SmogRank / Episodes / United States

South-western United States, May 2026

For 2 days, from 17 to 18 May 2026, 12 cities in the United States and Mexico had PM2.5 at least twice their usual for the time of year. The worst reading was Torrance, California, United States: 40.2 µg/m³ on 18 May, about 4.9× its usual 8.2.

No cause namedWe have no fire or smoke records for these days, so we only say what the measurements show.
Cities reached12in 2 countries
Days217 to 18 May 2026
Worst day17 May8 cities counted
Furthest above usual5.3×Huntington Beach

Day by day

17 May 8 cities at twice their usual or more
TemeculaEncinitasLake ElsinoreBanningMission ViejoRiversideJurupa ValleyIndioFontanaAnaheimDiamond BarGlendoraWhittierVictorvilleCarsonLomitaPasadenaLos AngelesEl CentroHawthorneInglewoodLa Crescenta-MontroseBurbankMexicaliLancasterSanta ClaritaAgouraSimi ValleyThousand OaksFillmoreOxnardYumaRidgecrestBakersfieldSanta BarbaraGoletaLompocOrcuttNipomoArroyo GrandeSan Luis ObispoAtascaderoPrescottGlendaleTijuanaSanta MonicaComptonCalexicoEl CajonPowaySan DiegoChula VistaLong BeachOceansideTorranceHuntington Beach
14 May15161718192021
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

CalexicoCalexico, 14 May: 24.0 µg/m³, 2.4× usualCalexico, 15 May: 33.7 µg/m³, 3.4× usualCalexico, 16 May: 26.7 µg/m³, 2.7× usualCalexico, 17 May: 29.5 µg/m³, 3.0× usualCalexico, 18 May: 28.4 µg/m³, 2.8× usualCalexico, 19 May: 24.3 µg/m³, 2.4× usualCalexico, 20 May: 21.9 µg/m³, 2.2× usualCalexico, 21 May: 24.8 µg/m³, 2.5× usualHuntington BeachHuntington Beach, 14 May: 1.9 µg/m³, 0.3× usualHuntington Beach, 15 May: 3.7 µg/m³, 0.7× usualHuntington Beach, 16 May: 7.4 µg/m³, 1.3× usualHuntington Beach, 17 May: 28.0 µg/m³, 5.0× usualHuntington Beach, 18 May: 29.9 µg/m³, 5.3× usualHuntington Beach, 19 May: 26.7 µg/m³, 4.8× usualHuntington Beach, 20 May: 22.3 µg/m³, 4.0× usualHuntington Beach, 21 May: 14.7 µg/m³, 2.6× usualPowayPoway, 14 May: 6.2 µg/m³, 0.7× usualPoway, 15 May: 9.1 µg/m³, 1.1× usualPoway, 16 May: 8.2 µg/m³, 1.0× usualPoway, 17 May: 27.9 µg/m³, 3.3× usualPoway, 18 May: 17.5 µg/m³, 2.1× usualPoway, 19 May: 16.1 µg/m³, 1.9× usualPoway, 20 May: 18.5 µg/m³, 2.2× usualPoway, 21 May: 17.8 µg/m³, 2.1× usualSan DiegoSan Diego, 14 May: 6.1 µg/m³, 0.7× usualSan Diego, 15 May: 7.1 µg/m³, 0.9× usualSan Diego, 16 May: 10.4 µg/m³, 1.3× usualSan Diego, 17 May: 27.8 µg/m³, 3.4× usualSan Diego, 18 May: 16.8 µg/m³, 2.0× usualSan Diego, 19 May: 20.0 µg/m³, 2.4× usualSan Diego, 20 May: 24.4 µg/m³, 3.0× usualSan Diego, 21 May: 18.4 µg/m³, 2.2× usualOceansideOceanside, 14 May: 5.6 µg/m³, 0.8× usualOceanside, 15 May: 6.3 µg/m³, 0.9× usualOceanside, 16 May: 8.5 µg/m³, 1.2× usualOceanside, 17 May: 27.6 µg/m³, 3.9× usualOceanside, 18 May: 15.4 µg/m³, 2.2× usualOceanside, 19 May: 18.2 µg/m³, 2.6× usualOceanside, 20 May: 20.7 µg/m³, 2.9× usualOceanside, 21 May: 16.2 µg/m³, 2.3× usualEl CajonEl Cajon, 14 May: 6.0 µg/m³, 0.7× usualEl Cajon, 15 May: 8.8 µg/m³, 1.0× usualEl Cajon, 16 May: 9.2 µg/m³, 1.1× usualEl Cajon, 17 May: 27.1 µg/m³, 3.2× usualEl Cajon, 18 May: 15.3 µg/m³, 1.8× usualEl Cajon, 19 May: 13.7 µg/m³, 1.6× usualEl Cajon, 20 May: 17.9 µg/m³, 2.1× usualEl Cajon, 21 May: 16.0 µg/m³, 1.9× usualTijuanaTijuana, 14 May: 7.0 µg/m³, 0.6× usualTijuana, 15 May: 10.1 µg/m³, 0.9× usualTijuana, 16 May: 13.1 µg/m³, 1.1× usualTijuana, 17 May: 26.3 µg/m³, 2.3× usualTijuana, 18 May: 19.2 µg/m³, 1.7× usualTijuana, 19 May: 18.0 µg/m³, 1.6× usualTijuana, 20 May: 25.6 µg/m³, 2.2× usualTijuana, 21 May: 20.8 µg/m³, 1.8× usualChula VistaChula Vista, 14 May: 5.7 µg/m³, 0.7× usualChula Vista, 15 May: 7.6 µg/m³, 1.0× usualChula Vista, 16 May: 10.4 µg/m³, 1.4× usualChula Vista, 17 May: 26.0 µg/m³, 3.4× usualChula Vista, 18 May: 16.4 µg/m³, 2.1× usualChula Vista, 19 May: 16.0 µg/m³, 2.1× usualChula Vista, 20 May: 22.5 µg/m³, 2.9× usualChula Vista, 21 May: 17.1 µg/m³, 2.2× usualTorranceTorrance, 14 May: 2.1 µg/m³, 0.3× usualTorrance, 15 May: 4.5 µg/m³, 0.5× usualTorrance, 16 May: 8.0 µg/m³, 1.0× usualTorrance, 17 May: 21.0 µg/m³, 2.6× usualTorrance, 18 May: 40.2 µg/m³, 4.9× usualTorrance, 19 May: 34.3 µg/m³, 4.2× usualTorrance, 20 May: 17.6 µg/m³, 2.1× usualTorrance, 21 May: 11.3 µg/m³, 1.4× usualSanta MonicaSanta Monica, 14 May: 6.4 µg/m³, 0.6× usualSanta Monica, 15 May: 7.4 µg/m³, 0.7× usualSanta Monica, 16 May: 8.6 µg/m³, 0.8× usualSanta Monica, 17 May: 18.3 µg/m³, 1.7× usualSanta Monica, 18 May: 28.3 µg/m³, 2.7× usualSanta Monica, 19 May: 29.8 µg/m³, 2.8× usualSanta Monica, 20 May: 20.1 µg/m³, 1.9× usualSanta Monica, 21 May: 11.6 µg/m³, 1.1× usualLong BeachLong Beach, 14 May: 5.8 µg/m³, 0.8× usualLong Beach, 15 May: 6.9 µg/m³, 1.0× usualLong Beach, 16 May: 10.3 µg/m³, 1.5× usualLong Beach, 17 May: 21.5 µg/m³, 3.1× usualLong Beach, 18 May: 25.5 µg/m³, 3.6× usualLong Beach, 19 May: 20.2 µg/m³, 2.9× usualLong Beach, 20 May: 16.7 µg/m³, 2.4× usualLong Beach, 21 May: 16.0 µg/m³, 2.3× usualComptonCompton, 14 May: 7.7 µg/m³, 0.8× usualCompton, 15 May: 9.3 µg/m³, 1.0× usualCompton, 16 May: 12.8 µg/m³, 1.4× usualCompton, 17 May: 21.9 µg/m³, 2.4× usualCompton, 18 May: 25.0 µg/m³, 2.7× usualCompton, 19 May: 22.0 µg/m³, 2.4× usualCompton, 20 May: 20.2 µg/m³, 2.2× usualCompton, 21 May: 16.5 µg/m³, 1.8× usual14 May15161718192021
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
Huntington BeachCalifornia, United States2 29.918 May5.65.3×
TorranceCalifornia, United States1 40.218 May8.24.9×
OceansideCalifornia, United States1 27.617 May7.13.9×
Long BeachCalifornia, United States1 25.518 May7.03.6×
San DiegoCalifornia, United States1 27.817 May8.23.4×
Chula VistaCalifornia, United States1 26.017 May7.73.4×
CalexicoCalifornia, United States2 33.715 May10.03.4×
PowayCalifornia, United States1 27.917 May8.43.3×
El CajonCalifornia, United States1 27.117 May8.63.2×
Santa MonicaCalifornia, United States1 29.819 May10.62.8×
ComptonCalifornia, United States1 25.018 May9.22.7×
TijuanaBaja California, Mexico1 26.317 May11.42.3×

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 and Mexico

Number 63 of 106 episodes in the United States and Mexico since our records began, by cities reached.

Bars: cities reached; colour: the level of the episode's highest daily reading. All 106.

Use this page

SmogRank, South-western United States, May 2026: 12 cities with PM2.5 at twice their usual or more, 17 to 18 May 2026, smogrank.com/episodes/2026-05-south-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.