SmogRank / Episodes / United States
California, United States, December 2023
For 6 days, from 13 to 18 December 2023, 20 cities in the United States had PM2.5 at least twice their usual for the time of year. The worst reading was Bakersfield, California, United States: 58.6 µg/m³ on 17 December, about 3.2× its usual 18.4.
No cause named We have no fire or smoke records for these days, so we only say what the measurements show.
Cities reached 20 in 1 country
Days 6 13 to 18 December 2023
Worst day 16 December 13 cities counted
Furthest above usual 6.2× Redding
Day by day
Play 16 December 13 cities at twice their usual or more
Folsom Lincoln Roseville Galt Woodland Davis Truckee South Lake Tahoe Paradise Vacaville Tracy Carson City Reno Concord Livermore Spanish Springs Pleasanton San Leandro Richmond Oakland San Rafael Santa Rosa San Francisco Redwood City Gilroy Hollister Santa Cruz Ukiah Salinas Atascadero Altamont San Luis Obispo Arroyo Grande Ashland Nipomo Orcutt Grants Pass Madera Visalia Clovis Porterville Sacramento Fresno Corcoran San Jose Merced Chico Medford Arden-Arcade Turlock Manteca Stockton Bakersfield Modesto Hanford Yuba City Redding 10 Dec 11 12 13 14 15 16 17 18 19 20 21 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
Stockton Stockton, 10 December: 33.4 µg/m³, 2.6× usual Stockton, 11 December: 29.3 µg/m³, 2.3× usual Stockton, 12 December: 22.8 µg/m³, 1.8× usual Stockton, 13 December: 34.7 µg/m³, 2.7× usual Stockton, 14 December: 29.0 µg/m³, 2.2× usual Stockton, 15 December: 36.8 µg/m³, 2.9× usual Stockton, 16 December: 35.4 µg/m³, 2.7× usual Stockton, 17 December: 39.6 µg/m³, 3.1× usual Stockton, 18 December: 21.1 µg/m³, 1.6× usual Stockton, 19 December: 8.2 µg/m³, 0.6× usual Stockton, 20 December: 7.4 µg/m³, 0.6× usual Stockton, 21 December: 10.1 µg/m³, 0.8× usual Arden-Arcade Arden-Arcade, 10 December: 27.4 µg/m³, 2.6× usual Arden-Arcade, 11 December: 22.7 µg/m³, 2.2× usual Arden-Arcade, 12 December: 20.9 µg/m³, 2.0× usual Arden-Arcade, 13 December: 25.8 µg/m³, 2.5× usual Arden-Arcade, 14 December: 27.2 µg/m³, 2.6× usual Arden-Arcade, 15 December: 23.1 µg/m³, 2.2× usual Arden-Arcade, 16 December: 25.8 µg/m³, 2.5× usual Arden-Arcade, 17 December: 29.1 µg/m³, 2.8× usual Arden-Arcade, 18 December: 8.9 µg/m³, 0.8× usual Arden-Arcade, 19 December: 1.9 µg/m³, 0.2× usual Arden-Arcade, 20 December: 7.2 µg/m³, 0.7× usual Arden-Arcade, 21 December: 8.9 µg/m³, 0.8× usual Hanford Hanford, 10 December: 22.6 µg/m³, 1.4× usual Hanford, 11 December: 27.5 µg/m³, 1.7× usual Hanford, 12 December: 30.6 µg/m³, 1.9× usual Hanford, 13 December: 43.1 µg/m³, 2.7× usual Hanford, 14 December: 47.6 µg/m³, 2.9× usual Hanford, 15 December: 53.5 µg/m³, 3.3× usual Hanford, 16 December: 51.9 µg/m³, 3.2× usual Hanford, 17 December: 53.8 µg/m³, 3.3× usual Hanford, 18 December: 45.3 µg/m³, 2.8× usual Hanford, 19 December: 7.7 µg/m³, 0.5× usual Hanford, 20 December: 7.0 µg/m³, 0.4× usual Hanford, 21 December: 8.7 µg/m³, 0.5× usual Fresno Fresno, 10 December: 29.7 µg/m³, 1.6× usual Fresno, 11 December: 30.6 µg/m³, 1.6× usual Fresno, 12 December: 30.3 µg/m³, 1.6× usual Fresno, 13 December: 42.6 µg/m³, 2.2× usual Fresno, 14 December: 39.0 µg/m³, 2.1× usual Fresno, 15 December: 41.7 µg/m³, 2.2× usual Fresno, 16 December: 39.7 µg/m³, 2.1× usual Fresno, 17 December: 46.6 µg/m³, 2.5× usual Fresno, 18 December: 39.9 µg/m³, 2.1× usual Fresno, 19 December: 6.8 µg/m³, 0.4× usual Fresno, 20 December: 5.2 µg/m³, 0.3× usual Fresno, 21 December: 5.9 µg/m³, 0.3× usual Corcoran Corcoran, 10 December: 20.4 µg/m³, 1.4× usual Corcoran, 11 December: 24.4 µg/m³, 1.6× usual Corcoran, 12 December: 25.7 µg/m³, 1.7× usual Corcoran, 13 December: 36.8 µg/m³, 2.5× usual Corcoran, 14 December: no reading Corcoran, 15 December: no reading Corcoran, 16 December: no reading Corcoran, 17 December: no reading Corcoran, 18 December: no reading Corcoran, 19 December: no reading Corcoran, 20 December: 7.5 µg/m³, 0.5× usual Corcoran, 21 December: 5.9 µg/m³, 0.4× usual Visalia Visalia, 10 December: 29.9 µg/m³, 1.8× usual Visalia, 11 December: no reading Visalia, 12 December: no reading Visalia, 13 December: 36.8 µg/m³, 2.2× usual Visalia, 14 December: 36.4 µg/m³, 2.2× usual Visalia, 15 December: 38.5 µg/m³, 2.3× usual Visalia, 16 December: 34.5 µg/m³, 2.1× usual Visalia, 17 December: 36.4 µg/m³, 2.2× usual Visalia, 18 December: 34.7 µg/m³, 2.1× usual Visalia, 19 December: 4.3 µg/m³, 0.3× usual Visalia, 20 December: 4.0 µg/m³, 0.2× usual Visalia, 21 December: 7.8 µg/m³, 0.5× usual Modesto Modesto, 10 December: 20.9 µg/m³, 1.6× usual Modesto, 11 December: 18.9 µg/m³, 1.4× usual Modesto, 12 December: 23.0 µg/m³, 1.7× usual Modesto, 13 December: 32.4 µg/m³, 2.4× usual Modesto, 14 December: 35.2 µg/m³, 2.6× usual Modesto, 15 December: 37.3 µg/m³, 2.8× usual Modesto, 16 December: 41.6 µg/m³, 3.1× usual Modesto, 17 December: 43.3 µg/m³, 3.3× usual Modesto, 18 December: 23.5 µg/m³, 1.8× usual Modesto, 19 December: 7.4 µg/m³, 0.6× usual Modesto, 20 December: 6.2 µg/m³, 0.5× usual Modesto, 21 December: 8.9 µg/m³, 0.7× usual Clovis Clovis, 10 December: 20.4 µg/m³, 1.5× usual Clovis, 11 December: 18.9 µg/m³, 1.4× usual Clovis, 12 December: 23.5 µg/m³, 1.8× usual Clovis, 13 December: 29.8 µg/m³, 2.3× usual Clovis, 14 December: 30.0 µg/m³, 2.3× usual Clovis, 15 December: 22.7 µg/m³, 1.7× usual Clovis, 16 December: 21.4 µg/m³, 1.6× usual Clovis, 17 December: 21.2 µg/m³, 1.6× usual Clovis, 18 December: 30.9 µg/m³, 2.3× usual Clovis, 19 December: 2.4 µg/m³, 0.2× usual Clovis, 20 December: 2.7 µg/m³, 0.2× usual Clovis, 21 December: 7.3 µg/m³, 0.6× usual Turlock Turlock, 10 December: 21.5 µg/m³, 1.5× usual Turlock, 11 December: 19.3 µg/m³, 1.4× usual Turlock, 12 December: 16.3 µg/m³, 1.2× usual Turlock, 13 December: 28.2 µg/m³, 2.0× usual Turlock, 14 December: 32.9 µg/m³, 2.4× usual Turlock, 15 December: 34.8 µg/m³, 2.5× usual Turlock, 16 December: 41.0 µg/m³, 2.9× usual Turlock, 17 December: 37.0 µg/m³, 2.6× usual Turlock, 18 December: 24.2 µg/m³, 1.7× usual Turlock, 19 December: 4.2 µg/m³, 0.3× usual Turlock, 20 December: 4.7 µg/m³, 0.3× usual Turlock, 21 December: 11.1 µg/m³, 0.8× usual Bakersfield Bakersfield, 10 December: 30.6 µg/m³, 1.7× usual Bakersfield, 11 December: 29.2 µg/m³, 1.6× usual Bakersfield, 12 December: 34.4 µg/m³, 1.9× usual Bakersfield, 13 December: 33.1 µg/m³, 1.8× usual Bakersfield, 14 December: 40.3 µg/m³, 2.2× usual Bakersfield, 15 December: 38.7 µg/m³, 2.1× usual Bakersfield, 16 December: 51.9 µg/m³, 2.8× usual Bakersfield, 17 December: 58.6 µg/m³, 3.2× usual Bakersfield, 18 December: 31.0 µg/m³, 1.7× usual Bakersfield, 19 December: 20.7 µg/m³, 1.1× usual Bakersfield, 20 December: 13.6 µg/m³, 0.7× usual Bakersfield, 21 December: 5.7 µg/m³, 0.3× usual Manteca Manteca, 10 December: 16.3 µg/m³, 1.3× usual Manteca, 11 December: 11.3 µg/m³, 0.9× usual Manteca, 12 December: 13.6 µg/m³, 1.1× usual Manteca, 13 December: 23.8 µg/m³, 1.9× usual Manteca, 14 December: 30.4 µg/m³, 2.5× usual Manteca, 15 December: 31.6 µg/m³, 2.5× usual Manteca, 16 December: 36.0 µg/m³, 2.9× usual Manteca, 17 December: 38.1 µg/m³, 3.1× usual Manteca, 18 December: 21.0 µg/m³, 1.7× usual Manteca, 19 December: 7.7 µg/m³, 0.6× usual Manteca, 20 December: 5.8 µg/m³, 0.5× usual Manteca, 21 December: 8.1 µg/m³, 0.7× usual Merced Merced, 10 December: 17.6 µg/m³, 1.2× usual Merced, 11 December: 16.1 µg/m³, 1.1× usual Merced, 12 December: 16.3 µg/m³, 1.2× usual Merced, 13 December: 24.0 µg/m³, 1.7× usual Merced, 14 December: 30.3 µg/m³, 2.1× usual Merced, 15 December: 36.5 µg/m³, 2.6× usual Merced, 16 December: 27.4 µg/m³, 1.9× usual Merced, 17 December: 27.5 µg/m³, 2.0× usual Merced, 18 December: 28.6 µg/m³, 2.0× usual Merced, 19 December: 2.7 µg/m³, 0.2× usual Merced, 20 December: 3.5 µg/m³, 0.2× usual Merced, 21 December: 10.8 µg/m³, 0.8× usual Sacramento Sacramento, 10 December: 15.6 µg/m³, 1.5× usual Sacramento, 11 December: 13.1 µg/m³, 1.3× usual Sacramento, 12 December: 17.8 µg/m³, 1.8× usual Sacramento, 13 December: 22.7 µg/m³, 2.2× usual Sacramento, 14 December: 25.2 µg/m³, 2.5× usual Sacramento, 15 December: 17.4 µg/m³, 1.7× usual Sacramento, 16 December: 20.7 µg/m³, 2.0× usual Sacramento, 17 December: 23.3 µg/m³, 2.3× usual Sacramento, 18 December: 10.7 µg/m³, 1.1× usual Sacramento, 19 December: 3.3 µg/m³, 0.3× usual Sacramento, 20 December: 4.8 µg/m³, 0.5× usual Sacramento, 21 December: 7.8 µg/m³, 0.8× usual Madera Madera, 10 December: 16.8 µg/m³, 1.2× usual Madera, 11 December: 13.1 µg/m³, 1.0× usual Madera, 12 December: 15.8 µg/m³, 1.2× usual Madera, 13 December: 25.0 µg/m³, 1.8× usual Madera, 14 December: 27.8 µg/m³, 2.0× usual Madera, 15 December: 28.6 µg/m³, 2.1× usual Madera, 16 December: 22.2 µg/m³, 1.6× usual Madera, 17 December: 21.3 µg/m³, 1.6× usual Madera, 18 December: 30.7 µg/m³, 2.3× usual Madera, 19 December: 2.4 µg/m³, 0.2× usual Madera, 20 December: 2.7 µg/m³, 0.2× usual Madera, 21 December: 5.8 µg/m³, 0.4× usual San Jose San Jose, 10 December: 16.8 µg/m³, 1.6× usual San Jose, 11 December: 14.9 µg/m³, 1.4× usual San Jose, 12 December: 11.4 µg/m³, 1.1× usual San Jose, 13 December: 16.9 µg/m³, 1.6× usual San Jose, 14 December: 18.9 µg/m³, 1.8× usual San Jose, 15 December: 25.2 µg/m³, 2.4× usual San Jose, 16 December: 26.8 µg/m³, 2.6× usual San Jose, 17 December: 23.2 µg/m³, 2.2× usual San Jose, 18 December: 8.1 µg/m³, 0.8× usual San Jose, 19 December: 2.1 µg/m³, 0.2× usual San Jose, 20 December: 3.6 µg/m³, 0.3× usual San Jose, 21 December: 10.9 µg/m³, 1.0× usual Medford Medford, 10 December: 18.2 µg/m³, 1.7× usual Medford, 11 December: 14.7 µg/m³, 1.4× usual Medford, 12 December: 9.6 µg/m³, 0.9× usual Medford, 13 December: 12.3 µg/m³, 1.2× usual Medford, 14 December: 18.1 µg/m³, 1.7× usual Medford, 15 December: 22.1 µg/m³, 2.1× usual Medford, 16 December: 28.0 µg/m³, 2.6× usual Medford, 17 December: 29.9 µg/m³, 2.8× usual Medford, 18 December: 11.7 µg/m³, 1.1× usual Medford, 19 December: 4.9 µg/m³, 0.5× usual Medford, 20 December: 8.5 µg/m³, 0.8× usual Medford, 21 December: 10.2 µg/m³, 1.0× usual Yuba City Yuba City, 10 December: 24.7 µg/m³, 3.2× usual Yuba City, 11 December: 22.5 µg/m³, 2.9× usual Yuba City, 12 December: 14.7 µg/m³, 1.9× usual Yuba City, 13 December: 16.2 µg/m³, 2.1× usual Yuba City, 14 December: 17.0 µg/m³, 2.2× usual Yuba City, 15 December: 17.5 µg/m³, 2.3× usual Yuba City, 16 December: 27.7 µg/m³, 3.6× usual Yuba City, 17 December: 18.2 µg/m³, 2.4× usual Yuba City, 18 December: 8.7 µg/m³, 1.1× usual Yuba City, 19 December: 3.6 µg/m³, 0.5× usual Yuba City, 20 December: 4.4 µg/m³, 0.6× usual Yuba City, 21 December: 10.2 µg/m³, 1.3× usual Chico Chico, 10 December: 21.7 µg/m³, 2.4× usual Chico, 11 December: 19.0 µg/m³, 2.1× usual Chico, 12 December: 18.3 µg/m³, 2.0× usual Chico, 13 December: 18.6 µg/m³, 2.0× usual Chico, 14 December: 20.2 µg/m³, 2.2× usual Chico, 15 December: 23.4 µg/m³, 2.6× usual Chico, 16 December: 25.0 µg/m³, 2.7× usual Chico, 17 December: 17.3 µg/m³, 1.9× usual Chico, 18 December: 7.5 µg/m³, 0.8× usual Chico, 19 December: 2.6 µg/m³, 0.3× usual Chico, 20 December: 4.2 µg/m³, 0.5× usual Chico, 21 December: 9.3 µg/m³, 1.0× usual Redding Redding, 10 December: 13.8 µg/m³, 1.9× usual Redding, 11 December: 18.5 µg/m³, 2.5× usual Redding, 12 December: 8.3 µg/m³, 1.1× usual Redding, 13 December: 5.2 µg/m³, 0.7× usual Redding, 14 December: 12.1 µg/m³, 1.6× usual Redding, 15 December: 10.5 µg/m³, 1.4× usual Redding, 16 December: 13.4 µg/m³, 1.8× usual Redding, 17 December: 45.9 µg/m³, 6.2× usual Redding, 18 December: 8.1 µg/m³, 1.1× usual Redding, 19 December: 2.8 µg/m³, 0.4× usual Redding, 20 December: 3.9 µg/m³, 0.5× usual Redding, 21 December: 9.4 µg/m³, 1.3× usual Porterville Porterville, 10 December: 16.7 µg/m³, 1.5× usual Porterville, 11 December: 19.0 µg/m³, 1.7× usual Porterville, 12 December: 23.7 µg/m³, 2.1× usual Porterville, 13 December: 24.7 µg/m³, 2.2× usual Porterville, 14 December: 18.9 µg/m³, 1.7× usual Porterville, 15 December: 17.7 µg/m³, 1.6× usual Porterville, 16 December: 18.9 µg/m³, 1.7× usual Porterville, 17 December: 26.4 µg/m³, 2.4× usual Porterville, 18 December: 21.1 µg/m³, 1.9× usual Porterville, 19 December: 3.7 µg/m³, 0.3× usual Porterville, 20 December: 5.1 µg/m³, 0.5× usual Porterville, 21 December: 7.1 µg/m³, 0.6× usual 10 Dec 12 14 16 18 20 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. Good 0–50
Moderate 51–100
Sensitive groups 101–150
Unhealthy 151–200
Very unhealthy 201–300
Hazardous 301+
Every city it reached
City Days Highest Usual Above usual
Redding California, United States 1 17 December 7.4 6.2× Yuba City California, United States 1 16 December 7.7 3.6× Hanford California, United States 6 17 December 16.2 3.3× Modesto California, United States 5 17 December 13.3 3.3× Bakersfield California, United States 4 17 December 18.4 3.2× Manteca California, United States 4 17 December 12.4 3.1× Stockton California, United States 5 17 December 12.9 3.1× Turlock California, United States 5 16 December 14.0 2.9× Medford Oregon, United States 2 17 December 10.6 2.8× Arden-Arcade California, United States 4 17 December 10.5 2.8× Chico California, United States 1 16 December 9.1 2.7× Merced California, United States 4 15 December 14.1 2.6× San Jose California, United States 2 16 December 10.5 2.6× Sacramento California, United States 1 14 December 10.1 2.5× Corcoran California, United States 1 13 December 14.8 2.5× Fresno California, United States 6 17 December 19.0 2.5× Porterville California, United States 1 17 December 11.2 2.4× Clovis California, United States 3 18 December 13.2 2.3× Visalia California, United States 6 15 December 16.8 2.3× Madera California, United States 2 18 December 13.6 2.3×
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 18 of 41 episodes in the United States since our records began, by cities reached.
North-eastern United States and Canada, June and July 2023 279 North-eastern United States and Canada, May and June 2023 260 North-eastern United States and Canada, July 2023 241 North-eastern United States and Canada, June 2023 161 North-western United States and Canada, August 2023 110 North-eastern United States and Canada, July 2023 75 Western United States, September 2023 61 South-eastern United States, October 2023 47 North-eastern United States, July 2023 46 North-western United States and Canada, May 2023 42 Western United States, December 2023 32 Northern United States, January 2023 32 California, United States, December 2023 20 Bars: cities reached; colour: the level of the episode's highest daily reading. All 41 .
Use this page SmogRank, California, United States, December 2023: 20 cities with PM2.5 at twice their usual or more, 13 to 18 December 2023, smogrank.com/episodes/2023-12-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.
