Puget Sound Clean Air Agency official
2023 Data Summary
The agency’s 2023 monitoring summary identifies July 4 fireworks celebrations among the days on which fine-particle levels exceeded the standard at Puget Sound sites.
Fireworks Documented
2023 July 5 Seattle-Tacoma-Bellevue fireworks episode
Daily PM2.5 peaked at 118.2 µg/m³ near Seattle across 1 covered metro home to 4.1 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 ≈ 5.0 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 21 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 basis for “Fireworks”
Qualified supplied evidence supports fireworks for the July 5 Seattle-Tacoma-Bellevue event. No other supplied event was merged without evidence of the same coherent occurrence.
Documented An agency or publisher page assesses this cause, without an agency record naming the event or an EPA qualifier on the data.
Evidence path
From source to city
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.
- 1Documented
Source or mechanism
Fireworks
The agency’s 2023 monitoring summary identifies July 4 fireworks celebrations among the days on which fine-particle levels exceeded the standard at Puget Sound sites.
View supporting source ↗ - 2Research gap
Air-mass movement
The transport path has not been reconstructed
The retained record does not yet show how air traveled from the proposed source to these metros. A trajectory replay or dated plume analysis belongs here.
- 3Documented
Local response
118.2 µg/m³ near Seattle
EPA monitors recorded the event across 1 metro. The peak daily concentration is roughly 5.4 cigarette-equivalents at the outdoor daily rate.
Inspect the pollutant and weather signals ↓
Event autopsy
What the instruments saw
Before, during, and after the episode: nearby pollutant monitors and surface-weather stations show what changed. This context tests the “Fireworks” explanation; it does not assign the cause by itself.
Seattle-Tacoma-Bellevue, WA
Monitor comparison window 2023-07-02 to 2023-07-08 · PM2.5 target: TACOMA - L STREET
458% above nearby days
About the same as surrounding days
46% higher than surrounding days
Pollution fingerprint
Metro-wide median of reporting monitors PM2.5 43.7 µg/m³
458% higher than surrounding days
Before7.83 µg/m³ Event43.7 µg/m³ After4.90 µg/m³
Carbon monoxide 0.377 ppm
46% higher than surrounding days
Before0.259 ppm Event0.377 ppm After0.228 ppm
Nitrogen dioxide 18.6 ppb
49% higher than surrounding days
Before13.4 ppb Event18.6 ppb After7.92 ppb
Sulfur dioxide 1.17 ppb
37% higher than surrounding days
Before0.854 ppb Event1.17 ppb After0.783 ppb
Ozone 0.037 ppm
16% higher than surrounding days
Before0.032 ppm Event0.037 ppm After0.026 ppm
Atmospheric conditions
Nearby EPA weather observations11% lower than surrounding days
About the same as surrounding days
10% higher than surrounding days
About the same as 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.
Measured daily PM2.5 at EPA monitors, as cigarette-equivalents
EPA monitors sit in metro areas, so the colour clusters there. Land between and beyond
them is unmeasured, not clean: this map shows where IAQng has readings, not the extent
of the smoke.
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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
Camera views near
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.
Affected metros
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| Seattle-Tacoma-Bellevue, WA | 118.2 µg/m³ | 5.4 | Jul 5, 2023 | #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
What supports this account
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.
Agency and publisher pages 1
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The agency’s 2023 monitoring summary identifies July 4 fireworks celebrations among the days on which fine-particle levels exceeded the standard at Puget Sound sites.
Status and provenance
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.