Mixed causes Likely
Daily PM2.5 peaked at 152.1 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 ≈ 5.4 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 34 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
Independent exact-date reporting attributes the Phoenix and Tucson New Year's Day PM2.5 episodes to holiday fireworks and wood burning, with stagnant or inverted conditions allowing pollution to accumulate.
Likely Applicable reporting or a supported inference makes this the best current causal explanation.
KGUN 9 Tucson · Jan 1, 2016 corroborates
Tucson-area monitors recorded elevated fine particles after New Year's celebrations, and the report says the increase was most likely caused by fireworks and wood burning.
FOX 10 Phoenix · Jan 1, 2016 corroborates
Maricopa County's air-quality spokesman attributed the New Year's Day haze to heavy wood burning, fireworks, weak winds, and an inversion that held pollution near the surface.
KJZZ · Jan 1, 2016 corroborates
Contemporaneous reporting says Arizona environmental officials expected elevated fine-particle pollution in Phoenix on January 1 and instituted a no-burn day; it does not provide a source attribution for this event.
See every retained source and limitation ↓
Sequence: Phoenix (Jan 1) → Tucson (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
Tucson-area monitors recorded elevated fine particles after New Year's celebrations, and the report says the increase was most likely caused by fireworks and wood burning.
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
Contemporaneous reporting says Arizona environmental officials expected elevated fine-particle pollution in Phoenix on January 1 and instituted a no-burn day; it does not provide a source attribution for this event.
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 “Mixed causes” explanation; it does not assign the cause by itself.
Phoenix-Mesa-Scottsdale, AZ
Monitor comparison window 2015-12-29 to 2016-01-04 · PM2.5 target: WEST PHOENIX
469% above nearby days
38% lower than surrounding days
64% higher than surrounding days
469% higher than surrounding days
64% higher than surrounding days
90% higher than surrounding days
About the same as surrounding days
56% higher than surrounding days
6% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
38% lower than surrounding days
Tucson, AZ
Monitor comparison window 2015-12-29 to 2016-01-04 · PM2.5 target: ORANGE GROVE
145% above nearby days
About the same as surrounding days
93% higher than surrounding days
145% higher than surrounding days
93% higher than surrounding days
13% higher than surrounding days
About the same as surrounding days
157% higher than surrounding days
8% higher than surrounding days
About the same as surrounding days
About the same as surrounding days
About the same as 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 | 152.1 µg/m³ | 6.9 | Jan 1, 2016 | #2 of its top days |
| Tucson, AZ | 27.9 µg/m³ | 1.3 | Jan 1, 2016 | #12 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.
KGUN 9 Tucson
Tucson-area monitors recorded elevated fine particles after New Year's celebrations, and the report says the increase was most likely caused by fireworks and wood burning.
A retained source supports the attributed cause for the stated place and dates.
The report identifies a mixed holiday-combustion cause rather than quantifying the separate contributions from fireworks and wood burning.
FOX 10 Phoenix
Maricopa County's air-quality spokesman attributed the New Year's Day haze to heavy wood burning, fireworks, weak winds, and an inversion that held pollution near the surface.
A retained source supports the attributed cause for the stated place and dates.
The report applies to metropolitan Phoenix and does not establish Tucson's cause.
IAQng deterministic inference policy
The event peak falls on 2016-01-01 and the event lasts no more than two days. Under holiday_fireworks_possible.v1, that timing is consistent with a possible fireworks contribution.
A possible fireworks contribution; this is a reproducible inference, not direct occurrence or causal evidence.
Pre-event and post-event temporal-shape data were not supplied.
Likely Applicable reporting or a supported inference makes this the best current causal explanation.
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.