SmogRank / Episodes / United States
Western United States and Mexico, December 2023
For 5 days, from 24 to 28 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 Tijuana, Baja California, Mexico: 82.9 µg/m³ on 25 December, about 2.5× its usual 33.2.
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 5 24 to 28 December 2023
Worst day 25 December 21 cities counted
Furthest above usual 4.0× Phoenix
Day by day
Play 25 December 21 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 Imperial Beach 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 Hanford Las Vegas Long Beach Bakersfield Torrance Calexico Anaheim Modesto Tijuana Manteca Clovis Merced Carson Porterville Visalia Mesa San Diego Turlock Madera Compton Hawthorne Tempe Chico Lomita Arden-Arcade Stockton Jurupa Valley Fontana Riverside Glendale Phoenix 21 Dec 22 23 24 25 26 27 28 29 30 31 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
Madera Madera, 21 December: 5.8 µg/m³ Madera, 22 December: 12.5 µg/m³ Madera, 23 December: 17.9 µg/m³ Madera, 24 December: 32.1 µg/m³, 2.3× its usual 13.7 Madera, 25 December: 37.3 µg/m³, 2.8× its usual 13.3 Madera, 26 December: 29.6 µg/m³, 2.2× its usual 13.2 Madera, 27 December: 25.0 µg/m³ Madera, 28 December: 12.3 µg/m³ Madera, 29 December: 4.8 µg/m³ Madera, 30 December: 4.1 µg/m³ Madera, 31 December: 7.0 µg/m³ Stockton Stockton, 21 December: 10.1 µg/m³ Stockton, 22 December: 11.4 µg/m³ Stockton, 23 December: 18.5 µg/m³ Stockton, 24 December: 28.8 µg/m³, 2.3× its usual 12.5 Stockton, 25 December: 39.8 µg/m³, 3.2× its usual 12.3 Stockton, 26 December: 37.0 µg/m³, 3.0× its usual 12.5 Stockton, 27 December: 22.9 µg/m³ Stockton, 28 December: 16.8 µg/m³ Stockton, 29 December: 12.6 µg/m³ Stockton, 30 December: 7.1 µg/m³ Stockton, 31 December: 17.5 µg/m³ Arden-Arcade Arden-Arcade, 21 December: 8.9 µg/m³ Arden-Arcade, 22 December: 11.0 µg/m³ Arden-Arcade, 23 December: 20.2 µg/m³ Arden-Arcade, 24 December: 27.8 µg/m³, 2.9× its usual 9.6 Arden-Arcade, 25 December: 28.8 µg/m³, 2.9× its usual 9.8 Arden-Arcade, 26 December: 30.1 µg/m³, 3.2× its usual 9.4 Arden-Arcade, 27 December: 15.6 µg/m³ Arden-Arcade, 28 December: 6.8 µg/m³ Arden-Arcade, 29 December: 7.3 µg/m³ Arden-Arcade, 30 December: 6.4 µg/m³ Arden-Arcade, 31 December: 6.0 µg/m³ Turlock Turlock, 21 December: 11.1 µg/m³ Turlock, 22 December: 13.7 µg/m³ Turlock, 23 December: 10.4 µg/m³ Turlock, 24 December: 26.4 µg/m³, 2.1× its usual 12.7 Turlock, 25 December: 28.4 µg/m³, 2.2× its usual 12.7 Turlock, 26 December: 32.7 µg/m³, 2.6× its usual 12.7 Turlock, 27 December: 35.4 µg/m³, 2.8× its usual 12.7 Turlock, 28 December: 15.1 µg/m³ Turlock, 29 December: 10.0 µg/m³ Turlock, 30 December: 4.7 µg/m³ Turlock, 31 December: 10.8 µg/m³ Tijuana Tijuana, 21 December: 18.3 µg/m³ Tijuana, 22 December: 16.7 µg/m³ Tijuana, 23 December: 32.2 µg/m³ Tijuana, 24 December: 39.1 µg/m³ Tijuana, 25 December: 82.9 µg/m³, 2.5× its usual 33.2 Tijuana, 26 December: 41.7 µg/m³ Tijuana, 27 December: 46.3 µg/m³ Tijuana, 28 December: 40.5 µg/m³ Tijuana, 29 December: 52.6 µg/m³ Tijuana, 30 December: 35.8 µg/m³ Tijuana, 31 December: 36.0 µg/m³ Phoenix Phoenix, 21 December: 7.7 µg/m³ Phoenix, 22 December: 6.7 µg/m³ Phoenix, 23 December: 7.5 µg/m³ Phoenix, 24 December: 34.1 µg/m³ Phoenix, 25 December: 71.0 µg/m³, 4.0× its usual 17.8 Phoenix, 26 December: 29.5 µg/m³ Phoenix, 27 December: 17.5 µg/m³ Phoenix, 28 December: 22.3 µg/m³ Phoenix, 29 December: 19.3 µg/m³ Phoenix, 30 December: 8.2 µg/m³ Phoenix, 31 December: 25.3 µg/m³ Compton Compton, 21 December: 4.6 µg/m³ Compton, 22 December: 6.0 µg/m³ Compton, 23 December: 16.7 µg/m³ Compton, 24 December: 35.0 µg/m³ Compton, 25 December: 51.9 µg/m³, 2.9× its usual 18.0 Compton, 26 December: 25.2 µg/m³ Compton, 27 December: 23.3 µg/m³ Compton, 28 December: 22.1 µg/m³ Compton, 29 December: 24.8 µg/m³ Compton, 30 December: 8.3 µg/m³ Compton, 31 December: 26.0 µg/m³ Hawthorne Hawthorne, 21 December: 3.9 µg/m³ Hawthorne, 22 December: 4.1 µg/m³ Hawthorne, 23 December: 11.8 µg/m³ Hawthorne, 24 December: 24.2 µg/m³ Hawthorne, 25 December: 47.6 µg/m³, 3.0× its usual 15.8 Hawthorne, 26 December: 30.5 µg/m³ Hawthorne, 27 December: 22.0 µg/m³ Hawthorne, 28 December: 22.9 µg/m³ Hawthorne, 29 December: 22.5 µg/m³ Hawthorne, 30 December: 8.1 µg/m³ Hawthorne, 31 December: 16.1 µg/m³ Glendale Glendale, 21 December: 7.6 µg/m³ Glendale, 22 December: 5.6 µg/m³ Glendale, 23 December: 8.0 µg/m³ Glendale, 24 December: 31.9 µg/m³ Glendale, 25 December: 40.9 µg/m³, 3.9× its usual 10.6 Glendale, 26 December: 19.3 µg/m³ Glendale, 27 December: 15.6 µg/m³ Glendale, 28 December: 16.1 µg/m³ Glendale, 29 December: 8.3 µg/m³ Glendale, 30 December: 5.7 µg/m³ Glendale, 31 December: 30.6 µg/m³ Carson Carson, 21 December: 3.6 µg/m³ Carson, 22 December: 3.7 µg/m³ Carson, 23 December: 10.1 µg/m³ Carson, 24 December: 18.0 µg/m³ Carson, 25 December: 37.0 µg/m³, 2.6× its usual 14.0 Carson, 26 December: 28.2 µg/m³, 2.0× its usual 13.9 Carson, 27 December: 25.9 µg/m³ Carson, 28 December: 23.0 µg/m³ Carson, 29 December: 23.7 µg/m³ Carson, 30 December: 6.3 µg/m³ Carson, 31 December: 13.7 µg/m³ Jurupa Valley Jurupa Valley, 21 December: 4.1 µg/m³ Jurupa Valley, 22 December: 8.5 µg/m³ Jurupa Valley, 23 December: 11.7 µg/m³ Jurupa Valley, 24 December: 24.5 µg/m³ Jurupa Valley, 25 December: 33.1 µg/m³, 2.3× its usual 14.3 Jurupa Valley, 26 December: 26.9 µg/m³ Jurupa Valley, 27 December: 27.3 µg/m³ Jurupa Valley, 28 December: 45.7 µg/m³, 3.2× its usual 14.1 Jurupa Valley, 29 December: 31.0 µg/m³ Jurupa Valley, 30 December: 21.4 µg/m³ Jurupa Valley, 31 December: 13.9 µg/m³ Merced Merced, 21 December: 10.8 µg/m³ Merced, 22 December: 11.4 µg/m³ Merced, 23 December: 17.1 µg/m³ Merced, 24 December: 26.9 µg/m³ Merced, 25 December: 32.9 µg/m³, 2.4× its usual 13.7 Merced, 26 December: 32.4 µg/m³, 2.4× its usual 13.6 Merced, 27 December: 34.1 µg/m³, 2.6× its usual 13.2 Merced, 28 December: 14.1 µg/m³ Merced, 29 December: 7.1 µg/m³ Merced, 30 December: 5.1 µg/m³ Merced, 31 December: 8.8 µg/m³ Calexico Calexico, 21 December: no reading Calexico, 22 December: 4.3 µg/m³ Calexico, 23 December: 20.9 µg/m³ Calexico, 24 December: 38.2 µg/m³ Calexico, 25 December: 31.2 µg/m³, 2.5× its usual 12.5 Calexico, 26 December: 20.6 µg/m³ Calexico, 27 December: 23.8 µg/m³ Calexico, 28 December: 20.9 µg/m³ Calexico, 29 December: 10.6 µg/m³ Calexico, 30 December: 15.2 µg/m³ Calexico, 31 December: 13.7 µg/m³ Long Beach Long Beach, 21 December: 3.2 µg/m³ Long Beach, 22 December: 3.1 µg/m³ Long Beach, 23 December: 8.9 µg/m³ Long Beach, 24 December: 13.1 µg/m³ Long Beach, 25 December: 31.1 µg/m³, 2.2× its usual 13.9 Long Beach, 26 December: 20.2 µg/m³ Long Beach, 27 December: 20.6 µg/m³ Long Beach, 28 December: 16.2 µg/m³ Long Beach, 29 December: 15.5 µg/m³ Long Beach, 30 December: 4.4 µg/m³ Long Beach, 31 December: 10.5 µg/m³ Tempe Tempe, 21 December: 4.9 µg/m³ Tempe, 22 December: 5.5 µg/m³ Tempe, 23 December: 5.5 µg/m³ Tempe, 24 December: 20.5 µg/m³ Tempe, 25 December: 29.9 µg/m³, 3.1× its usual 9.5 Tempe, 26 December: 14.4 µg/m³ Tempe, 27 December: 15.7 µg/m³ Tempe, 28 December: 16.1 µg/m³ Tempe, 29 December: 11.5 µg/m³ Tempe, 30 December: 6.7 µg/m³ Tempe, 31 December: 14.1 µg/m³ Las Vegas Las Vegas, 21 December: 11.1 µg/m³ Las Vegas, 22 December: 10.2 µg/m³ Las Vegas, 23 December: 12.0 µg/m³ Las Vegas, 24 December: 17.5 µg/m³ Las Vegas, 25 December: 28.5 µg/m³, 2.2× its usual 12.9 Las Vegas, 26 December: 13.9 µg/m³ Las Vegas, 27 December: 19.7 µg/m³ Las Vegas, 28 December: 19.3 µg/m³ Las Vegas, 29 December: 17.7 µg/m³ Las Vegas, 30 December: 15.6 µg/m³ Las Vegas, 31 December: 14.8 µg/m³ Torrance Torrance, 21 December: 3.5 µg/m³ Torrance, 22 December: 3.7 µg/m³ Torrance, 23 December: 10.1 µg/m³ Torrance, 24 December: 15.5 µg/m³ Torrance, 25 December: 28.2 µg/m³, 2.4× its usual 11.8 Torrance, 26 December: 24.6 µg/m³ Torrance, 27 December: 25.0 µg/m³, 2.1× its usual 11.8 Torrance, 28 December: 18.9 µg/m³ Torrance, 29 December: 20.8 µg/m³ Torrance, 30 December: 5.9 µg/m³ Torrance, 31 December: 12.8 µg/m³ Modesto Modesto, 21 December: 8.9 µg/m³ Modesto, 22 December: 10.5 µg/m³ Modesto, 23 December: 9.6 µg/m³ Modesto, 24 December: 22.0 µg/m³ Modesto, 25 December: 27.9 µg/m³, 2.1× its usual 13.0 Modesto, 26 December: 32.8 µg/m³, 2.5× its usual 13.1 Modesto, 27 December: 30.6 µg/m³, 2.4× its usual 12.7 Modesto, 28 December: 14.8 µg/m³ Modesto, 29 December: 11.7 µg/m³ Modesto, 30 December: 5.7 µg/m³ Modesto, 31 December: 13.1 µg/m³ Chico Chico, 21 December: 9.3 µg/m³ Chico, 22 December: 8.1 µg/m³ Chico, 23 December: 11.3 µg/m³ Chico, 24 December: 17.4 µg/m³ Chico, 25 December: 26.8 µg/m³, 3.2× its usual 8.4 Chico, 26 December: 16.1 µg/m³ Chico, 27 December: 13.8 µg/m³ Chico, 28 December: 7.2 µg/m³ Chico, 29 December: 5.5 µg/m³ Chico, 30 December: 6.7 µg/m³ Chico, 31 December: 11.1 µg/m³ Riverside Riverside, 21 December: 2.8 µg/m³ Riverside, 22 December: 6.2 µg/m³ Riverside, 23 December: 9.0 µg/m³ Riverside, 24 December: 19.8 µg/m³ Riverside, 25 December: 25.6 µg/m³, 2.2× its usual 11.4 Riverside, 26 December: 21.9 µg/m³ Riverside, 27 December: 21.8 µg/m³ Riverside, 28 December: 40.6 µg/m³, 3.5× its usual 11.6 Riverside, 29 December: 24.0 µg/m³ Riverside, 30 December: 19.0 µg/m³ Riverside, 31 December: 11.7 µg/m³ Mesa Mesa, 21 December: 6.7 µg/m³ Mesa, 22 December: 5.1 µg/m³ Mesa, 23 December: 6.7 µg/m³ Mesa, 24 December: 32.1 µg/m³ Mesa, 25 December: 25.5 µg/m³, 2.8× its usual 9.1 Mesa, 26 December: 15.5 µg/m³ Mesa, 27 December: 11.0 µg/m³ Mesa, 28 December: 14.7 µg/m³ Mesa, 29 December: 9.6 µg/m³ Mesa, 30 December: 5.0 µg/m³ Mesa, 31 December: 16.9 µg/m³ Visalia Visalia, 21 December: 7.8 µg/m³ Visalia, 22 December: 20.7 µg/m³ Visalia, 23 December: 19.9 µg/m³ Visalia, 24 December: 23.6 µg/m³ Visalia, 25 December: 31.0 µg/m³ Visalia, 26 December: 42.9 µg/m³, 2.7× its usual 15.9 Visalia, 27 December: 30.3 µg/m³ Visalia, 28 December: 14.3 µg/m³ Visalia, 29 December: 8.6 µg/m³ Visalia, 30 December: 11.5 µg/m³ Visalia, 31 December: 8.4 µg/m³ Bakersfield Bakersfield, 21 December: 5.7 µg/m³ Bakersfield, 22 December: 12.4 µg/m³ Bakersfield, 23 December: 21.0 µg/m³ Bakersfield, 24 December: 23.9 µg/m³ Bakersfield, 25 December: 30.8 µg/m³ Bakersfield, 26 December: 38.4 µg/m³, 2.2× its usual 17.3 Bakersfield, 27 December: 37.6 µg/m³, 2.2× its usual 17.4 Bakersfield, 28 December: 31.0 µg/m³ Bakersfield, 29 December: 12.7 µg/m³ Bakersfield, 30 December: 7.2 µg/m³ Bakersfield, 31 December: 19.5 µg/m³ Hanford Hanford, 21 December: 8.7 µg/m³ Hanford, 22 December: 19.8 µg/m³ Hanford, 23 December: 23.4 µg/m³ Hanford, 24 December: 16.6 µg/m³ Hanford, 25 December: 27.0 µg/m³ Hanford, 26 December: 36.5 µg/m³, 2.1× its usual 17.1 Hanford, 27 December: 31.9 µg/m³ Hanford, 28 December: 26.2 µg/m³ Hanford, 29 December: 12.7 µg/m³ Hanford, 30 December: 6.5 µg/m³ Hanford, 31 December: 9.0 µg/m³ Clovis Clovis, 21 December: 7.3 µg/m³ Clovis, 22 December: 13.9 µg/m³ Clovis, 23 December: 22.7 µg/m³ Clovis, 24 December: 24.1 µg/m³ Clovis, 25 December: 24.0 µg/m³ Clovis, 26 December: 34.0 µg/m³, 2.6× its usual 13.2 Clovis, 27 December: 22.4 µg/m³ Clovis, 28 December: 12.2 µg/m³ Clovis, 29 December: 7.0 µg/m³ Clovis, 30 December: 6.1 µg/m³ Clovis, 31 December: 6.5 µg/m³ Corcoran Corcoran, 21 December: 5.9 µg/m³ Corcoran, 22 December: 15.0 µg/m³ Corcoran, 23 December: 20.3 µg/m³ Corcoran, 24 December: 16.2 µg/m³ Corcoran, 25 December: 22.5 µg/m³ Corcoran, 26 December: 29.3 µg/m³, 2.0× its usual 14.4 Corcoran, 27 December: 21.0 µg/m³ Corcoran, 28 December: 21.7 µg/m³ Corcoran, 29 December: 8.6 µg/m³ Corcoran, 30 December: 5.5 µg/m³ Corcoran, 31 December: 8.1 µg/m³ Manteca Manteca, 21 December: 8.1 µg/m³ Manteca, 22 December: 8.1 µg/m³ Manteca, 23 December: 11.1 µg/m³ Manteca, 24 December: 16.3 µg/m³ Manteca, 25 December: 21.5 µg/m³ Manteca, 26 December: 29.2 µg/m³, 2.6× its usual 11.4 Manteca, 27 December: 20.5 µg/m³ Manteca, 28 December: 12.4 µg/m³ Manteca, 29 December: 14.0 µg/m³ Manteca, 30 December: 3.3 µg/m³ Manteca, 31 December: 10.8 µg/m³ Porterville Porterville, 21 December: 7.1 µg/m³ Porterville, 22 December: 14.0 µg/m³ Porterville, 23 December: 17.2 µg/m³ Porterville, 24 December: 17.7 µg/m³ Porterville, 25 December: 21.6 µg/m³ Porterville, 26 December: 27.7 µg/m³, 2.7× its usual 10.4 Porterville, 27 December: 19.7 µg/m³ Porterville, 28 December: 7.4 µg/m³ Porterville, 29 December: 8.4 µg/m³ Porterville, 30 December: 6.8 µg/m³ Porterville, 31 December: 6.0 µg/m³ Lomita Lomita, 21 December: 3.2 µg/m³ Lomita, 22 December: 3.1 µg/m³ Lomita, 23 December: 7.3 µg/m³ Lomita, 24 December: 12.1 µg/m³ Lomita, 25 December: 16.2 µg/m³ Lomita, 26 December: 25.7 µg/m³, 3.1× its usual 8.4 Lomita, 27 December: 27.2 µg/m³, 3.2× its usual 8.5 Lomita, 28 December: 18.9 µg/m³ Lomita, 29 December: 17.9 µg/m³ Lomita, 30 December: 4.2 µg/m³ Lomita, 31 December: 7.3 µg/m³ San Diego San Diego, 21 December: 5.1 µg/m³ San Diego, 22 December: 5.2 µg/m³ San Diego, 23 December: 9.0 µg/m³ San Diego, 24 December: 13.2 µg/m³ San Diego, 25 December: 14.7 µg/m³ San Diego, 26 December: 16.8 µg/m³ San Diego, 27 December: 26.2 µg/m³, 2.8× its usual 9.5 San Diego, 28 December: 22.9 µg/m³ San Diego, 29 December: 27.8 µg/m³ San Diego, 30 December: 14.5 µg/m³ San Diego, 31 December: 13.3 µg/m³ Fontana Fontana, 21 December: 4.5 µg/m³ Fontana, 22 December: 3.9 µg/m³ Fontana, 23 December: 6.2 µg/m³ Fontana, 24 December: 21.7 µg/m³ Fontana, 25 December: 17.3 µg/m³ Fontana, 26 December: 17.4 µg/m³ Fontana, 27 December: 19.7 µg/m³ Fontana, 28 December: 33.6 µg/m³, 3.4× its usual 10.0 Fontana, 29 December: 28.2 µg/m³ Fontana, 30 December: 17.7 µg/m³ Fontana, 31 December: 18.0 µg/m³ Anaheim Anaheim, 21 December: 5.0 µg/m³ Anaheim, 22 December: 5.4 µg/m³ Anaheim, 23 December: 8.4 µg/m³ Anaheim, 24 December: 18.4 µg/m³ Anaheim, 25 December: 21.8 µg/m³ Anaheim, 26 December: 23.8 µg/m³ Anaheim, 27 December: 21.7 µg/m³ Anaheim, 28 December: 31.9 µg/m³, 2.5× its usual 12.7 Anaheim, 29 December: 24.4 µg/m³ Anaheim, 30 December: 10.9 µg/m³ Anaheim, 31 December: 13.2 µg/m³ 21 Dec 23 25 27 29 31 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 25 December 17.8 4.0× Glendale Arizona, United States 1 25 December 10.6 3.9× Riverside California, United States 2 28 December 11.6 3.5× Fontana California, United States 1 28 December 10.0 3.4× Jurupa Valley California, United States 2 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 25 December 9.5 3.1× Hawthorne California, United States 1 25 December 15.8 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× San Diego California, United States 1 27 December 9.5 2.8× Mesa Arizona, United States 1 25 December 9.1 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× Tijuana Baja California, Mexico 1 25 December 33.2 2.5× Modesto California, United States 3 26 December 13.1 2.5× Anaheim California, United States 1 28 December 12.7 2.5× Calexico California, United States 1 25 December 12.5 2.5× Torrance California, United States 2 25 December 11.8 2.4× Bakersfield California, United States 2 26 December 17.3 2.2× Long Beach California, United States 1 25 December 13.9 2.2× Las Vegas Nevada, United States 1 25 December 12.9 2.2× Hanford California, United States 1 26 December 17.1 2.1× Corcoran California, United States 1 26 December 14.4 2.0×
Daily means in µg/m³, over the days each city counted in this episode. Highest: its highest of those days. Usual: the city's median for the time of year of that day (its days within 21 days of the date, every year, leaving out the week around it). Above usual: its highest day against that, with a usual under 5 µg/m³ taken as 5.
Against other episodes in the United States and Mexico
Number 30 of 141 episodes in the United States and Mexico since our records began, by cities reached.
Eastern United States and Canada, 25 June to 2 July 2023 280 North-eastern United States and Canada, July 2026 264 Eastern United States and Canada, May and June 2023 261 North-eastern United States and Canada, 30 July to 9 August 2025 241 Eastern United States and Canada, July 2023 240 North-eastern United States and Canada, 3 to 9 June 2025 196 Eastern United States and Canada, 14 to 19 June 2023 161 North-eastern United States and Canada, 12 to 16 July 2025 119 North-western United States and Canada, August 2023 110 North-eastern United States and Canada, 10 to 14 June 2025 104 North-western United States and Canada, 4 to 11 August 2026 99 North-eastern United States and Canada, 14 to 19 February 2026 96 Western United States and Mexico, December 2023 32 Bars: cities reached; colour: the level of the episode's highest daily reading. All 141 .
Use this page SmogRank, Western United States and Mexico, December 2023: 32 cities with PM2.5 at twice their usual or more, 24 to 28 December 2023, smogrank.com/episodes/2023-12-western-united-states-and-mexico (accessed 4 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.
