Prescribed fire Likely provisional
Daily PM2.5 peaked at 44.1 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 ≈ 1.6 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 1.5 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
NOAA observed a Mexico/Central America smoke-aerosol layer reaching the Gulf Coast on May 6; local residents simultaneously reported smoke in McAllen and pointed to cross-border burning, following local news attribution of the ongoing Valley haze to agricultural burns.
Likely Applicable reporting or a supported inference makes this the best current causal explanation.
NOAA Satellite Services Division · May 6, 2026 corroborates
NOAA's May 6 satellite narrative observed a light-to-moderate smoke/aerosol layer from southern Mexico and Central America extending across the Gulf Coast, with the northern edge partly obscured by clouds.
r/RioGrandeValley · May 6, 2026 hypothesis
Rio Grande Valley residents reported visible and odorous smoke on May 6 and repeatedly identified agricultural or refuse burning south of the border as the suspected source.
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
NOAA's May 6 satellite narrative observed a light-to-moderate smoke/aerosol layer from southern Mexico and Central America extending across the Gulf Coast, with the northern edge partly obscured by clouds.
View supporting source ↗Air-mass movement
NOAA's May 6 satellite narrative observed a light-to-moderate smoke/aerosol layer from southern Mexico and Central America extending across the Gulf Coast, with the northern edge partly obscured by clouds.
View transport source ↗Local response
EPA monitors recorded the event across 1 metro. The peak daily concentration is roughly 2.0 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.
McAllen-Edinburg-Mission, TX
Monitor comparison window 2026-05-03 to 2026-05-09
The PM2.5 event remains in the catalog, but the surrounding monitoring record cannot supply a defensible instrument fingerprint for this place and date.
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 | 44.1 µg/m³ | 2.0 | May 6, 2026 | #16 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.
NOAA Satellite Services Division
NOAA's May 6 satellite narrative observed a light-to-moderate smoke/aerosol layer from southern Mexico and Central America extending across the Gulf Coast, with the northern edge partly obscured by clouds.
A retained source supports the attributed cause for the stated place and dates.
The satellite narrative does not by itself prove how much of the layer mixed to the surface at McAllen.
r/RioGrandeValley
Rio Grande Valley residents reported visible and odorous smoke on May 6 and repeatedly identified agricultural or refuse burning south of the border as the suspected source.
This source supports a possible mechanism or occurrence; it does not establish the cause by itself.
Community observations are not an official causal determination and comments disagreed about whether agricultural fields or refuse were burning.
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. Recent days are preliminary AirNow readings and re-rank once EPA certifies them. 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.