Prescribed fire Likely
Daily PM2.5 peaked at 35.2 µg/m³ near San Antonio across 1 covered metro home to 2.8 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 ≈ 3.3 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
NWS retrospectively identifies February 2026 as an early occurrence of Mexican vegetation-burning smoke transported as far north as San Antonio under southerly flow and an inversion. The exact San Antonio pollution fingerprint independently shows a sharp, broad particle and combustion-tracer response.
Likely Applicable reporting or a supported inference makes this the best current causal explanation.
National Weather Service Brownsville/Rio Grande Valley · Mar 1, 2026 official
NWS explains that vegetation-burning smoke carried north from Mexico can reach Austin and San Antonio under persistent southerly flow and inversions, and explicitly notes that this poor-air episode arrived as early as February in 2026.
MySA / NWS Brownsville · Feb 19, 2026 corroborates
Reporting based on NWS Brownsville attributed South Texas haze on February 19 to smoke and soot from Mexico trapped under a sharp inversion; San Antonio also registered elevated PM2.5 that day.
U.S. EPA Air Quality System; IAQng event-autopsy calculation v1 hypothesis
EPA observations show San Antonio PM2.5 near 33.3 µg/m³, about six times the preceding comparison value, while PM10 reached 57 µg/m³ and sulfur dioxide rose by roughly an order of magnitude. The broad particle and combustion-tracer response fits the NWS transported-smoke account.
Inference, not direct attribution
official_retrospective_transport_plus_exact_fingerprint_likely.v1: This inference is recorded in the catalog methodology.
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
NWS explains that vegetation-burning smoke carried north from Mexico can reach Austin and San Antonio under persistent southerly flow and inversions, and explicitly notes that this poor-air episode arrived as early as February in 2026.
View supporting source ↗Air-mass movement
NOAA HYSPLIT modeled 12 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 1 metro. 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 “Prescribed fire” explanation; it does not assign the cause by itself.
San Antonio-New Braunfels, TX
Monitor comparison window 2026-02-16 to 2026-02-22 · PM2.5 target: Von Ormy Highway 16
226% above nearby days
6% lower than surrounding days
73% higher than surrounding days
226% higher than surrounding days
73% higher than surrounding days
9% higher than surrounding days
6% lower than surrounding days
456% higher than surrounding days
9% lower than surrounding days
6% higher than surrounding days
6% 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.
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 San Antonio-New Braunfels
Peak-date arrivals · 2026-02-19
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 | 35.2 µg/m³ | 1.6 | Feb 19, 2026 | #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.
National Weather Service Brownsville/Rio Grande Valley
NWS explains that vegetation-burning smoke carried north from Mexico can reach Austin and San Antonio under persistent southerly flow and inversions, and explicitly notes that this poor-air episode arrived as early as February in 2026.
An official source supports the attributed cause for the stated place and dates.
The guide identifies the transported-smoke mechanism and geographic reach but does not quantify the San Antonio PM2.5 source fraction or name individual burns.
U.S. EPA Air Quality System; IAQng event-autopsy calculation v1
EPA observations show San Antonio PM2.5 near 33.3 µg/m³, about six times the preceding comparison value, while PM10 reached 57 µg/m³ and sulfur dioxide rose by roughly an order of magnitude. The broad particle and combustion-tracer response fits the NWS transported-smoke account.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
The descriptive metro fingerprint is not a collocated chemical source-apportionment result.
MySA / NWS Brownsville
Reporting based on NWS Brownsville attributed South Texas haze on February 19 to smoke and soot from Mexico trapped under a sharp inversion; San Antonio also registered elevated PM2.5 that day.
A retained source supports the attributed cause for the stated place and dates.
The NWS causal statement directly covers the Rio Grande Valley, not San Antonio.
Likely Applicable reporting or a supported inference makes this the best current causal explanation.
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.