29% above nearby days
Fireworks Possible
1999-07-05 Nashville-Davidson--Murfreesboro--Franklin, TN fireworks episode
Daily PM2.5 peaked at 55.8 µg/m³ near Nashville across 1 covered metro home to 2.2 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 ≈ 2.1 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 4.4 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”
The PM2.5 event falls on a major fireworks holiday; no exact local attribution was recovered, so the hypothesis remains explicitly possible.
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
Inference, not direct attribution
Holiday timing: The event falls in the July 3–5 or December 31–January 1 fireworks window. That makes fireworks a reasonable hypothesis, but no retained source directly attributes this event.
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.
- 1Inferred
Source or mechanism
Pattern-based explanation
Holiday timing. The event falls in the July 3–5 or December 31–January 1 fireworks window. That makes fireworks a reasonable hypothesis, but no retained source directly attributes this event.
- 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
55.8 µg/m³ near Nashville
EPA monitors recorded the event across 1 metro. The peak daily concentration is roughly 2.5 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.
Nashville-Davidson--Murfreesboro--Franklin, TN
Monitor comparison window 1999-07-02 to 1999-07-08 · PM2.5 target: Lockeland
39% higher than surrounding days
Pollution fingerprint
Metro-wide median of reporting monitors PM2.5 32.1 µg/m³
29% higher than surrounding days
Before13.6 µg/m³ Event32.1 µg/m³ After24.8 µg/m³
PM10 46 µg/m³
39% higher than surrounding days
Before26 µg/m³ Event46 µg/m³ After33 µg/m³
Carbon monoxide 0.613 ppm
24% higher than surrounding days
Before0.271 ppm Event0.613 ppm After0.550 ppm
Nitrogen dioxide 9.15 ppb
About the same as surrounding days
Before8.14 ppb Event9.15 ppb After10.6 ppb
Sulfur dioxide 1.75 ppb
About the same as surrounding days
Before1.42 ppb Event1.75 ppb After2.75 ppb
Ozone 0.031 ppm
About the same as surrounding days
Before0.028 ppm Event0.031 ppm After0.045 ppm
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.
—
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 |
|---|---|---|---|---|
| Nashville-Davidson--Murfreesboro--Franklin, TN | 55.8 µg/m³ | 2.5 | Jul 5, 1999 | #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
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.
Holiday timing pattern
IAQng deterministic inference policy
The event peak falls on 1999-07-05 and the event lasts no more than two days. Under holiday_fireworks_possible.v1, that timing is consistent with a possible fireworks contribution.
What it supports
A possible fireworks contribution; this is a reproducible inference, not direct occurrence or causal evidence.
Limit
Pre-event and post-event temporal-shape data were not supplied.
No news search has been run for this episode. Its evidence is agency records only, and an absent article is not a finding that none exists.
What remains uncertain
- The classification is bounded to the retained evidence and does not apportion every source contributing to the daily PM2.5 value.
Status and provenance
Possible This is a transparent hypothesis supported by limited evidence or an explicit inference, not a definitive attribution.
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.