Dust Agency determination
Daily PM2.5 peaked at 64.9 µg/m³ near San Antonio across 13 covered metros home to 31 million people. 2 metros recorded their worst day on record; 9 placed a top-ten day.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 2.0 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 62 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. Supplied qualified evidence supports dust as the root ca
Agency determination A government body issued a record naming this cause for this event: an NWS air-quality alert, a NOAA Storm Events record, or a state or local official archive.
U.S. EPA Air Quality System and the submitting air monitoring agency · Jun 26, 2020 official
EPA AQS carries an agency-submitted informational qualifier (IA, African Dust.) on 1 PM2.5 sample in the candidate CBSA on 2020-06-26, identifying windblown or transported dust as affecting the sample. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
U.S. EPA Air Quality System and the submitting air monitoring agency · Jun 26, 2020 official
EPA AQS carries an agency-submitted informational qualifier (IA, African Dust.) on 96 PM2.5 samples in the candidate CBSA on 2020-06-26, identifying windblown or transported dust as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
U.S. EPA Air Quality System and the submitting air monitoring agency · Jun 27, 2020 official
EPA AQS carries an agency-submitted informational qualifier (IA, African Dust.) on 1 PM2.5 sample in the candidate CBSA on 2020-06-27, identifying windblown or transported dust as affecting the sample. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
See every retained source and limitation ↓
Sequence: McAllen (Jun 26) → Houston (Jun 26) → Jackson (Jun 26) → San Antonio (Jun 27) → Austin (Jun 27) → Dallas (Jun 27) → Little Rock (Jun 27) → Tulsa (Jun 27) → Nashville (Jun 27) → Oklahoma City (Jun 27) → +3 more metros
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 informational qualifier (IA, African Dust.) on 1 PM2.5 sample in the candidate CBSA on 2020-06-26, identifying windblown or transported dust as affecting the sample. An informational qualifier is an official…
View supporting source ↗Air-mass movement
NASA documented the June 2020 Saharan plume reaching the United States and reported unhealthy fine-particle AQI levels in Texas on June 27. This supports regional dust transport, not unique apportionment of the McAllen monitor value.
View transport source ↗Local response
EPA monitors recorded the event across 13 metros. The peak daily concentration is roughly 3.0 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 “Dust” explanation; it does not assign the cause by itself.
San Antonio-New Braunfels, TX
Monitor comparison window 2020-06-24 to 2020-06-30 · PM2.5 target: Old Hwy 90
214% above nearby days
About the same as surrounding days
About the same as surrounding days
214% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
8% lower than surrounding days
About the same as surrounding days
About the same as surrounding days
McAllen-Edinburg-Mission, TX
Monitor comparison window 2020-06-23 to 2020-06-30 · PM2.5 target: Mission
154% above nearby days
About the same as surrounding days
No adjacent-day comparison
154% higher than surrounding days
No adjacent-day comparison
13% lower than surrounding days
About the same as surrounding days
About the same as surrounding days
Houston-The Woodlands-Sugar Land, TX
Monitor comparison window 2020-06-23 to 2020-06-30 · PM2.5 target: Galveston 99th Street
115% above nearby days
About the same as surrounding days
40% higher than surrounding days
115% higher than surrounding days
40% higher than surrounding days
6% higher than surrounding days
About the same as surrounding days
162% lower than surrounding days
15% lower than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
Austin-Round Rock, TX
Monitor comparison window 2020-06-23 to 2020-06-30 · PM2.5 target: Austin Webberville Rd
157% above nearby days
About the same as surrounding days
No adjacent-day comparison
157% higher than surrounding days
No adjacent-day comparison
9% higher than surrounding days
19% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
Dallas-Fort Worth-Arlington, TX
Monitor comparison window 2020-06-24 to 2020-06-30 · PM2.5 target: Haws Athletic Center
139% above nearby days
About the same as surrounding days
About the same as surrounding days
139% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
45% lower than surrounding days
9% lower than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
Little Rock-North Little Rock-Conway, AR
Monitor comparison window 2020-06-24 to 2020-06-30 · PM2.5 target: PARR
172% above nearby days
About the same as surrounding days
About the same as surrounding days
172% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
11% lower than surrounding days
5% lower than surrounding days
About the same as surrounding days
About the same as surrounding days
Oklahoma City, OK
Monitor comparison window 2020-06-24 to 2020-07-01 · PM2.5 target: MOORE
86% above nearby days
15% higher than surrounding days
112% higher than surrounding days
86% higher than surrounding days
112% higher than surrounding days
5% higher than surrounding days
41% lower than surrounding days
Adjacent observations available
27% lower than surrounding days
About the same as surrounding days
About the same as surrounding days
15% higher than surrounding days
Tulsa, OK
Monitor comparison window 2020-06-24 to 2020-07-01 · PM2.5 target: TULSA CENTRAL
112% above nearby days
29% higher than surrounding days
138% higher than surrounding days
112% higher than surrounding days
138% higher than surrounding days
17% lower than surrounding days
17% lower than surrounding days
35% lower than surrounding days
15% lower than surrounding days
About the same as surrounding days
About the same as surrounding days
29% higher than surrounding days
Wichita, KS
Monitor comparison window 2020-06-24 to 2020-07-01 · PM2.5 target: PECK
85% above nearby days
84% higher than surrounding days
85% higher than surrounding days
84% higher than surrounding days
16% lower than surrounding days
About the same as surrounding days
17% lower than surrounding days
Nashville-Davidson--Murfreesboro--Franklin, TN
Monitor comparison window 2020-06-24 to 2020-06-30 · PM2.5 target: Hendersonville
563% above nearby days
15% lower than surrounding days
563% higher than surrounding days
15% lower than surrounding days
48% lower than surrounding days
Adjacent observations available
26% lower than surrounding days
Jackson, MS
Monitor comparison window 2020-06-23 to 2020-06-29 · PM2.5 target: Jackson NCORE
233% above nearby days
30% lower than surrounding days
350% higher than surrounding days
233% higher than surrounding days
350% higher than surrounding days
326% higher than surrounding days
About the same as surrounding days
16% lower than surrounding days
12% higher than surrounding days
About the same as surrounding days
30% lower than surrounding days
Charleston-North Charleston, SC
Monitor comparison window 2020-06-24 to 2020-06-30 · PM2.5 target: CHARLESTON PUBLIC WORKS
321% above nearby days
43% higher than surrounding days
300% higher than surrounding days
321% higher than surrounding days
300% higher than surrounding days
27% lower than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
43% higher than surrounding days
Columbia, SC
Monitor comparison window 2020-06-24 to 2020-06-30 · PM2.5 target: PARKLANE
292% above nearby days
48% higher than surrounding days
378% higher than surrounding days
292% higher than surrounding days
378% higher than surrounding days
57% lower than surrounding days
35% lower than surrounding days
About the same as surrounding days
21% lower than surrounding days
6% lower than surrounding days
About the same as surrounding days
48% 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 McAllen-Edinburg-Mission
Peak-date arrivals · 2020-06-27
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 Jackson
Peak-date arrivals · 2020-06-26
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 Austin-Round Rock
Peak-date arrivals · 2020-06-27
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 Houston-The Woodlands-Sugar Land
Peak-date arrivals · 2020-06-26
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 · 2020-06-27
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 Charleston-North Charleston
Peak-date arrivals · 2020-06-27
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 Columbia
Peak-date arrivals · 2020-06-27
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 Nashville-Davidson--Murfreesboro--Franklin
Peak-date arrivals · 2020-06-27
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 Dallas-Fort Worth-Arlington
Peak-date arrivals · 2020-06-27
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 Little Rock-North Little Rock-Conway
Peak-date arrivals · 2020-06-27
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 Oklahoma City
Peak-date arrivals · 2020-06-27
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 Tulsa
Peak-date arrivals · 2020-06-27
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 Wichita
Peak-date arrivals · 2020-06-28
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 | 64.9 µg/m³ | 3.0 | Jun 27, 2020 | #3 of its top days |
| McAllen-Edinburg-Mission, TX | 64 µg/m³ | 5.5 | Jun 27, 2020 | Worst day on record |
| Austin-Round Rock, TX | 60.3 µg/m³ | 2.7 | Jun 27, 2020 | Worst day on record |
| Dallas-Fort Worth-Arlington, TX | 53.2 µg/m³ | 2.4 | Jun 27, 2020 | #5 of its top days |
| Houston-The Woodlands-Sugar Land, TX | 50.9 µg/m³ | 2.3 | Jun 26, 2020 | #8 of its top days |
| Little Rock-North Little Rock-Conway, AR | 48.1 µg/m³ | 2.2 | Jun 27, 2020 | #4 of its top days |
| Tulsa, OK | 46.2 µg/m³ | 2.1 | Jun 27, 2020 | #5 of its top days |
| Nashville-Davidson--Murfreesboro--Franklin, TN | 43.7 µg/m³ | 2.0 | Jun 27, 2020 | #12 of its top days |
| Oklahoma City, OK | 43.7 µg/m³ | 3.6 | Jun 27, 2020 | #6 of its top days |
| Wichita, KS | 42 µg/m³ | 1.9 | Jun 28, 2020 | #13 of its top days |
| Jackson, MS | 40.7 µg/m³ | 1.9 | Jun 26, 2020 | #6 of its top days |
| Charleston-North Charleston, SC | 40.5 µg/m³ | 1.8 | Jun 27, 2020 | #22 of its top days |
| Columbia, SC | 39.4 µg/m³ | 1.8 | Jun 27, 2020 | #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.
AQS PM2.5 qualifier IA — African Dust.
EPA AQS carries an agency-submitted informational qualifier (IA, African Dust.) on 1 PM2.5 sample in the candidate CBSA on 2020-06-26, identifying windblown or transported dust as affecting the sample. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
AQS PM2.5 qualifier IA — African Dust.
EPA AQS carries an agency-submitted informational qualifier (IA, African Dust.) on 96 PM2.5 samples in the candidate CBSA on 2020-06-26, identifying windblown or transported dust as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
AQS PM2.5 qualifier IA — African Dust.
EPA AQS carries an agency-submitted informational qualifier (IA, African Dust.) on 1 PM2.5 sample in the candidate CBSA on 2020-06-27, identifying windblown or transported dust as affecting the sample. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
AQS PM2.5 qualifier IA — African Dust.
EPA AQS carries an agency-submitted informational qualifier (IA, African Dust.) on 5 PM2.5 samples in the candidate CBSA on 2020-06-26, identifying windblown or transported dust as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
AQS PM2.5 qualifier IA — African Dust.
EPA AQS carries an agency-submitted informational qualifier (IA, African Dust.) on 92 PM2.5 samples in the candidate CBSA on 2020-06-27, identifying windblown or transported dust as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
AQS PM2.5 qualifier IA — African Dust.
EPA AQS carries an agency-submitted informational qualifier (IA, African Dust.) on 41 PM2.5 samples in the candidate CBSA on 2020-06-27, identifying windblown or transported dust as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
AQS PM2.5 qualifier IA — African Dust.
EPA AQS carries an agency-submitted informational qualifier (IA, African Dust.) on 72 PM2.5 samples in the candidate CBSA on 2020-06-27, identifying windblown or transported dust as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
AQS PM2.5 qualifier IA — African Dust.
EPA AQS carries an agency-submitted informational qualifier (IA, African Dust.) on 1 PM2.5 sample in the candidate CBSA on 2020-06-27, identifying windblown or transported dust as affecting the sample. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
AQS PM2.5 qualifier IA — African Dust.
EPA AQS carries an agency-submitted informational qualifier (IA, African Dust.) on 50 PM2.5 samples in the candidate CBSA on 2020-06-28, identifying windblown or transported dust as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
AQS PM2.5 qualifier IA — African Dust.
EPA AQS carries an agency-submitted informational qualifier (IA, African Dust.) on 22 PM2.5 samples in the candidate CBSA on 2020-06-27, identifying windblown or transported dust as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
An archived NWS Air Quality Alert for Columbia, SC, issued 2020-06-27T18:01Z, explicitly identifies windblown or transported dust. IEM is the archive, not the official system of record.
An archived NWS Air Quality Alert for Charleston-North Charleston, SC, issued 2020-06-27T17:24Z, explicitly identifies windblown or transported dust. IEM is the archive, not the official system of record.
NASA documented the June 2020 Saharan plume reaching the United States and reported unhealthy fine-particle AQI levels in Texas on June 27. This supports regional dust transport, not unique apportionment of the McAllen monitor value.
NOAA's analysis tracked the June 2020 Saharan dust event through Houston, identifying the event period at the Houston-area site as June 26–27 and using surface PM2.5 observations to track transport.
Photos: KSAT viewers send in photos of San Antonio skies as Saharan dust arrives
Contemporaneous San Antonio reporting stated that the visible haze was Saharan dust arriving that weekend.
Saharan dust plume to reach highest levels in San Antonio on Saturday
Contemporaneous San Antonio reporting said TCEQ expected a heavy African dust plume to reach its highest local levels on Saturday, June 27, with particle pollution unhealthy for sensitive groups.
Saharan Dust Cloud Causes North Texas Air To Be Deemed 'Unhealthy'
CBS Texas reported that a historic Saharan dust cloud reached North Texas on June 27 and caused unhealthy air conditions in Dallas-area counties.
Historic Saharan dust event fouls air along Gulf Coast
The opened report uses satellite imagery and surface-air-quality data to describe Saharan dust over Mississippi and specifically forecasts impacts in Jackson on June 26. It supports regional dust transport and air-quality influence but does not quantify dust-attributable PM2.5 at the candidate monitor.
Saharan dust plume could be dangerous for those with a respiratory illness
The opened Nashville report says a Saharan dust plume was expected to produce a weekend air-quality alert in Middle Tennessee and that a significant amount would approach the surface. This supports dust transport for the June 27 candidate but remains partly forecast-based and does not quantify dust-attributable PM2.5.
Cited authorities: Saharan dust plume
Agency determination A government body issued a record naming this cause for this event: an NWS air-quality alert, a NOAA Storm Events record, or a state or local official archive.
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.