372% above nearby days
Fireworks Possible
2013-01-01 Phoenix-Mesa-Scottsdale, AZ fireworks episode
Daily PM2.5 peaked at 97.3 µg/m³ near Phoenix across 1 covered metro home to 5.2 million people.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 3.9 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 20 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 event falls exactly in the versioned New Year or Independence Day window, no competing event-specific cause was recovered, and the national fireworks-PM2.5 signal is well established.
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
97.3 µg/m³ near Phoenix
EPA monitors recorded the event across 1 metro. The peak daily concentration is roughly 4.4 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.
Phoenix-Mesa-Scottsdale, AZ
Monitor comparison window 2012-12-29 to 2013-01-04 · PM2.5 target: SOUTH PHOENIX
23% lower than surrounding days
6% higher than surrounding days
Pollution fingerprint
Metro-wide median of reporting monitors PM2.5 57.3 µg/m³
372% higher than surrounding days
Before14.8 µg/m³ Event57.3 µg/m³ After6.67 µg/m³
PM10 18 µg/m³
6% higher than surrounding days
Before19 µg/m³ Event18 µg/m³ After13 µg/m³
Carbon monoxide 0.579 ppm
18% higher than surrounding days
Before0.540 ppm Event0.579 ppm After0.342 ppm
Nitrogen dioxide 21.7 ppb
10% lower than surrounding days
Before24.2 ppb Event21.7 ppb After24.5 ppb
Sulfur dioxide 1.29 ppb
About the same as surrounding days
Before1.13 ppb Event1.29 ppb After1.65 ppb
Ozone 0.029 ppm
11% higher than surrounding days
Before0.025 ppm Event0.029 ppm After0.034 ppm
Atmospheric conditions
Nearby EPA weather observations46% higher than surrounding days
7% lower than surrounding days
23% 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.
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.
Affected metros
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| Phoenix-Mesa-Scottsdale, AZ | 97.3 µg/m³ | 4.4 | Jan 1, 2013 | #11 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.
Effects of Independence Day fireworks on atmospheric concentrations of fine particulate matter in the United States
NOAA Air Resources Laboratory
A peer-reviewed analysis of 315 U.S. monitors found PM2.5 rose 42 percent on average during Independence Day celebrations, peaking late July 4 and declining the following morning.
What it supports
Context for the event; this item does not establish the attributed cause by itself.
Limit
The national multi-year pattern does not independently attribute the supplied local event.
Holiday timing pattern
IAQng deterministic inference policy
The event peak falls on 2013-01-01 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.
What remains uncertain
- No exact local official attribution was recovered, so confidence remains possible.
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.