Dust Documented
Daily PM2.5 peaked at 47.4 µg/m³ near Houston across 1 covered metro home to 7.8 million people. 1 metro 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 ≈ 1.6 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 12 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
Supplied qualified evidence supports dust as the root cause. The grouping includes only events linked by explicit shared episode evidence; otherwise this remains a single-event episode.
Documented An agency or publisher page assesses this cause, without an agency record naming the event or an EPA qualifier on the data.
Texas Commission on Environmental Quality official
TCEQ's exceptional-event analysis documents transported windblown dust entering Harris County on January 16 and includes Houston Deer Park PM2.5 soil measurements, supporting continuity into the locally reported January 17 haze.
KPRC 2 Click2Houston · Jan 17, 2021 corroborates
Contemporaneous Houston reporting identified a Texas windblown-dust plume over the city on January 17 and said small local fires may also have contributed to the haze.
lmtonline.com · Jan 22, 2021 corroborates
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
Contemporaneous Houston reporting identified a Texas windblown-dust plume over the city on January 17 and said small local fires may also have contributed to the haze.
View supporting source ↗Air-mass movement
TCEQ's exceptional-event analysis documents transported windblown dust entering Harris County on January 16 and includes Houston Deer Park PM2.5 soil measurements, supporting continuity into the locally reported January 17 haze.
View transport source ↗Local response
EPA monitors recorded the event across 1 metro. The peak daily concentration is roughly 2.2 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 “Dust” explanation; it does not assign the cause by itself.
Houston-The Woodlands-Sugar Land, TX
Monitor comparison window 2021-01-14 to 2021-01-20 · PM2.5 target: Houston East
92% above nearby days
45% lower than surrounding days
265% higher than surrounding days
92% higher than surrounding days
265% higher than surrounding days
48% higher than surrounding days
205% higher than surrounding days
16% lower than surrounding days
30% lower than surrounding days
About the same as surrounding days
About the same as surrounding days
45% 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 |
|---|---|---|---|---|
| Houston-The Woodlands-Sugar Land, TX | 47.4 µg/m³ | 2.2 | Jan 17, 2021 | #9 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.
TCEQ's exceptional-event analysis documents transported windblown dust entering Harris County on January 16 and includes Houston Deer Park PM2.5 soil measurements, supporting continuity into the locally reported January 17 haze.
Car covered in dust this weekend? Here's why
Contemporaneous Houston reporting identified a Texas windblown-dust plume over the city on January 17 and said small local fires may also have contributed to the haze.
Documented An agency or publisher page assesses this cause, without an agency record naming the event or an EPA qualifier on the data.
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.