Mixed causes Agency determination
Daily PM2.5 peaked at 101.7 µg/m³ near Phoenix across 1 covered metro home to 5.2 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 ≈ 4.1 cigarettes. Across everyone living in the affected metros, that is the collective equivalent of ≈ 21 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 frozen evidence supports mixed as the broad cause for this time-bounded episode.
Agency determination A government body issued a record naming this cause for this event: an NWS air-quality alert, a NOAA Storm Events record, or a state or local official archive.
Arizona Department of Environmental Quality official
ADEQ explicitly states that the winter 2013-2014 Phoenix record had its two largest PM2.5 spikes on Christmas Day and New Year's Day, then identifies fireworks as contributing to the New Year's pollution together with fireplace use, an overnight inversion, and calm conditions.
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
ADEQ explicitly states that the winter 2013-2014 Phoenix record had its two largest PM2.5 spikes on Christmas Day and New Year's Day, then identifies fireworks as contributing to the New Year's pollution together with fireplace use, an overnight…
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 1 metro. The peak daily concentration is roughly 4.6 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 “Mixed causes” explanation; it does not assign the cause by itself.
Phoenix-Mesa-Scottsdale, AZ
Monitor comparison window 2013-12-29 to 2014-01-04 · PM2.5 target: WEST PHOENIX
252% above nearby days
About the same as surrounding days
15% higher than surrounding days
252% higher than surrounding days
15% higher than surrounding days
22% higher than surrounding days
13% lower than surrounding days
About the same as surrounding days
About the same as surrounding days
13% higher than 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 | 101.7 µg/m³ | 4.6 | Jan 1, 2014 | #9 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.
The regional agency identifies consumer fireworks, winter inversions, and residential wood burning as drivers of New Year's PM2.5 episodes in Phoenix, but this page does not attribute the January 1, 2014 event specifically.
Cracking the AQ Code, Volume 2, Issue 10
ADEQ explicitly states that the winter 2013-2014 Phoenix record had its two largest PM2.5 spikes on Christmas Day and New Year's Day, then identifies fireworks as contributing to the New Year's pollution together with fireplace use, an overnight inversion, and calm conditions.
Agency determination A government body issued a record naming this cause for this event: an NWS air-quality alert, a NOAA Storm Events record, or a state or local official archive.
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.