SmogRank / Episodes / United States
Western United States, December 2024
For 5 days, from 20 to 24 December 2024, 25 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: 56.2 µg/m³ on 21 December, about 2.2× its usual 25.2.
No cause named We have no fire or smoke records for these days, so we only say what the measurements show.
Cities reached 25 in 2 countries
Days 5 20 to 24 December 2024
Worst day 23 December 12 cities counted
Furthest above usual 5.8× Glendora
Day by day
Play 23 December 12 cities at twice their usual or more
Fillmore Santa Clarita Lancaster Simi Valley Thousand Oaks Oxnard La Crescenta-Montrose Santa Barbara Corcoran Goleta Ridgecrest Visalia Carson Lomita Long Beach Orcutt Victorville Nipomo Lompoc Arroyo Grande San Luis Obispo Fresno Atascadero Clovis Madera Banning Temecula Oceanside Merced Poway San Diego Indio El Cajon Chula Vista Imperial Beach Hollister Salinas Prunedale Gilroy Seaside Watsonville Summerlin South Live Oak Enterprise Santa Cruz Spring Valley Stockton San Jose Las Vegas Livermore Henderson Brawley Pleasanton El Centro Boulder City Redwood City San Leandro Concord Oakland South San Francisco Martinez Berkeley San Francisco Richmond Vallejo San Rafael Yuma Mesquite Hawthorne Anaheim Bakersfield Compton Calexico Torrance Hanford Tijuana Porterville Modesto Manteca Inglewood Turlock Los Angeles Santa Monica Riverside Sunnyvale Jurupa Valley Fontana Burbank Palo Alto Agoura Tracy Lake Elsinore Glendora 17 Dec 18 19 20 21 22 23 24 25 26 27 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, 17 December: 26.1 µg/m³, 2.0× usual Calexico, 18 December: 8.4 µg/m³, 0.6× usual Calexico, 19 December: 13.6 µg/m³, 1.0× usual Calexico, 20 December: 19.1 µg/m³, 1.5× usual Calexico, 21 December: no reading Calexico, 22 December: no reading Calexico, 23 December: 13.3 µg/m³, 1.0× usual Calexico, 24 December: 26.9 µg/m³, 2.1× usual Calexico, 25 December: 12.0 µg/m³, 0.9× usual Calexico, 26 December: 14.9 µg/m³, 1.1× usual Calexico, 27 December: no reading Tijuana Tijuana, 17 December: no reading Tijuana, 18 December: no reading Tijuana, 19 December: no reading Tijuana, 20 December: 52.3 µg/m³, 2.1× usual Tijuana, 21 December: 56.2 µg/m³, 2.2× usual Tijuana, 22 December: 37.4 µg/m³, 1.5× usual Tijuana, 23 December: 38.8 µg/m³, 1.5× usual Tijuana, 24 December: 22.9 µg/m³, 0.9× usual Tijuana, 25 December: 31.1 µg/m³, 1.2× usual Tijuana, 26 December: 35.9 µg/m³, 1.4× usual Tijuana, 27 December: 33.4 µg/m³, 1.3× usual Bakersfield Bakersfield, 17 December: 15.7 µg/m³, 0.8× usual Bakersfield, 18 December: 13.9 µg/m³, 0.7× usual Bakersfield, 19 December: 29.6 µg/m³, 1.5× usual Bakersfield, 20 December: 39.8 µg/m³, 2.0× usual Bakersfield, 21 December: 38.5 µg/m³, 1.9× usual Bakersfield, 22 December: 33.3 µg/m³, 1.7× usual Bakersfield, 23 December: 31.3 µg/m³, 1.6× usual Bakersfield, 24 December: 11.2 µg/m³, 0.6× usual Bakersfield, 25 December: 8.6 µg/m³, 0.4× usual Bakersfield, 26 December: 11.2 µg/m³, 0.6× usual Bakersfield, 27 December: 6.2 µg/m³, 0.3× usual Turlock Turlock, 17 December: 8.4 µg/m³, 0.6× usual Turlock, 18 December: 16.0 µg/m³, 1.2× usual Turlock, 19 December: 18.1 µg/m³, 1.3× usual Turlock, 20 December: 37.6 µg/m³, 2.7× usual Turlock, 21 December: 26.1 µg/m³, 1.9× usual Turlock, 22 December: 17.4 µg/m³, 1.3× usual Turlock, 23 December: 26.5 µg/m³, 1.9× usual Turlock, 24 December: 9.9 µg/m³, 0.7× usual Turlock, 25 December: 7.8 µg/m³, 0.6× usual Turlock, 26 December: 10.2 µg/m³, 0.7× usual Turlock, 27 December: 10.1 µg/m³, 0.7× usual Palo Alto Palo Alto, 17 December: 15.4 µg/m³, 1.7× usual Palo Alto, 18 December: 15.3 µg/m³, 1.7× usual Palo Alto, 19 December: 24.3 µg/m³, 2.7× usual Palo Alto, 20 December: 36.1 µg/m³, 4.1× usual Palo Alto, 21 December: 12.4 µg/m³, 1.4× usual Palo Alto, 22 December: 20.8 µg/m³, 2.3× usual Palo Alto, 23 December: 15.3 µg/m³, 1.7× usual Palo Alto, 24 December: 2.1 µg/m³, 0.2× usual Palo Alto, 25 December: 3.8 µg/m³, 0.4× usual Palo Alto, 26 December: 2.6 µg/m³, 0.3× usual Palo Alto, 27 December: 4.1 µg/m³, 0.5× usual Modesto Modesto, 17 December: 6.5 µg/m³, 0.5× usual Modesto, 18 December: 14.6 µg/m³, 1.0× usual Modesto, 19 December: 16.8 µg/m³, 1.2× usual Modesto, 20 December: 35.2 µg/m³, 2.5× usual Modesto, 21 December: no reading Modesto, 22 December: no reading Modesto, 23 December: 25.8 µg/m³, 1.8× usual Modesto, 24 December: 9.7 µg/m³, 0.7× usual Modesto, 25 December: 8.6 µg/m³, 0.6× usual Modesto, 26 December: 9.4 µg/m³, 0.7× usual Modesto, 27 December: 11.1 µg/m³, 0.8× usual Manteca Manteca, 17 December: 8.7 µg/m³, 0.7× usual Manteca, 18 December: 12.5 µg/m³, 1.0× usual Manteca, 19 December: 17.2 µg/m³, 1.4× usual Manteca, 20 December: 29.7 µg/m³, 2.5× usual Manteca, 21 December: 27.0 µg/m³, 2.2× usual Manteca, 22 December: 14.6 µg/m³, 1.2× usual Manteca, 23 December: 22.1 µg/m³, 1.8× usual Manteca, 24 December: 8.5 µg/m³, 0.7× usual Manteca, 25 December: 7.6 µg/m³, 0.6× usual Manteca, 26 December: 8.9 µg/m³, 0.7× usual Manteca, 27 December: 10.1 µg/m³, 0.8× usual Los Angeles Los Angeles, 17 December: 17.4 µg/m³, 1.4× usual Los Angeles, 18 December: 11.3 µg/m³, 0.9× usual Los Angeles, 19 December: 14.8 µg/m³, 1.2× usual Los Angeles, 20 December: 29.6 µg/m³, 2.4× usual Los Angeles, 21 December: 25.6 µg/m³, 2.1× usual Los Angeles, 22 December: 31.4 µg/m³, 2.6× usual Los Angeles, 23 December: 38.0 µg/m³, 3.1× usual Los Angeles, 24 December: 29.0 µg/m³, 2.4× usual Los Angeles, 25 December: 12.0 µg/m³, 1.0× usual Los Angeles, 26 December: 14.7 µg/m³, 1.2× usual Los Angeles, 27 December: 12.4 µg/m³, 1.0× usual Burbank Burbank, 17 December: 17.2 µg/m³, 1.6× usual Burbank, 18 December: 10.5 µg/m³, 1.0× usual Burbank, 19 December: 14.2 µg/m³, 1.3× usual Burbank, 20 December: 28.0 µg/m³, 2.6× usual Burbank, 21 December: 27.2 µg/m³, 2.5× usual Burbank, 22 December: 33.5 µg/m³, 3.1× usual Burbank, 23 December: 42.9 µg/m³, 4.0× usual Burbank, 24 December: 31.1 µg/m³, 2.9× usual Burbank, 25 December: 9.5 µg/m³, 0.9× usual Burbank, 26 December: 14.9 µg/m³, 1.4× usual Burbank, 27 December: 14.7 µg/m³, 1.4× usual Sunnyvale Sunnyvale, 17 December: 7.7 µg/m³, 1.1× usual Sunnyvale, 18 December: 6.7 µg/m³, 0.9× usual Sunnyvale, 19 December: 12.8 µg/m³, 1.8× usual Sunnyvale, 20 December: 25.7 µg/m³, 3.5× usual Sunnyvale, 21 December: 8.6 µg/m³, 1.2× usual Sunnyvale, 22 December: 13.4 µg/m³, 1.8× usual Sunnyvale, 23 December: 9.6 µg/m³, 1.3× usual Sunnyvale, 24 December: 2.5 µg/m³, 0.3× usual Sunnyvale, 25 December: 3.3 µg/m³, 0.5× usual Sunnyvale, 26 December: 2.8 µg/m³, 0.4× usual Sunnyvale, 27 December: 4.0 µg/m³, 0.5× usual Tracy Tracy, 17 December: 5.3 µg/m³, 0.9× usual Tracy, 18 December: 8.2 µg/m³, 1.5× usual Tracy, 19 December: 13.5 µg/m³, 2.4× usual Tracy, 20 December: 25.1 µg/m³, 4.5× usual Tracy, 21 December: 16.1 µg/m³, 2.9× usual Tracy, 22 December: 11.5 µg/m³, 2.1× usual Tracy, 23 December: 12.3 µg/m³, 2.2× usual Tracy, 24 December: 5.7 µg/m³, 1.0× usual Tracy, 25 December: 4.3 µg/m³, 0.8× usual Tracy, 26 December: 7.5 µg/m³, 1.3× usual Tracy, 27 December: 7.5 µg/m³, 1.3× usual Jurupa Valley Jurupa Valley, 17 December: 15.3 µg/m³, 1.1× usual Jurupa Valley, 18 December: 2.6 µg/m³, 0.2× usual Jurupa Valley, 19 December: 13.9 µg/m³, 1.0× usual Jurupa Valley, 20 December: 22.6 µg/m³, 1.6× usual Jurupa Valley, 21 December: 41.8 µg/m³, 2.9× usual Jurupa Valley, 22 December: 51.9 µg/m³, 3.6× usual Jurupa Valley, 23 December: 36.3 µg/m³, 2.5× usual Jurupa Valley, 24 December: 25.6 µg/m³, 1.8× usual Jurupa Valley, 25 December: 27.6 µg/m³, 1.9× usual Jurupa Valley, 26 December: 19.4 µg/m³, 1.4× usual Jurupa Valley, 27 December: 22.0 µg/m³, 1.5× usual Riverside Riverside, 17 December: 12.7 µg/m³, 1.1× usual Riverside, 18 December: 3.7 µg/m³, 0.3× usual Riverside, 19 December: 9.6 µg/m³, 0.8× usual Riverside, 20 December: 18.3 µg/m³, 1.5× usual Riverside, 21 December: 35.3 µg/m³, 2.9× usual Riverside, 22 December: 41.6 µg/m³, 3.5× usual Riverside, 23 December: 32.8 µg/m³, 2.7× usual Riverside, 24 December: 22.2 µg/m³, 1.8× usual Riverside, 25 December: 20.0 µg/m³, 1.7× usual Riverside, 26 December: 14.3 µg/m³, 1.2× usual Riverside, 27 December: 19.4 µg/m³, 1.6× usual Fontana Fontana, 17 December: 9.4 µg/m³, 0.9× usual Fontana, 18 December: 5.2 µg/m³, 0.5× usual Fontana, 19 December: 13.1 µg/m³, 1.3× usual Fontana, 20 December: 20.7 µg/m³, 2.0× usual Fontana, 21 December: 31.8 µg/m³, 3.1× usual Fontana, 22 December: 39.6 µg/m³, 3.9× usual Fontana, 23 December: 36.3 µg/m³, 3.6× usual Fontana, 24 December: 24.8 µg/m³, 2.4× usual Fontana, 25 December: 15.0 µg/m³, 1.5× usual Fontana, 26 December: 12.2 µg/m³, 1.2× usual Fontana, 27 December: 15.6 µg/m³, 1.5× usual Anaheim Anaheim, 17 December: 16.1 µg/m³, 1.2× usual Anaheim, 18 December: 11.0 µg/m³, 0.8× usual Anaheim, 19 December: 14.3 µg/m³, 1.1× usual Anaheim, 20 December: 23.7 µg/m³, 1.8× usual Anaheim, 21 December: 26.5 µg/m³, 2.0× usual Anaheim, 22 December: 23.7 µg/m³, 1.8× usual Anaheim, 23 December: 16.9 µg/m³, 1.3× usual Anaheim, 24 December: 18.6 µg/m³, 1.4× usual Anaheim, 25 December: 11.3 µg/m³, 0.9× usual Anaheim, 26 December: 13.7 µg/m³, 1.1× usual Anaheim, 27 December: 11.4 µg/m³, 0.9× usual Glendora Glendora, 17 December: 6.3 µg/m³, 1.1× usual Glendora, 18 December: 1.9 µg/m³, 0.3× usual Glendora, 19 December: 3.3 µg/m³, 0.6× usual Glendora, 20 December: 13.5 µg/m³, 2.3× usual Glendora, 21 December: 22.5 µg/m³, 3.8× usual Glendora, 22 December: 34.4 µg/m³, 5.8× usual Glendora, 23 December: 24.0 µg/m³, 4.1× usual Glendora, 24 December: 20.8 µg/m³, 3.5× usual Glendora, 25 December: 7.2 µg/m³, 1.2× usual Glendora, 26 December: 5.6 µg/m³, 0.9× usual Glendora, 27 December: 8.4 µg/m³, 1.4× usual Lake Elsinore Lake Elsinore, 17 December: 9.0 µg/m³, 1.5× usual Lake Elsinore, 18 December: 4.5 µg/m³, 0.8× usual Lake Elsinore, 19 December: 4.7 µg/m³, 0.8× usual Lake Elsinore, 20 December: 8.7 µg/m³, 1.5× usual Lake Elsinore, 21 December: 21.0 µg/m³, 3.6× usual Lake Elsinore, 22 December: 30.9 µg/m³, 5.2× usual Lake Elsinore, 23 December: 16.3 µg/m³, 2.8× usual Lake Elsinore, 24 December: 15.2 µg/m³, 2.6× usual Lake Elsinore, 25 December: 6.8 µg/m³, 1.2× usual Lake Elsinore, 26 December: 11.5 µg/m³, 1.9× usual Lake Elsinore, 27 December: 11.1 µg/m³, 1.9× usual Porterville Porterville, 17 December: 12.9 µg/m³, 1.2× usual Porterville, 18 December: 18.7 µg/m³, 1.7× usual Porterville, 19 December: 21.2 µg/m³, 1.9× usual Porterville, 20 December: 19.5 µg/m³, 1.7× usual Porterville, 21 December: 14.5 µg/m³, 1.3× usual Porterville, 22 December: 27.5 µg/m³, 2.5× usual Porterville, 23 December: 15.0 µg/m³, 1.3× usual Porterville, 24 December: 5.8 µg/m³, 0.5× usual Porterville, 25 December: 11.0 µg/m³, 1.0× usual Porterville, 26 December: 7.5 µg/m³, 0.7× usual Porterville, 27 December: 7.3 µg/m³, 0.7× usual Hanford Hanford, 17 December: 8.6 µg/m³, 0.5× usual Hanford, 18 December: 18.2 µg/m³, 1.1× usual Hanford, 19 December: 29.9 µg/m³, 1.7× usual Hanford, 20 December: 13.2 µg/m³, 0.8× usual Hanford, 21 December: 17.1 µg/m³, 1.0× usual Hanford, 22 December: 33.1 µg/m³, 1.9× usual Hanford, 23 December: 36.7 µg/m³, 2.1× usual Hanford, 24 December: 11.6 µg/m³, 0.7× usual Hanford, 25 December: 8.4 µg/m³, 0.5× usual Hanford, 26 December: 13.7 µg/m³, 0.8× usual Hanford, 27 December: 12.7 µg/m³, 0.7× usual Hawthorne Hawthorne, 17 December: 16.4 µg/m³, 1.1× usual Hawthorne, 18 December: 16.9 µg/m³, 1.2× usual Hawthorne, 19 December: 16.7 µg/m³, 1.2× usual Hawthorne, 20 December: 24.7 µg/m³, 1.7× usual Hawthorne, 21 December: 18.0 µg/m³, 1.3× usual Hawthorne, 22 December: 20.8 µg/m³, 1.4× usual Hawthorne, 23 December: 28.9 µg/m³, 2.0× usual Hawthorne, 24 December: 21.7 µg/m³, 1.5× usual Hawthorne, 25 December: 10.8 µg/m³, 0.8× usual Hawthorne, 26 December: 18.7 µg/m³, 1.3× usual Hawthorne, 27 December: 16.5 µg/m³, 1.1× usual Inglewood Inglewood, 17 December: 15.0 µg/m³, 1.4× usual Inglewood, 18 December: 10.7 µg/m³, 1.0× usual Inglewood, 19 December: 19.0 µg/m³, 1.8× usual Inglewood, 20 December: 23.8 µg/m³, 2.3× usual Inglewood, 21 December: 17.9 µg/m³, 1.7× usual Inglewood, 22 December: 19.1 µg/m³, 1.8× usual Inglewood, 23 December: 28.5 µg/m³, 2.7× usual Inglewood, 24 December: 21.2 µg/m³, 2.0× usual Inglewood, 25 December: 8.1 µg/m³, 0.8× usual Inglewood, 26 December: 16.2 µg/m³, 1.6× usual Inglewood, 27 December: 14.4 µg/m³, 1.4× usual Santa Monica Santa Monica, 17 December: 10.1 µg/m³, 1.2× usual Santa Monica, 18 December: 4.8 µg/m³, 0.6× usual Santa Monica, 19 December: 11.0 µg/m³, 1.3× usual Santa Monica, 20 December: 19.4 µg/m³, 2.4× usual Santa Monica, 21 December: 16.8 µg/m³, 2.0× usual Santa Monica, 22 December: 17.2 µg/m³, 2.1× usual Santa Monica, 23 December: 28.4 µg/m³, 3.5× usual Santa Monica, 24 December: 17.2 µg/m³, 2.1× usual Santa Monica, 25 December: 5.2 µg/m³, 0.6× usual Santa Monica, 26 December: 10.3 µg/m³, 1.3× usual Santa Monica, 27 December: 15.3 µg/m³, 1.9× usual Agoura Agoura, 17 December: 5.4 µg/m³, 0.9× usual Agoura, 18 December: 4.5 µg/m³, 0.8× usual Agoura, 19 December: 5.4 µg/m³, 0.9× usual Agoura, 20 December: 12.4 µg/m³, 2.1× usual Agoura, 21 December: 11.6 µg/m³, 2.0× usual Agoura, 22 December: 9.8 µg/m³, 1.7× usual Agoura, 23 December: 26.8 µg/m³, 4.5× usual Agoura, 24 December: 19.7 µg/m³, 3.3× usual Agoura, 25 December: 5.2 µg/m³, 0.9× usual Agoura, 26 December: 8.1 µg/m³, 1.4× usual Agoura, 27 December: 14.9 µg/m³, 2.5× usual Torrance Torrance, 17 December: 11.8 µg/m³, 1.0× usual Torrance, 18 December: 10.6 µg/m³, 0.9× usual Torrance, 19 December: 13.8 µg/m³, 1.2× usual Torrance, 20 December: 23.4 µg/m³, 2.0× usual Torrance, 21 December: 13.0 µg/m³, 1.1× usual Torrance, 22 December: 14.4 µg/m³, 1.2× usual Torrance, 23 December: 25.1 µg/m³, 2.1× usual Torrance, 24 December: 20.6 µg/m³, 1.7× usual Torrance, 25 December: 8.6 µg/m³, 0.7× usual Torrance, 26 December: 13.0 µg/m³, 1.1× usual Torrance, 27 December: 12.2 µg/m³, 1.0× usual Compton Compton, 17 December: 20.2 µg/m³, 1.1× usual Compton, 18 December: 19.3 µg/m³, 1.1× usual Compton, 19 December: 14.4 µg/m³, 0.8× usual Compton, 20 December: 21.6 µg/m³, 1.2× usual Compton, 21 December: 16.5 µg/m³, 0.9× usual Compton, 22 December: 26.9 µg/m³, 1.5× usual Compton, 23 December: 32.2 µg/m³, 1.8× usual Compton, 24 December: 37.7 µg/m³, 2.1× usual Compton, 25 December: 24.4 µg/m³, 1.4× usual Compton, 26 December: 20.5 µg/m³, 1.2× usual Compton, 27 December: 8.4 µg/m³, 0.5× usual 17 Dec 19 21 23 25 27 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
Glendora California, United States 1 22 December 5.9 5.8× Lake Elsinore California, United States 1 22 December 5.9 5.2× Agoura California, United States 1 23 December 5.9 4.5× Tracy California, United States 1 20 December 5.6 4.5× Palo Alto California, United States 1 20 December 8.9 4.1× Burbank California, United States 5 23 December 10.8 4.0× Fontana California, United States 3 22 December 10.2 3.9× Jurupa Valley California, United States 3 22 December 14.3 3.6× Sunnyvale California, United States 1 20 December 7.3 3.5× Riverside California, United States 3 22 December 12.0 3.5× Santa Monica California, United States 1 23 December 8.2 3.5× Los Angeles California, United States 5 23 December 12.3 3.1× Inglewood California, United States 1 23 December 10.4 2.7× Turlock California, United States 2 20 December 13.9 2.7× Modesto California, United States 1 20 December 14.2 2.5× Porterville California, United States 1 22 December 11.2 2.5× Manteca California, United States 1 20 December 12.1 2.5× Tijuana Baja California, Mexico 2 21 December 25.2 2.2× Compton California, United States 1 24 December 17.6 2.1× Torrance California, United States 1 23 December 11.8 2.1× Hanford California, United States 1 23 December 17.3 2.1× Calexico California, United States 1 24 December 13.0 2.1× Anaheim California, United States 1 21 December 13.0 2.0× Hawthorne California, United States 1 23 December 14.4 2.0× Bakersfield California, United States 1 20 December 19.9 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 39 of 142 episodes in the United States and Mexico since our records began, by cities reached.
North-eastern United States and Canada, June and July 2023 280 North-eastern United States and Canada, July 2026 264 North-eastern United States and Canada, May and June 2023 261 North-eastern United States and Canada, July and August 2025 241 North-eastern United States and Canada, July 2023 240 North-eastern United States and Canada, June 2025 196 North-eastern United States and Canada, June 2023 161 North-eastern United States and Canada, July 2025 119 North-western United States and Canada, August 2023 110 North-eastern United States, June 2025 104 North-western United States and Canada, August 2026 99 North-eastern United States and Canada, February 2026 96 Western United States, December 2024 25 Bars: cities reached; colour: the level of the episode's highest daily reading. All 142 .
Use this page SmogRank, Western United States, December 2024: 25 cities with PM2.5 at twice their usual or more, 20 to 24 December 2024, smogrank.com/episodes/2024-12-western-united-states (accessed 3 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.
