SmogRank / Episodes / United States

California, United States, January 2023

For 4 days, from 25 to 28 January 2023, 9 cities in the United States had PM2.5 at least twice their usual for the time of year. The worst reading was Hanford, California, United States: 37.0 µg/m³ on 28 January, about 2.8× its usual 13.2.

No cause namedWe have no fire or smoke records for these days, so we only say what the measurements show.
Cities reached9in 1 country
Days425 to 28 January 2023
Worst day26 January7 cities counted
Furthest above usual3.1×Corcoran

Day by day

26 January 7 cities at twice their usual or more
MaderaClovisMercedHollisterAtascaderoGilroySan Luis ObispoSalinasMantecaArroyo GrandeNipomoTracyOrcuttSan JoseSanta CruzLivermoreGaltPleasantonLompocRedwood CityFolsomSan LeandroSanta BarbaraConcordArden-ArcadeSacramentoRosevilleOaklandBerkeleyDavisVacavilleLincolnSan FranciscoRichmondVallejoFillmoreWoodlandSan RafaelSanta ClaritaLancasterLa Crescenta-MontroseSanta RosaVictorvilleSummerlin SouthSpring ValleyEnterpriseLas VegasModestoFresnoTurlockBakersfieldStocktonPortervilleVisaliaHanfordCorcoran
22 Jan232425262728293031
Every measured city in the area, coloured by its PM2.5 that day; a dark ring marks a city at twice its usual or more. Bars: cities counted each day, coloured by their median level. Choose a day or press play; without JavaScript, the days link to that day's world ranking.

How it spread

HanfordHanford, 22 January: 20.9 µg/m³, 1.6× usualHanford, 23 January: 19.5 µg/m³, 1.5× usualHanford, 24 January: 27.0 µg/m³, 2.0× usualHanford, 25 January: 27.0 µg/m³, 2.0× usualHanford, 26 January: 32.1 µg/m³, 2.4× usualHanford, 27 January: 33.6 µg/m³, 2.5× usualHanford, 28 January: 37.0 µg/m³, 2.8× usualHanford, 29 January: 15.0 µg/m³, 1.1× usualHanford, 30 January: 7.2 µg/m³, 0.5× usualHanford, 31 January: 14.2 µg/m³, 1.1× usualVisaliaVisalia, 22 January: 25.6 µg/m³, 2.0× usualVisalia, 23 January: 20.0 µg/m³, 1.6× usualVisalia, 24 January: 21.7 µg/m³, 1.7× usualVisalia, 25 January: 30.3 µg/m³, 2.4× usualVisalia, 26 January: 30.6 µg/m³, 2.4× usualVisalia, 27 January: 29.1 µg/m³, 2.3× usualVisalia, 28 January: 35.3 µg/m³, 2.8× usualVisalia, 29 January: 12.1 µg/m³, 1.0× usualVisalia, 30 January: 10.0 µg/m³, 0.8× usualVisalia, 31 January: 17.9 µg/m³, 1.4× usualBakersfieldBakersfield, 22 January: 23.7 µg/m³, 1.9× usualBakersfield, 23 January: 15.1 µg/m³, 1.2× usualBakersfield, 24 January: 18.8 µg/m³, 1.5× usualBakersfield, 25 January: 30.3 µg/m³, 2.4× usualBakersfield, 26 January: 29.6 µg/m³, 2.3× usualBakersfield, 27 January: 27.8 µg/m³, 2.2× usualBakersfield, 28 January: 32.1 µg/m³, 2.5× usualBakersfield, 29 January: 17.0 µg/m³, 1.3× usualBakersfield, 30 January: 6.6 µg/m³, 0.5× usualBakersfield, 31 January: 11.7 µg/m³, 0.9× usualFresnoFresno, 22 January: 24.1 µg/m³, 1.8× usualFresno, 23 January: 26.2 µg/m³, 1.9× usualFresno, 24 January: 26.3 µg/m³, 1.9× usualFresno, 25 January: 29.6 µg/m³, 2.2× usualFresno, 26 January: 29.0 µg/m³, 2.1× usualFresno, 27 January: 27.5 µg/m³, 2.0× usualFresno, 28 January: 32.9 µg/m³, 2.4× usualFresno, 29 January: 19.2 µg/m³, 1.4× usualFresno, 30 January: 7.6 µg/m³, 0.6× usualFresno, 31 January: 16.0 µg/m³, 1.2× usualStocktonStockton, 22 January: 12.2 µg/m³, 1.1× usualStockton, 23 January: 5.6 µg/m³, 0.5× usualStockton, 24 January: no readingStockton, 25 January: 27.0 µg/m³, 2.4× usualStockton, 26 January: 30.8 µg/m³, 2.7× usualStockton, 27 January: 23.9 µg/m³, 2.1× usualStockton, 28 January: 13.4 µg/m³, 1.2× usualStockton, 29 January: 7.4 µg/m³, 0.6× usualStockton, 30 January: 4.4 µg/m³, 0.4× usualStockton, 31 January: 15.5 µg/m³, 1.4× usualPortervillePorterville, 22 January: no readingPorterville, 23 January: 10.8 µg/m³, 1.1× usualPorterville, 24 January: 16.8 µg/m³, 1.7× usualPorterville, 25 January: 26.3 µg/m³, 2.7× usualPorterville, 26 January: 19.8 µg/m³, 2.0× usualPorterville, 27 January: 16.8 µg/m³, 1.7× usualPorterville, 28 January: 20.5 µg/m³, 2.1× usualPorterville, 29 January: 7.8 µg/m³, 0.8× usualPorterville, 30 January: 8.3 µg/m³, 0.9× usualPorterville, 31 January: 10.6 µg/m³, 1.1× usualModestoModesto, 22 January: 16.6 µg/m³, 1.4× usualModesto, 23 January: 7.4 µg/m³, 0.6× usualModesto, 24 January: 22.8 µg/m³, 1.9× usualModesto, 25 January: 24.5 µg/m³, 2.1× usualModesto, 26 January: 28.6 µg/m³, 2.4× usualModesto, 27 January: 27.4 µg/m³, 2.3× usualModesto, 28 January: 20.0 µg/m³, 1.7× usualModesto, 29 January: 11.5 µg/m³, 1.0× usualModesto, 30 January: 3.8 µg/m³, 0.3× usualModesto, 31 January: 10.9 µg/m³, 0.9× usualCorcoranCorcoran, 22 January: 16.0 µg/m³, 1.5× usualCorcoran, 23 January: 16.1 µg/m³, 1.5× usualCorcoran, 24 January: 20.7 µg/m³, 1.9× usualCorcoran, 25 January: 23.3 µg/m³, 2.1× usualCorcoran, 26 January: 27.4 µg/m³, 2.5× usualCorcoran, 27 January: 30.0 µg/m³, 2.8× usualCorcoran, 28 January: 34.2 µg/m³, 3.1× usualCorcoran, 29 January: 9.1 µg/m³, 0.8× usualCorcoran, 30 January: 5.1 µg/m³, 0.5× usualCorcoran, 31 January: 11.0 µg/m³, 1.0× usualTurlockTurlock, 22 January: 8.2 µg/m³, 0.8× usualTurlock, 23 January: 7.4 µg/m³, 0.7× usualTurlock, 24 January: 19.3 µg/m³, 1.8× usualTurlock, 25 January: 23.3 µg/m³, 2.1× usualTurlock, 26 January: 21.3 µg/m³, 2.0× usualTurlock, 27 January: 27.5 µg/m³, 2.5× usualTurlock, 28 January: 16.2 µg/m³, 1.5× usualTurlock, 29 January: 3.8 µg/m³, 0.3× usualTurlock, 30 January: 2.1 µg/m³, 0.2× usualTurlock, 31 January: 6.5 µg/m³, 0.6× usual22 Jan232425262728293031
Every counted city, in the order the episode reached them, 3 days before to 3 after. Each square is a day, coloured by that day's PM2.5; outlined: at twice the city's usual or more.
Good0–50
Moderate51–100
Sensitive groups101–150
Unhealthy151–200
Very unhealthy201–300
Hazardous301+

Every city it reached

CityDaysHighestUsualAbove usual
CorcoranCalifornia, United States3 34.228 January10.93.1×
VisaliaCalifornia, United States4 35.328 January12.52.8×
HanfordCalifornia, United States4 37.028 January13.22.8×
PortervilleCalifornia, United States1 26.325 January9.72.7×
StocktonCalifornia, United States2 30.826 January11.42.7×
BakersfieldCalifornia, United States4 32.128 January12.72.5×
TurlockCalifornia, United States1 27.527 January10.92.5×
ModestoCalifornia, United States2 28.626 January11.72.4×
FresnoCalifornia, United States3 32.928 January13.62.4×

Daily means in µg/m³. Usual: the city's median for this time of year (its days within 21 days of the date, every year, leaving out the week around it). Above usual: its highest day against that.

Against other episodes in the United States

Number 36 of 41 episodes in the United States since our records began, by cities reached.

Bars: cities reached; colour: the level of the episode's highest daily reading. All 41.

Use this page

SmogRank, California, United States, January 2023: 9 cities with PM2.5 at twice their usual or more, 25 to 28 January 2023, smogrank.com/episodes/2023-01-california-united-states (accessed 2 October 2026).

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You're welcome to reuse a single chart, image or figure with this citation and a link. Terms.

An episode is a run of days when many cities close to each other (four or more within 350 km on a day, 8 or more in all) each had a daily PM2.5 mean of at least 25 µg/m³ and at least 2 times their usual for that time of year. Found in our own measurements, not picked by hand. How we find episodes. Values are each city's daily mean of its own monitors; causes are the usual kinds for a pattern like this, not a confirmed source.