SmogRank / World / United States / California / September 2025

Most polluted cities in California, United States, September 2025

123 cities in California, United States ranked by their average PM2.5 over the 30 days. Worst: Mammoth Lakes at 28.0 µg/m³, #106 of 3,052 cities in the world. Cleanest: Sebastopol at 3.3. A city needs measurements on 70% of the days to be ranked.

Ranked by unhealthy days: the share of each city's measured days with a daily mean over 35.4 µg/m³ (US AQI 101+), Unhealthy for Sensitive Groups or worse on the US EPA's scale. Ties go to the higher average.

← Mammoth Lakes 24% 20%0
Every city in California, United States ranked for September 2025, one column each, ranked by unhealthy days: height is the share of its measured days that were unhealthy, colour its average. Point at it to read a city; tap to open it.
  1. 1Mammoth Lakes
    24%
  2. 2Yreka
    7%
  3. 3Bakersfield
    0%
  4. 4Riverside
    0%
  5. 5Porterville
    0%
  6. 6Corcoran
    0%
  7. 7Rio Vista
    0%
  8. 8Glendora
    0%
  9. 9Hawthornelow-cost sensors
    0%
  10. 10Visalia
    0%
  11. 11Carsonlow-cost sensors
    0%
  12. 12Jurupa Valley
    0%
  13. 13Hanford
    0%
  14. 14Berkeley
    0%
  15. 15Santa Monicalow-cost sensors
    0%
  16. 16Inglewoodlow-cost sensors
    0%
  17. 17Fontana
    0%
  18. 17Long Beach
    0%
  19. 17Madera
    0%
  20. 20Torrancelow-cost sensors
    0%
  21. 21Lomitalow-cost sensors
    0%
  22. 22Fresno
    0%
  23. 23Los Angeles
    0%
  24. 24Imperial Beach
    0%
  25. 24Willows
    0%
  26. 26Woodland
    0%
  27. 27Oceanside
    0%
  28. 28Agouralow-cost sensors
    0%
  29. 28Colusa
    0%
  30. 30Compton
    0%
  31. 30Victorville
    0%
  32. 32San Diego
    0%
  33. 33San Jose
    0%
  34. 34North Auburn
    0%
  35. 34Santa Barbara
    0%
  36. 36Richmond
    0%
  37. 37Clovis
    0%
  38. 37Tracy
    0%
  39. 39Anaheim
    0%
  40. 39Burbank
    0%
  41. 41Poway
    0%
  42. 42Huron
    0%
  43. 43Merced
    0%
  44. 43Santa Paula
    0%
  45. 45Folsom
    0%
  46. 45Turlock
    0%
  47. 45Vallejo
    0%
  48. 45La Crescenta-Montroselow-cost sensors
    0%
  49. 49Lincoln
    0%
  50. 49Santa Clarita
    0%
  51. 51Stockton
    0%
  52. 52Lompoc
    0%
  53. 52Prunedalelow-cost sensors
    0%
  54. 52Simi Valley
    0%
  55. 52Yuba City
    0%
  56. 56El Cajon
    0%
  57. 56Oceano
    0%
  58. 58Florinlow-cost sensors
    0%
  59. 58Lake Elsinore
    0%
  60. 58Modesto
    0%
  61. 58Oakland
    0%
  62. 58Thousand Oaks
    0%
  63. 63Banning
    0%
  64. 63El Rio
    0%
  65. 63Goletalow-cost sensors
    0%
  66. 63Roseville
    0%
  67. 63San Leandro
    0%
  68. 63Redding
    0%
  69. 69Davis
    0%
  70. 69Galt
    0%
  71. 69Red Bluff
    0%
  72. 72Salinas
    0%
  73. 72San Francisco
    0%
  74. 72Windsorlow-cost sensors
    0%
  75. 75Vacaville
    0%
  76. 76Chico
    0%
  77. 76Gridley
    0%
  78. 76San Luis Obispo
    0%
  79. 79Brawley
    0%
  80. 79Martinez
    0%
  81. 79Watsonvillelow-cost sensors
    0%
  82. 82Alta Sierra
    0%
  83. 82Calexico
    0%
  84. 82Seasidelow-cost sensors
    0%
  85. 85El Centro
    0%
  86. 85Hollister
    0%
  87. 85Live Oaklow-cost sensors
    0%
  88. 88Carpinteria
    0%
  89. 88Crestline
    0%
  90. 88Manteca
    0%
  91. 91South San Franciscolow-cost sensors
    0%
  92. 91Ukiah
    0%
  93. 93Ojai
    0%
  94. 93Rancho Murieta
    0%
  95. 95Gilroy
    0%
  96. 95Palo Altolow-cost sensors
    0%
  97. 95Truckee
    0%
  98. 95Crescent City
    0%
  99. 95Arden-Arcade
    0%
  100. 100Fillmore
    0%
  101. 100Indio
    0%
  102. 100King City
    0%
  103. 103Alpine
    0%
  104. 103Sacramento
    0%
  105. 105Grass Valley
    0%
  106. 105Lancaster
    0%
  107. 105Pleasanton
    0%
  108. 108Guadalupe
    0%
  109. 108Redwood City
    0%
  110. 110Santa Cruz
    0%
  111. 111Temecula
    0%
  112. 112Big Bear City
    0%
  113. 112Paradise
    0%
  114. 114Concord
    0%
  115. 115Atascadero
    0%
  116. 115San Rafael
    0%
  117. 117Ben Lomond
    0%
  118. 117Livermore
    0%
  119. 119Sunnyvalelow-cost sensors
    0%
  120. 120Solvang
    0%
  121. 121Ridgecrest
    0%
  122. 122Orcutt
    0%
  123. 122Sebastopol
    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, September 2025 · All cities in United States, September 2025 · California now

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SmogRank, most polluted cities in California, United States, PM2.5, September 2025, smogrank.com/us/region/california/history/2025-09 (accessed 7 Oct 2026).

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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.