Mesa Air Quality in December
Across 2019–2025, Mesa's December air quality had a median AQI of 83 (Moderate) over 217 monitored days in the Phoenix-Mesa-Scottsdale, AZ area. 25.4% of December days (55 of 217) reached Unhealthy for Sensitive Groups or worse, and fine particulate matter (PM2.5) set the daily AQI on 67.7% of days. The cleanest December on record here was 2019 (median AQI 66, 1 day above 100) and the worst was 2021 (median 101, 20 days above 100, peak AQI 140).
- Good: 2.8%
- Moderate: 71.9%
- Unhealthy for Sensitive Groups: 21.7%
- Unhealthy or worse: 3.7%
Reduce Indoor Ozone in Mesa
Today's main pollutant in Mesa is ground-level ozone (AQI 27). Important: standard HEPA filters do NOT remove ozone — only a purifier with a substantial activated-carbon bed adsorbs it. The biggest wins are cutting indoor sources (gas appliances, certain "ionizer" purifiers) and ventilating when outdoor ozone is low (early morning). A high-carbon unit helps with the gases and VOCs that linger indoors.
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How is the air in Mesa in December?
Moderate on a typical day: median AQI 83 across 2019–2025, with 25.4% of December days above AQI 100. Fine particulate matter (PM2.5) is the main driver.
- ✓2.8% of December days were Good (AQI 0–50), 71.9% Moderate (51–100).
- ✓55 days of 217 reached AQI 101+; the December peak was 189.
- ✓Best December: 2019; worst December: 2021.
Frequently asked questions
What is the air quality like in Mesa in December?▾
Across 2019–2025, the median daily AQI in Mesa in December was 83 (Moderate). 2.8% of days were Good, 71.9% Moderate, and 25.4% reached Unhealthy for Sensitive Groups or worse, based on 217 monitored days in EPA's Air Quality System.
Is December a good time for outdoor exercise in Mesa?▾
A typical December day in Mesa is Moderate (median AQI 83): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 4 of December days (25.4%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
Which pollutant causes Mesa's December air quality problems?▾
Fine particulate matter (PM2.5) set the daily AQI on 67.7% of December days in Mesa. The highest December AQI recorded in 2019–2025 was 189 (Unhealthy), in 2021.
Mesa December air quality, year by year
Mesa December air quality by year (Phoenix-Mesa-Scottsdale, AZ, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019cleanest | 31 | 66 | 1 | 133 | PM2.5 |
| 2020 | 31 | 82 | 9 | 161 | PM2.5 |
| 2021worst | 31 | 101 | 20 | 140 | O3 |
| 2022 | 31 | 77 | 6 | 189 | PM2.5 |
| 2023 | 31 | 82 | 4 | 179 | PM2.5 |
| 2024 | 31 | 99 | 14 | 162 | PM10 |
| 2025 | 31 | 77 | 1 | 102 | PM2.5 |
What December air means in Mesa
A typical December day in Mesa is Moderate (median AQI 83): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 4 of December days (25.4%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
December's median AQI of 83 is above Mesa's whole-year median of 79, making it one of the area's dirtier periods. Nationally, the median December AQI across every EPA metro area (95,590 metro-days, 2019–2025) is 39, so Mesa runs above the national December norm; 25.4% of its December days topped AQI 100 versus 0.7% nationally (above average).
December is part of Mesa's winter season (December, January, February); the winter page pools all three months.
Activity-specific thresholds: running, cycling, kids' sports.
Right now in Mesa
The latest EPA AirNow observation puts Mesa's AQI at 27 (O3). The figures above are multi-year month statistics, not today's reading.
View current Mesa air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (Phoenix-Mesa-Scottsdale, AZ), 2019–2025. Daily AQI per CBSA is the highest AQI reported by any monitor in the area that day; the defining parameter is the pollutant that set it. Month and season statistics pool every such day in the period across all years listed. Retrieved 2026-09-09.