Mixed causes
2024-01-01 Phoenix-Mesa-Scottsdale, AZ and Tucson, AZ fireworks and winter inversion episode
Daily PM2.5 peaked at 102.8 µg/m³ near Phoenix across 2 covered metros home to 6.3 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 ≈ 3.6 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 22 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.
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.
What happened, in the record
Official evidence identifies fireworks across the Arizona metros and separately identifies an inversion trapping emissions at the West Phoenix monitor. Both are retained as material components of the episode.
Sequence: Phoenix (Jan 1) → Tucson (Jan 1)
Affected metros
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| Phoenix-Mesa-Scottsdale, AZ | 102.8 µg/m³ | 4.7 | Jan 1, 2024 | #7 of its top days |
| Tucson, AZ | 25.8 µg/m³ | 1.2 | Jan 1, 2024 | #19 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.
The evidence
EPA AQS monitor qualifier 2
- AQS PM2.5 qualifier RH — Fireworks. EPA AQS carries an agency-submitted request-exclusion qualifier (RH, Fireworks.) on 144 PM2.5 samples in the candidate CBSA on 2024-01-01, 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.
- AQS PM2.5 qualifier IH — Fireworks. EPA AQS carries an agency-submitted informational qualifier (IH, Fireworks.) on 10 PM2.5 samples in the candidate CBSA on 2024-01-01, identifying fireworks as affecting the samples. An informational qualifier is an official submitting-agency flag, not a request for exclusion or an EPA-concurred determination.
Agency and publisher pages 1
- Air Quality Update meeting minutes The regional government air-quality update identifies the West Phoenix monitor's January 1, 2024 PM2.5 episode and describes an inversion trapping emissions as a contributing condition.
What remains uncertain
- Agency-submitted AQS qualifiers support attribution but do not by themselves establish EPA concurrence.
Status and provenance
Research preview: this record carries research-only status and its boundaries, cause, and name may change as evidence review completes. Grouping policy common_sense_root_cause_grouping.v2. The cause label reflects the assembled evidence above, not an IAQng detection formula.