than surrounding days
233% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
1034% higher than surrounding days
6% lower than surrounding days
10% higher than surrounding days
13% 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 · 2024-04-01
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 San Antonio-New Braunfels
Peak-date arrivals · 2024-04-01
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 |
|---|---|---|---|---|
| San Antonio-New Braunfels, TX | 36.1 µg/m³ | 1.6 | Apr 1, 2024 | #23 of its top days |
| Austin-Round Rock, TX | 34.2 µg/m³ | 1.6 | Apr 1, 2024 | #24 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 2024-04-01, 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 2024-04-01, 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.
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.