SmogRank / World / United States / California / January 2023

Most polluted cities in California, United States, January 2023

86 cities in California, United States ranked by their average PM2.5 over the 31 days. Worst: Calexico at 12.8 µg/m³, #317 of 1,225 cities in the world. Cleanest: Tracy at 3.2. A city needs measurements on 70% of the days to be ranked.

OpenAQ's archive, where our readings come from, has almost none for 7 of these 31 days. Cities in the United States and Europe have them from the EPA's and the European Environment Agency's own records of the same monitors; elsewhere a city's average is over its other days. Why.

About 0 people in these 12 cities breathed unhealthy air on an average day of January 2023.

Ranked by people: each city's population times its share of unhealthy days, those with a daily mean over 35.4 µg/m³ (US AQI 101+). That is how many people living there breathed unhealthy air on an average day. Only cities measured at 2 or more places at least 3 km apart are ranked: one monitor shouldn't speak for a whole city. Population is the city itself, not its wider metro area.

← Bakersfield 0 0.750
Every city in California, United States ranked for January 2023 with monitors in two or more places, one column each, ranked by people breathing unhealthy air: height is people on an average day, colour its average. Point at it to read a city; tap to open it.
  1. 1Bakersfield
    0
  2. 2Fresno
    0
  3. 3Los Angeles
    0
  4. 4Carsonlow-cost sensors
    0
  5. 4Merced
    0
  6. 6Torrancelow-cost sensors
    0
  7. 7Inglewoodlow-cost sensors
    0
  8. 8Banning
    0
  9. 9San Jose
    0
  10. 10Santa Monicalow-cost sensors
    0
  11. 11Agouralow-cost sensors
    0
  12. 12La Crescenta-Montroselow-cost sensors
    0

Low-cost sensors: consumer units, counted only in cities with no government-grade monitor; they read close to reference monitors on the whole, but 15 to 25% high in humid air. How we use them.

Good0–50
Moderate51–100
Sensitive groups101–150
Unhealthy151–200
Very unhealthy201–300
Hazardous301+

The US EPA's Air Quality Index for PM2.5 (2024 breakpoints). Show values as: µg/m³ · US AQI · India AQI · China AQI · European AQI · UK DAQI · Canada AQHI+. About the scales

All cities in the world, January 2023 · All cities in United States, January 2023 · California now

Use this board

SmogRank, most polluted cities in California, United States, PM2.5, January 2023, smogrank.com/us/region/california/history/2023-01 (accessed 6 Oct 2026).

Download top 10 (PNG)

You're welcome to reuse a single chart, image or figure with this citation and a link. Terms. Raw monitor readings in bulk are published by OpenAQ, under each provider's licence.