Wildfire smoke Agency determination
Daily PM2.5 peaked at 85.9 µg/m³ near Riverside across 2 covered metros home to 7.1 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 ≈ 3.2 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 23 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
The supplied evidence supports wildfire smoke and documents an overlapping or continuing regional occurrence across the proposed members.
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 · Sep 9, 2024 official
EPA AQS carries an agency-submitted informational qualifier (IT, Wildfire-U. S.) on 97 PM2.5 samples in the candidate CBSA on 2024-09-09, identifying wildfire smoke 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 · Sep 11, 2024 official
EPA AQS carries an agency-submitted informational qualifier (IT, Wildfire-U. S.) on 336 PM2.5 samples in the candidate CBSA on 2024-09-11, identifying wildfire smoke as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
South Coast Air Quality Management District via NWS · Sep 9, 2024 official
South Coast AQMD explicitly attributed increased fine-particle pollution in the Riverside event area to wildfire smoke. IEM is the archive, not the official system of record.
See every retained source and limitation ↓
Sequence: Riverside (Sep 9) → Las Vegas (Sep 11)
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 (IT, Wildfire-U. S.) on 97 PM2.5 samples in the candidate CBSA on 2024-09-09, identifying wildfire smoke as affecting the samples. An informational qualifier is an official…
View supporting source ↗Air-mass movement
Clark County reported that smoke from Southern California wildfires was lingering in the Las Vegas Valley and elevating particulate matter.
View transport source ↗Local response
EPA monitors recorded the event across 2 metros. The peak daily concentration is roughly 3.9 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.
Riverside-San Bernardino-Ontario, CA
Monitor comparison window 2024-09-06 to 2024-09-12 · PM2.5 target: Big Bear
189% above nearby days
About the same as surrounding days
About the same as surrounding days
189% higher than surrounding days
About the same as surrounding days
64% higher than surrounding days
13% higher than surrounding days
25% higher than surrounding days
11% higher 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
Las Vegas-Henderson-Paradise, NV
Monitor comparison window 2024-09-08 to 2024-09-14 · PM2.5 target: Garrett Jr. High
430% above nearby days
125% higher than surrounding days
150% higher than surrounding days
430% higher than surrounding days
150% higher than surrounding days
27% higher than surrounding days
55% lower than surrounding days
About the same as surrounding days
14% higher than surrounding days
40% lower than surrounding days
About the same as surrounding days
About the same as surrounding days
125% 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.
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 |
|---|---|---|---|---|
| Riverside-San Bernardino-Ontario, CA | 85.9 µg/m³ | 3.9 | Sep 9, 2024 | #18 of its top days |
| Las Vegas-Henderson-Paradise, NV | 83.3 µg/m³ | 3.8 | Sep 11, 2024 | #3 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 IT — Wildfire-U. S.
EPA AQS carries an agency-submitted informational qualifier (IT, Wildfire-U. S.) on 97 PM2.5 samples in the candidate CBSA on 2024-09-09, identifying wildfire smoke 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 IT — Wildfire-U. S.
EPA AQS carries an agency-submitted informational qualifier (IT, Wildfire-U. S.) on 336 PM2.5 samples in the candidate CBSA on 2024-09-11, identifying wildfire smoke as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
Archived Riverside-area Air Quality Alert, September 9, 2024
South Coast AQMD explicitly attributed increased fine-particle pollution in the Riverside event area to wildfire smoke. IEM is the archive, not the official system of record.
Riverside County Health Officials Urge Residents to Take Precautions Due to Smoke and Ash from Fires
Riverside County stated that Southern California wildfires were generating smoke and ash over parts of the county during the event period.
Air Quality Alert for Wildfire Smoke Issued Through and Friday
Clark County reported that smoke from Southern California wildfires was lingering in the Las Vegas Valley and elevating particulate matter.
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.