SmogRank / Episodes / United States
Western United States, December 2023
For 6 days, from 24 to 29 December 2023, 32 cities in the United States and Mexico had PM2.5 at least twice their usual for the time of year. The worst reading was Phoenix, Arizona, United States: 71.0 µg/m³ on 25 December, about 4.0× its usual 17.8.
No cause named We have no fire or smoke records for these days, so we only say what the measurements show.
Cities reached 32 in 2 countries
Days 6 24 to 29 December 2023
Worst day 25 December 20 cities counted
Furthest above usual 4.0× Phoenix
Day by day
Play 25 December 20 cities at twice their usual or more
Summerlin South Spring Valley Enterprise Victorville Henderson Lancaster Boulder City Banning Glendora La Crescenta-Montrose Santa Clarita Burbank Lake Elsinore Los Angeles Inglewood Santa Monica Simi Valley Fillmore Agoura Thousand Oaks Mesquite Oceanside Fresno Poway El Cajon Santa Barbara Brawley Chula Vista El Centro Hurricane Mexicali Nipomo Orcutt Arroyo Grande Atascadero Lompoc San Luis Obispo Yuma Cedar City South Lake Tahoe Carson City Reno Spanish Springs Hollister Truckee Gilroy Salinas Tracy Galt Folsom Roseville Livermore San Jose Lincoln Santa Cruz Sacramento Pleasanton Davis Concord San Leandro Woodland Redwood City Vacaville Yuba City Oakland Richmond San Francisco Apache Junction San Rafael Casa Grande Paradise Spanish Fork Orem Marana Corcoran Tijuana Hanford Bakersfield Las Vegas Long Beach Torrance Anaheim Modesto Calexico Manteca Clovis Merced Carson Visalia Porterville Mesa Turlock Madera Compton San Diego Hawthorne Tempe Lomita Chico Jurupa Valley Arden-Arcade Stockton Fontana Riverside Glendale Phoenix 21 Dec 22 23 24 25 26 27 28 29 30 31 1 Jan 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
Calexico Calexico, 21 December: no reading Calexico, 22 December: 4.3 µg/m³, 0.3× usual Calexico, 23 December: 20.9 µg/m³, 1.7× usual Calexico, 24 December: 38.2 µg/m³, 3.1× usual Calexico, 25 December: 31.2 µg/m³, 2.5× usual Calexico, 26 December: 20.6 µg/m³, 1.6× usual Calexico, 27 December: 23.8 µg/m³, 1.9× usual Calexico, 28 December: 20.9 µg/m³, 1.7× usual Calexico, 29 December: 10.6 µg/m³, 0.8× usual Calexico, 30 December: 15.2 µg/m³, 1.2× usual Calexico, 31 December: 13.7 µg/m³, 1.1× usual Calexico, 1 January: 16.7 µg/m³, 1.3× usual Madera Madera, 21 December: 5.8 µg/m³, 0.4× usual Madera, 22 December: 12.5 µg/m³, 0.9× usual Madera, 23 December: 17.9 µg/m³, 1.3× usual Madera, 24 December: 32.1 µg/m³, 2.4× usual Madera, 25 December: 37.3 µg/m³, 2.8× usual Madera, 26 December: 29.6 µg/m³, 2.2× usual Madera, 27 December: 25.0 µg/m³, 1.9× usual Madera, 28 December: 12.3 µg/m³, 0.9× usual Madera, 29 December: 4.8 µg/m³, 0.4× usual Madera, 30 December: 4.1 µg/m³, 0.3× usual Madera, 31 December: 7.0 µg/m³, 0.5× usual Madera, 1 January: 14.1 µg/m³, 1.1× usual Mesa Mesa, 21 December: 6.7 µg/m³, 0.7× usual Mesa, 22 December: 5.1 µg/m³, 0.6× usual Mesa, 23 December: 6.7 µg/m³, 0.7× usual Mesa, 24 December: 32.1 µg/m³, 3.5× usual Mesa, 25 December: 25.5 µg/m³, 2.8× usual Mesa, 26 December: 15.5 µg/m³, 1.7× usual Mesa, 27 December: 11.0 µg/m³, 1.2× usual Mesa, 28 December: 14.7 µg/m³, 1.6× usual Mesa, 29 December: 9.6 µg/m³, 1.1× usual Mesa, 30 December: 5.0 µg/m³, 0.5× usual Mesa, 31 December: 16.9 µg/m³, 1.9× usual Mesa, 1 January: 27.6 µg/m³, 3.0× usual Glendale Glendale, 21 December: 7.6 µg/m³, 0.7× usual Glendale, 22 December: 5.6 µg/m³, 0.5× usual Glendale, 23 December: 8.0 µg/m³, 0.8× usual Glendale, 24 December: 31.9 µg/m³, 3.0× usual Glendale, 25 December: 40.9 µg/m³, 3.9× usual Glendale, 26 December: 19.3 µg/m³, 1.8× usual Glendale, 27 December: 15.6 µg/m³, 1.5× usual Glendale, 28 December: 16.1 µg/m³, 1.5× usual Glendale, 29 December: 8.3 µg/m³, 0.8× usual Glendale, 30 December: 5.7 µg/m³, 0.5× usual Glendale, 31 December: 30.6 µg/m³, 2.9× usual Glendale, 1 January: 45.1 µg/m³, 4.3× usual Stockton Stockton, 21 December: 10.1 µg/m³, 0.8× usual Stockton, 22 December: 11.4 µg/m³, 0.9× usual Stockton, 23 December: 18.5 µg/m³, 1.5× usual Stockton, 24 December: 28.8 µg/m³, 2.3× usual Stockton, 25 December: 39.8 µg/m³, 3.2× usual Stockton, 26 December: 37.0 µg/m³, 3.0× usual Stockton, 27 December: 22.9 µg/m³, 1.9× usual Stockton, 28 December: 16.8 µg/m³, 1.4× usual Stockton, 29 December: 12.6 µg/m³, 1.0× usual Stockton, 30 December: 7.1 µg/m³, 0.6× usual Stockton, 31 December: 17.5 µg/m³, 1.4× usual Stockton, 1 January: 12.0 µg/m³, 1.0× usual Arden-Arcade Arden-Arcade, 21 December: 8.9 µg/m³, 0.9× usual Arden-Arcade, 22 December: 11.0 µg/m³, 1.2× usual Arden-Arcade, 23 December: 20.2 µg/m³, 2.1× usual Arden-Arcade, 24 December: 27.8 µg/m³, 3.0× usual Arden-Arcade, 25 December: 28.8 µg/m³, 3.1× usual Arden-Arcade, 26 December: 30.1 µg/m³, 3.2× usual Arden-Arcade, 27 December: 15.6 µg/m³, 1.7× usual Arden-Arcade, 28 December: 6.8 µg/m³, 0.7× usual Arden-Arcade, 29 December: 7.3 µg/m³, 0.8× usual Arden-Arcade, 30 December: 6.4 µg/m³, 0.7× usual Arden-Arcade, 31 December: 6.0 µg/m³, 0.6× usual Arden-Arcade, 1 January: 8.4 µg/m³, 0.9× usual Turlock Turlock, 21 December: 11.1 µg/m³, 0.9× usual Turlock, 22 December: 13.7 µg/m³, 1.1× usual Turlock, 23 December: 10.4 µg/m³, 0.8× usual Turlock, 24 December: 26.4 µg/m³, 2.1× usual Turlock, 25 December: 28.4 µg/m³, 2.2× usual Turlock, 26 December: 32.7 µg/m³, 2.6× usual Turlock, 27 December: 35.4 µg/m³, 2.8× usual Turlock, 28 December: 15.1 µg/m³, 1.2× usual Turlock, 29 December: 10.0 µg/m³, 0.8× usual Turlock, 30 December: 4.7 µg/m³, 0.4× usual Turlock, 31 December: 10.8 µg/m³, 0.9× usual Turlock, 1 January: 10.0 µg/m³, 0.8× usual Phoenix Phoenix, 21 December: 7.7 µg/m³, 0.4× usual Phoenix, 22 December: 6.7 µg/m³, 0.4× usual Phoenix, 23 December: 7.5 µg/m³, 0.4× usual Phoenix, 24 December: 34.1 µg/m³, 1.9× usual Phoenix, 25 December: 71.0 µg/m³, 4.0× usual Phoenix, 26 December: 29.5 µg/m³, 1.7× usual Phoenix, 27 December: 17.5 µg/m³, 1.0× usual Phoenix, 28 December: 22.3 µg/m³, 1.3× usual Phoenix, 29 December: 19.3 µg/m³, 1.1× usual Phoenix, 30 December: 8.2 µg/m³, 0.5× usual Phoenix, 31 December: 25.3 µg/m³, 1.4× usual Phoenix, 1 January: 103.0 µg/m³, 5.8× usual Compton Compton, 21 December: 4.6 µg/m³, 0.3× usual Compton, 22 December: 6.0 µg/m³, 0.3× usual Compton, 23 December: 16.7 µg/m³, 0.9× usual Compton, 24 December: 35.0 µg/m³, 1.9× usual Compton, 25 December: 51.9 µg/m³, 2.9× usual Compton, 26 December: 25.2 µg/m³, 1.4× usual Compton, 27 December: 23.3 µg/m³, 1.3× usual Compton, 28 December: 22.1 µg/m³, 1.2× usual Compton, 29 December: 24.8 µg/m³, 1.4× usual Compton, 30 December: 8.3 µg/m³, 0.5× usual Compton, 31 December: 26.0 µg/m³, 1.4× usual Compton, 1 January: 34.3 µg/m³, 1.9× usual Hawthorne Hawthorne, 21 December: 3.9 µg/m³, 0.2× usual Hawthorne, 22 December: 4.1 µg/m³, 0.3× usual Hawthorne, 23 December: 11.8 µg/m³, 0.7× usual Hawthorne, 24 December: 24.2 µg/m³, 1.5× usual Hawthorne, 25 December: 47.6 µg/m³, 3.0× usual Hawthorne, 26 December: 30.5 µg/m³, 1.9× usual Hawthorne, 27 December: 22.0 µg/m³, 1.4× usual Hawthorne, 28 December: 22.9 µg/m³, 1.4× usual Hawthorne, 29 December: 22.5 µg/m³, 1.4× usual Hawthorne, 30 December: 8.1 µg/m³, 0.5× usual Hawthorne, 31 December: 16.1 µg/m³, 1.0× usual Hawthorne, 1 January: 23.4 µg/m³, 1.5× usual Carson Carson, 21 December: 3.6 µg/m³, 0.3× usual Carson, 22 December: 3.7 µg/m³, 0.3× usual Carson, 23 December: 10.1 µg/m³, 0.7× usual Carson, 24 December: 18.0 µg/m³, 1.3× usual Carson, 25 December: 37.0 µg/m³, 2.6× usual Carson, 26 December: 28.2 µg/m³, 2.0× usual Carson, 27 December: 25.9 µg/m³, 1.8× usual Carson, 28 December: 23.0 µg/m³, 1.6× usual Carson, 29 December: 23.7 µg/m³, 1.7× usual Carson, 30 December: 6.3 µg/m³, 0.5× usual Carson, 31 December: 13.7 µg/m³, 1.0× usual Carson, 1 January: 26.7 µg/m³, 1.9× usual Jurupa Valley Jurupa Valley, 21 December: 4.1 µg/m³, 0.3× usual Jurupa Valley, 22 December: 8.5 µg/m³, 0.6× usual Jurupa Valley, 23 December: 11.7 µg/m³, 0.8× usual Jurupa Valley, 24 December: 24.5 µg/m³, 1.7× usual Jurupa Valley, 25 December: 33.1 µg/m³, 2.3× usual Jurupa Valley, 26 December: 26.9 µg/m³, 1.9× usual Jurupa Valley, 27 December: 27.3 µg/m³, 1.9× usual Jurupa Valley, 28 December: 45.7 µg/m³, 3.2× usual Jurupa Valley, 29 December: 31.0 µg/m³, 2.2× usual Jurupa Valley, 30 December: 21.4 µg/m³, 1.5× usual Jurupa Valley, 31 December: 13.9 µg/m³, 1.0× usual Jurupa Valley, 1 January: 25.7 µg/m³, 1.8× usual Merced Merced, 21 December: 10.8 µg/m³, 0.8× usual Merced, 22 December: 11.4 µg/m³, 0.9× usual Merced, 23 December: 17.1 µg/m³, 1.3× usual Merced, 24 December: 26.9 µg/m³, 2.0× usual Merced, 25 December: 32.9 µg/m³, 2.5× usual Merced, 26 December: 32.4 µg/m³, 2.5× usual Merced, 27 December: 34.1 µg/m³, 2.6× usual Merced, 28 December: 14.1 µg/m³, 1.1× usual Merced, 29 December: 7.1 µg/m³, 0.5× usual Merced, 30 December: 5.1 µg/m³, 0.4× usual Merced, 31 December: 8.8 µg/m³, 0.7× usual Merced, 1 January: 14.7 µg/m³, 1.1× usual Long Beach Long Beach, 21 December: 3.2 µg/m³, 0.2× usual Long Beach, 22 December: 3.1 µg/m³, 0.2× usual Long Beach, 23 December: 8.9 µg/m³, 0.6× usual Long Beach, 24 December: 13.1 µg/m³, 0.9× usual Long Beach, 25 December: 31.1 µg/m³, 2.2× usual Long Beach, 26 December: 20.2 µg/m³, 1.5× usual Long Beach, 27 December: 20.6 µg/m³, 1.5× usual Long Beach, 28 December: 16.2 µg/m³, 1.2× usual Long Beach, 29 December: 15.5 µg/m³, 1.1× usual Long Beach, 30 December: 4.4 µg/m³, 0.3× usual Long Beach, 31 December: 10.5 µg/m³, 0.8× usual Long Beach, 1 January: 26.5 µg/m³, 1.9× usual Tempe Tempe, 21 December: 4.9 µg/m³, 0.5× usual Tempe, 22 December: 5.5 µg/m³, 0.6× usual Tempe, 23 December: 5.5 µg/m³, 0.6× usual Tempe, 24 December: 20.5 µg/m³, 2.2× usual Tempe, 25 December: 29.9 µg/m³, 3.1× usual Tempe, 26 December: 14.4 µg/m³, 1.5× usual Tempe, 27 December: 15.7 µg/m³, 1.7× usual Tempe, 28 December: 16.1 µg/m³, 1.7× usual Tempe, 29 December: 11.5 µg/m³, 1.2× usual Tempe, 30 December: 6.7 µg/m³, 0.7× usual Tempe, 31 December: 14.1 µg/m³, 1.5× usual Tempe, 1 January: 30.0 µg/m³, 3.2× usual Las Vegas Las Vegas, 21 December: 11.1 µg/m³, 0.9× usual Las Vegas, 22 December: 10.2 µg/m³, 0.8× usual Las Vegas, 23 December: 12.0 µg/m³, 0.9× usual Las Vegas, 24 December: 17.5 µg/m³, 1.4× usual Las Vegas, 25 December: 28.5 µg/m³, 2.2× usual Las Vegas, 26 December: 13.9 µg/m³, 1.1× usual Las Vegas, 27 December: 19.7 µg/m³, 1.5× usual Las Vegas, 28 December: 19.3 µg/m³, 1.5× usual Las Vegas, 29 December: 17.7 µg/m³, 1.4× usual Las Vegas, 30 December: 15.6 µg/m³, 1.2× usual Las Vegas, 31 December: 14.8 µg/m³, 1.1× usual Las Vegas, 1 January: 29.4 µg/m³, 2.3× usual Torrance Torrance, 21 December: 3.5 µg/m³, 0.3× usual Torrance, 22 December: 3.7 µg/m³, 0.3× usual Torrance, 23 December: 10.1 µg/m³, 0.9× usual Torrance, 24 December: 15.5 µg/m³, 1.3× usual Torrance, 25 December: 28.2 µg/m³, 2.4× usual Torrance, 26 December: 24.6 µg/m³, 2.1× usual Torrance, 27 December: 25.0 µg/m³, 2.1× usual Torrance, 28 December: 18.9 µg/m³, 1.6× usual Torrance, 29 December: 20.8 µg/m³, 1.8× usual Torrance, 30 December: 5.9 µg/m³, 0.5× usual Torrance, 31 December: 12.8 µg/m³, 1.1× usual Torrance, 1 January: 24.7 µg/m³, 2.1× usual Modesto Modesto, 21 December: 8.9 µg/m³, 0.7× usual Modesto, 22 December: 10.5 µg/m³, 0.8× usual Modesto, 23 December: 9.6 µg/m³, 0.7× usual Modesto, 24 December: 22.0 µg/m³, 1.7× usual Modesto, 25 December: 27.9 µg/m³, 2.1× usual Modesto, 26 December: 32.8 µg/m³, 2.5× usual Modesto, 27 December: 30.6 µg/m³, 2.3× usual Modesto, 28 December: 14.8 µg/m³, 1.1× usual Modesto, 29 December: 11.7 µg/m³, 0.9× usual Modesto, 30 December: 5.7 µg/m³, 0.4× usual Modesto, 31 December: 13.1 µg/m³, 1.0× usual Modesto, 1 January: 11.4 µg/m³, 0.9× usual Chico Chico, 21 December: 9.3 µg/m³, 1.1× usual Chico, 22 December: 8.1 µg/m³, 1.0× usual Chico, 23 December: 11.3 µg/m³, 1.3× usual Chico, 24 December: 17.4 µg/m³, 2.1× usual Chico, 25 December: 26.8 µg/m³, 3.2× usual Chico, 26 December: 16.1 µg/m³, 1.9× usual Chico, 27 December: 13.8 µg/m³, 1.6× usual Chico, 28 December: 7.2 µg/m³, 0.9× usual Chico, 29 December: 5.5 µg/m³, 0.7× usual Chico, 30 December: 6.7 µg/m³, 0.8× usual Chico, 31 December: 11.1 µg/m³, 1.3× usual Chico, 1 January: 18.8 µg/m³, 2.2× usual Riverside Riverside, 21 December: 2.8 µg/m³, 0.2× usual Riverside, 22 December: 6.2 µg/m³, 0.5× usual Riverside, 23 December: 9.0 µg/m³, 0.8× usual Riverside, 24 December: 19.8 µg/m³, 1.7× usual Riverside, 25 December: 25.6 µg/m³, 2.2× usual Riverside, 26 December: 21.9 µg/m³, 1.9× usual Riverside, 27 December: 21.8 µg/m³, 1.9× usual Riverside, 28 December: 40.6 µg/m³, 3.5× usual Riverside, 29 December: 24.0 µg/m³, 2.1× usual Riverside, 30 December: 19.0 µg/m³, 1.6× usual Riverside, 31 December: 11.7 µg/m³, 1.0× usual Riverside, 1 January: 20.0 µg/m³, 1.7× usual Visalia Visalia, 21 December: 7.8 µg/m³, 0.5× usual Visalia, 22 December: 20.7 µg/m³, 1.3× usual Visalia, 23 December: 19.9 µg/m³, 1.3× usual Visalia, 24 December: 23.6 µg/m³, 1.5× usual Visalia, 25 December: 31.0 µg/m³, 1.9× usual Visalia, 26 December: 42.9 µg/m³, 2.7× usual Visalia, 27 December: 30.3 µg/m³, 1.9× usual Visalia, 28 December: 14.3 µg/m³, 0.9× usual Visalia, 29 December: 8.6 µg/m³, 0.5× usual Visalia, 30 December: 11.5 µg/m³, 0.7× usual Visalia, 31 December: 8.4 µg/m³, 0.5× usual Visalia, 1 January: 26.9 µg/m³, 1.7× usual Bakersfield Bakersfield, 21 December: 5.7 µg/m³, 0.3× usual Bakersfield, 22 December: 12.4 µg/m³, 0.7× usual Bakersfield, 23 December: 21.0 µg/m³, 1.2× usual Bakersfield, 24 December: 23.9 µg/m³, 1.4× usual Bakersfield, 25 December: 30.8 µg/m³, 1.8× usual Bakersfield, 26 December: 38.4 µg/m³, 2.2× usual Bakersfield, 27 December: 37.6 µg/m³, 2.2× usual Bakersfield, 28 December: 31.0 µg/m³, 1.8× usual Bakersfield, 29 December: 12.7 µg/m³, 0.7× usual Bakersfield, 30 December: 7.2 µg/m³, 0.4× usual Bakersfield, 31 December: 19.5 µg/m³, 1.1× usual Bakersfield, 1 January: 29.3 µg/m³, 1.7× usual Hanford Hanford, 21 December: 8.7 µg/m³, 0.5× usual Hanford, 22 December: 19.8 µg/m³, 1.2× usual Hanford, 23 December: 23.4 µg/m³, 1.4× usual Hanford, 24 December: 16.6 µg/m³, 1.0× usual Hanford, 25 December: 27.0 µg/m³, 1.6× usual Hanford, 26 December: 36.5 µg/m³, 2.1× usual Hanford, 27 December: 31.9 µg/m³, 1.9× usual Hanford, 28 December: 26.2 µg/m³, 1.5× usual Hanford, 29 December: 12.7 µg/m³, 0.7× usual Hanford, 30 December: 6.5 µg/m³, 0.4× usual Hanford, 31 December: 9.0 µg/m³, 0.5× usual Hanford, 1 January: 16.1 µg/m³, 0.9× usual Clovis Clovis, 21 December: 7.3 µg/m³, 0.6× usual Clovis, 22 December: 13.9 µg/m³, 1.1× usual Clovis, 23 December: 22.7 µg/m³, 1.7× usual Clovis, 24 December: 24.1 µg/m³, 1.8× usual Clovis, 25 December: 24.0 µg/m³, 1.8× usual Clovis, 26 December: 34.0 µg/m³, 2.6× usual Clovis, 27 December: 22.4 µg/m³, 1.7× usual Clovis, 28 December: 12.2 µg/m³, 0.9× usual Clovis, 29 December: 7.0 µg/m³, 0.5× usual Clovis, 30 December: 6.1 µg/m³, 0.5× usual Clovis, 31 December: 6.5 µg/m³, 0.5× usual Clovis, 1 January: 18.7 µg/m³, 1.4× usual Corcoran Corcoran, 21 December: 5.9 µg/m³, 0.4× usual Corcoran, 22 December: 15.0 µg/m³, 1.0× usual Corcoran, 23 December: 20.3 µg/m³, 1.4× usual Corcoran, 24 December: 16.2 µg/m³, 1.1× usual Corcoran, 25 December: 22.5 µg/m³, 1.6× usual Corcoran, 26 December: 29.3 µg/m³, 2.0× usual Corcoran, 27 December: 21.0 µg/m³, 1.5× usual Corcoran, 28 December: 21.7 µg/m³, 1.5× usual Corcoran, 29 December: 8.6 µg/m³, 0.6× usual Corcoran, 30 December: 5.5 µg/m³, 0.4× usual Corcoran, 31 December: 8.1 µg/m³, 0.6× usual Corcoran, 1 January: 12.9 µg/m³, 0.9× usual Manteca Manteca, 21 December: 8.1 µg/m³, 0.7× usual Manteca, 22 December: 8.1 µg/m³, 0.7× usual Manteca, 23 December: 11.1 µg/m³, 1.0× usual Manteca, 24 December: 16.3 µg/m³, 1.4× usual Manteca, 25 December: 21.5 µg/m³, 1.9× usual Manteca, 26 December: 29.2 µg/m³, 2.6× usual Manteca, 27 December: 20.5 µg/m³, 1.8× usual Manteca, 28 December: 12.4 µg/m³, 1.1× usual Manteca, 29 December: 14.0 µg/m³, 1.2× usual Manteca, 30 December: 3.3 µg/m³, 0.3× usual Manteca, 31 December: 10.8 µg/m³, 0.9× usual Manteca, 1 January: 6.4 µg/m³, 0.6× usual Porterville Porterville, 21 December: 7.1 µg/m³, 0.7× usual Porterville, 22 December: 14.0 µg/m³, 1.3× usual Porterville, 23 December: 17.2 µg/m³, 1.7× usual Porterville, 24 December: 17.7 µg/m³, 1.7× usual Porterville, 25 December: 21.6 µg/m³, 2.1× usual Porterville, 26 December: 27.7 µg/m³, 2.7× usual Porterville, 27 December: 19.7 µg/m³, 1.9× usual Porterville, 28 December: 7.4 µg/m³, 0.7× usual Porterville, 29 December: 8.4 µg/m³, 0.8× usual Porterville, 30 December: 6.8 µg/m³, 0.7× usual Porterville, 31 December: 6.0 µg/m³, 0.6× usual Porterville, 1 January: 15.6 µg/m³, 1.5× usual Lomita Lomita, 21 December: 3.2 µg/m³, 0.4× usual Lomita, 22 December: 3.1 µg/m³, 0.4× usual Lomita, 23 December: 7.3 µg/m³, 0.9× usual Lomita, 24 December: 12.1 µg/m³, 1.4× usual Lomita, 25 December: 16.2 µg/m³, 1.9× usual Lomita, 26 December: 25.7 µg/m³, 3.0× usual Lomita, 27 December: 27.2 µg/m³, 3.2× usual Lomita, 28 December: 18.9 µg/m³, 2.2× usual Lomita, 29 December: 17.9 µg/m³, 2.1× usual Lomita, 30 December: 4.2 µg/m³, 0.5× usual Lomita, 31 December: 7.3 µg/m³, 0.9× usual Lomita, 1 January: 11.5 µg/m³, 1.4× usual San Diego San Diego, 21 December: 5.1 µg/m³, 0.5× usual San Diego, 22 December: 5.2 µg/m³, 0.6× usual San Diego, 23 December: 9.0 µg/m³, 1.0× usual San Diego, 24 December: 13.2 µg/m³, 1.4× usual San Diego, 25 December: 14.7 µg/m³, 1.6× usual San Diego, 26 December: 16.8 µg/m³, 1.8× usual San Diego, 27 December: 26.2 µg/m³, 2.8× usual San Diego, 28 December: 22.9 µg/m³, 2.4× usual San Diego, 29 December: 27.8 µg/m³, 3.0× usual San Diego, 30 December: 14.5 µg/m³, 1.5× usual San Diego, 31 December: 13.3 µg/m³, 1.4× usual San Diego, 1 January: 13.3 µg/m³, 1.4× usual Fontana Fontana, 21 December: 4.5 µg/m³, 0.5× usual Fontana, 22 December: 3.9 µg/m³, 0.4× usual Fontana, 23 December: 6.2 µg/m³, 0.6× usual Fontana, 24 December: 21.7 µg/m³, 2.2× usual Fontana, 25 December: 17.3 µg/m³, 1.7× usual Fontana, 26 December: 17.4 µg/m³, 1.7× usual Fontana, 27 December: 19.7 µg/m³, 2.0× usual Fontana, 28 December: 33.6 µg/m³, 3.4× usual Fontana, 29 December: 28.2 µg/m³, 2.8× usual Fontana, 30 December: 17.7 µg/m³, 1.8× usual Fontana, 31 December: 18.0 µg/m³, 1.8× usual Fontana, 1 January: 17.9 µg/m³, 1.8× usual Anaheim Anaheim, 21 December: 5.0 µg/m³, 0.4× usual Anaheim, 22 December: 5.4 µg/m³, 0.4× usual Anaheim, 23 December: 8.4 µg/m³, 0.7× usual Anaheim, 24 December: 18.4 µg/m³, 1.4× usual Anaheim, 25 December: 21.8 µg/m³, 1.7× usual Anaheim, 26 December: 23.8 µg/m³, 1.9× usual Anaheim, 27 December: 21.7 µg/m³, 1.7× usual Anaheim, 28 December: 31.9 µg/m³, 2.5× usual Anaheim, 29 December: 24.4 µg/m³, 1.9× usual Anaheim, 30 December: 10.9 µg/m³, 0.9× usual Anaheim, 31 December: 13.2 µg/m³, 1.0× usual Anaheim, 1 January: 13.0 µg/m³, 1.0× usual Tijuana Tijuana, 21 December: 14.1 µg/m³, 0.7× usual Tijuana, 22 December: 9.8 µg/m³, 0.5× usual Tijuana, 23 December: 22.2 µg/m³, 1.1× usual Tijuana, 24 December: 28.8 µg/m³, 1.4× usual Tijuana, 25 December: 34.9 µg/m³, 1.7× usual Tijuana, 26 December: 30.8 µg/m³, 1.5× usual Tijuana, 27 December: 37.4 µg/m³, 1.8× usual Tijuana, 28 December: 32.6 µg/m³, 1.6× usual Tijuana, 29 December: 43.5 µg/m³, 2.1× usual Tijuana, 30 December: 24.7 µg/m³, 1.2× usual Tijuana, 31 December: 25.0 µg/m³, 1.2× usual Tijuana, 1 January: 38.8 µg/m³, 1.9× usual 21 Dec 23 25 27 29 31 1 Jan 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
Phoenix Arizona, United States 1 1 January 17.8 5.8× Glendale Arizona, United States 1 1 January 10.6 4.3× Mesa Arizona, United States 1 24 December 9.1 3.5× Riverside California, United States 2 28 December 11.6 3.5× Fontana California, United States 2 28 December 10.0 3.4× Jurupa Valley California, United States 3 28 December 14.1 3.2× Stockton California, United States 3 25 December 12.3 3.2× Arden-Arcade California, United States 3 26 December 9.4 3.2× Lomita California, United States 2 27 December 8.5 3.2× Chico California, United States 1 25 December 8.4 3.2× Tempe Arizona, United States 1 1 January 9.5 3.2× Calexico California, United States 1 24 December 12.5 3.1× Hawthorne California, United States 1 25 December 15.8 3.0× San Diego California, United States 2 29 December 9.4 3.0× Compton California, United States 1 25 December 18.0 2.9× Madera California, United States 3 25 December 13.3 2.8× Turlock California, United States 4 27 December 12.7 2.8× Visalia California, United States 1 26 December 15.9 2.7× Porterville California, United States 1 26 December 10.4 2.7× Carson California, United States 2 25 December 14.0 2.6× Merced California, United States 3 27 December 13.2 2.6× Clovis California, United States 1 26 December 13.2 2.6× Manteca California, United States 1 26 December 11.4 2.6× Anaheim California, United States 1 28 December 12.7 2.5× Modesto California, United States 3 26 December 13.1 2.5× Torrance California, United States 2 25 December 11.8 2.4× Las Vegas Nevada, United States 1 1 January 12.9 2.3× Long Beach California, United States 1 25 December 13.9 2.2× Bakersfield California, United States 2 26 December 17.3 2.2× Hanford California, United States 1 26 December 17.1 2.1× Tijuana Baja California, Mexico 1 29 December 20.5 2.1× Corcoran California, United States 1 26 December 14.4 2.0×
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 and Mexico
Number 11 of 45 episodes in the United States and Mexico 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 Bars: cities reached; colour: the level of the episode's highest daily reading. All 45 .
Use this page SmogRank, Western United States, December 2023: 32 cities with PM2.5 at twice their usual or more, 24 to 29 December 2023, smogrank.com/episodes/2023-12-western-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.
