Fireworks EPA monitor flag
Daily PM2.5 peaked at 68.4 µg/m³ near Phoenix across 2 covered metros home to 6.3 million people.
Counting the extra PM2.5 above each metro's typical day, this event handed the average affected resident ≈ 2.3 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 14 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
Qualified supplied evidence supports fireworks as the root cause of this event. The supplied record does not establish a coherent shared occurrence with neighboring candidates, so the episode remains event-specific.
EPA monitor flag EPA attached an exceptional-event qualifier to the affected samples. The agency flagged the measurement itself; no separate agency record describes the event.
U.S. EPA Air Quality System and the submitting air monitoring agency · Dec 31, 2022 official
EPA AQS carries an agency-submitted request-exclusion qualifier (RH, Fireworks.) on 72 PM2.5 samples in the candidate CBSA on 2022-12-31, identifying fireworks as affecting the samples. A request-exclusion qualifier is an official submitting-agency causal claim, but this endpoint does not establish EPA concurrence.
U.S. EPA Air Quality System and the submitting air monitoring agency · Jan 1, 2023 official
EPA AQS carries an agency-submitted request-exclusion qualifier (RH, Fireworks.) on 96 PM2.5 samples in the candidate CBSA on 2023-01-01, identifying fireworks as affecting the samples. A request-exclusion qualifier is an official submitting-agency causal claim, but this endpoint does not establish EPA concurrence.
KGUN 9 corroborates
Reporting on southern Arizona’s post-New-Year monitoring says Pima County Department of Environmental Quality considered fireworks and wood burning the most likely causes of elevated fine particulate levels; this corroborates the Tucson portion but does not isolate fireworks from wood burning.
See every retained source and limitation ↓
Sequence: Tucson (Dec 31) → Phoenix (Jan 1)
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 request-exclusion qualifier (RH, Fireworks.) on 72 PM2.5 samples in the candidate CBSA on 2022-12-31, identifying fireworks as affecting the samples. A request-exclusion qualifier is an official submitting-agency…
View supporting source ↗Air-mass movement
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.
Local response
EPA monitors recorded the event across 2 metros. The peak daily concentration is roughly 3.1 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 “Fireworks” explanation; it does not assign the cause by itself.
Tucson, AZ
Monitor comparison window 2022-12-28 to 2023-01-04 · PM2.5 target: ORANGE GROVE
97% above nearby days
61% higher than surrounding days
21% higher than surrounding days
97% higher than surrounding days
21% higher than surrounding days
6% higher than surrounding days
31% lower than surrounding days
101% higher than surrounding days
20% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
61% higher than surrounding days
Phoenix-Mesa-Scottsdale, AZ
Monitor comparison window 2022-12-28 to 2023-01-04 · PM2.5 target: WEST PHOENIX
188% above nearby days
34% higher than surrounding days
About the same as surrounding days
188% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
27% lower than surrounding days
Adjacent observations available
16% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as surrounding days
34% 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.
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| Phoenix-Mesa-Scottsdale, AZ | 68.4 µg/m³ | 3.1 | Jan 1, 2023 | #19 of its top days |
| Tucson, AZ | 26.4 µg/m³ | 1.2 | Dec 31, 2022 | #18 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 RH — Fireworks.
EPA AQS carries an agency-submitted request-exclusion qualifier (RH, Fireworks.) on 72 PM2.5 samples in the candidate CBSA on 2022-12-31, identifying fireworks as affecting the samples. A request-exclusion qualifier is an official submitting-agency causal claim, but this endpoint does not establish EPA concurrence.
AQS PM2.5 qualifier RH — Fireworks.
EPA AQS carries an agency-submitted request-exclusion qualifier (RH, Fireworks.) on 96 PM2.5 samples in the candidate CBSA on 2023-01-01, identifying fireworks as affecting the samples. A request-exclusion qualifier is an official submitting-agency causal claim, but this endpoint does not establish EPA concurrence.
Air quality monitors catch New Year's celebrations
Reporting on southern Arizona’s post-New-Year monitoring says Pima County Department of Environmental Quality considered fireworks and wood burning the most likely causes of elevated fine particulate levels; this corroborates the Tucson portion but does not isolate fireworks from wood burning.
PM2.5 High Pollution Advisory issued for Saturday, December 31 and Sunday, January 1
ADEQ issued a PM2.5 advisory for the event dates; the advisory is contemporaneous but is prospective and does not itself attribute the observed event to fireworks.
ADEQ wants people to limit fireworks in metro Phoenix because of air quality
Contemporaneous reporting says ADEQ asked metro-Phoenix residents to limit fireworks during the advisory, but this is not a post-event attribution.
EPA monitor flag EPA attached an exceptional-event qualifier to the affected samples. The agency flagged the measurement itself; no separate agency record describes the event.
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.