Fireworks
Fireworks episode, 2017-12-31 through 2018-01-01
Daily PM2.5 peaked at 134.1 µg/m³ near Phoenix across 2 covered metros home to 6.3 million people. 2 metros 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 ≈ 7.4 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 46 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
Qualified frozen evidence supports fireworks as the broad cause for this time-bounded episode.
Sequence: Phoenix (Dec 31) → Tucson (Dec 31)
Affected metros
| Metro | Peak PM2.5 | Cigarettes, whole event | Peak day | All-time standing |
|---|---|---|---|---|
| Phoenix-Mesa-Scottsdale, AZ | 134.1 µg/m³ | 9.5 | Jan 1, 2018 | #4 of its top days |
| Tucson, AZ | 41.2 µg/m³ | 2.9 | Jan 1, 2018 | #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.
The evidence
EPA AQS monitor qualifier 1
- AQS PM2.5 qualifier RH — Fireworks. EPA AQS carries an agency-submitted request-exclusion qualifier (RH, Fireworks.) on 192 PM2.5 samples in the candidate CBSA on 2018-01-01, 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.
Agency and publisher pages 1
- Cracking the AQ Code ADEQ attributed the Phoenix holiday PM2.5 episode to calm conditions and seasonal emissions: fireplace use at Christmas and an additional fireworks contribution on New Year's Eve. It reported record PM2.5 AQI values for both New Year's Eve and New Year's Day.
What remains uncertain
- AQS qualifiers are submitting-agency causal flags and do not by themselves establish EPA concurrence.
- The evidence resolves the broad cause but does not require a named fire, facility, or incident.
- The retained official evidence directly attributes the Phoenix portion; it does not independently establish the Tucson portion.
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.