SmogRank / Episodes / Mexico

Northern Mexico and United States, March and April 2025

For 3 days, from 30 March to 1 April 2025, 8 cities in Mexico and the United States had PM2.5 at least twice their usual for the time of year. The worst reading was Saltillo, Coahuila, Mexico: 111.0 µg/m³ on 31 March, about 6.2× its usual 17.8.

No cause namedWe have no fire or smoke records for these days, so we only say what the measurements show.
Cities reached8in 2 countries
Days330 March to 1 April 2025
Worst day31 March5 cities counted
Furthest above usual6.2×Saltillo

Day by day

31 March 5 cities at twice their usual or more
MissionCiudad Benito JuárezCiudad General EscobedoJardines de la SillaSanta CatarinaGarcíaSan AntonioGalvestonMonterreyCadereyta JiménezHeroica MatamorosEdinburgLaredoCorpus ChristiEagle PassSaltillo
27 Mar282930311 Apr234
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

Corpus ChristiCorpus Christi, 27 March: 12.8 µg/m³Corpus Christi, 28 March: 9.3 µg/m³Corpus Christi, 29 March: 23.0 µg/m³Corpus Christi, 30 March: 31.1 µg/m³, 3.5× its usual 8.8Corpus Christi, 31 March: 31.1 µg/m³, 3.5× its usual 8.9Corpus Christi, 1 April: 23.5 µg/m³Corpus Christi, 2 April: 27.5 µg/m³Corpus Christi, 3 April: 29.4 µg/m³Corpus Christi, 4 April: 27.2 µg/m³EdinburgEdinburg, 27 March: 4.7 µg/m³Edinburg, 28 March: 5.6 µg/m³Edinburg, 29 March: 20.3 µg/m³Edinburg, 30 March: 27.9 µg/m³, 2.9× its usual 9.5Edinburg, 31 March: 30.6 µg/m³, 3.2× its usual 9.6Edinburg, 1 April: 24.7 µg/m³Edinburg, 2 April: 23.0 µg/m³Edinburg, 3 April: 21.4 µg/m³Edinburg, 4 April: 21.8 µg/m³Heroica MatamorosHeroica Matamoros, 27 March: 7.4 µg/m³Heroica Matamoros, 28 March: 7.7 µg/m³Heroica Matamoros, 29 March: 22.4 µg/m³Heroica Matamoros, 30 March: 27.7 µg/m³, 3.1× its usual 9.0Heroica Matamoros, 31 March: 28.5 µg/m³, 3.1× its usual 9.3Heroica Matamoros, 1 April: 16.3 µg/m³Heroica Matamoros, 2 April: 20.8 µg/m³Heroica Matamoros, 3 April: 18.8 µg/m³Heroica Matamoros, 4 April: 17.6 µg/m³LaredoLaredo, 27 March: 3.2 µg/m³Laredo, 28 March: 5.5 µg/m³Laredo, 29 March: 10.3 µg/m³Laredo, 30 March: 25.9 µg/m³, 2.8× its usual 9.3Laredo, 31 March: 28.2 µg/m³, 3.0× its usual 9.3Laredo, 1 April: 31.3 µg/m³, 3.3× its usual 9.4Laredo, 2 April: 20.0 µg/m³Laredo, 3 April: 19.1 µg/m³Laredo, 4 April: 19.7 µg/m³SaltilloSaltillo, 27 March: 31.1 µg/m³Saltillo, 28 March: 15.2 µg/m³Saltillo, 29 March: 13.8 µg/m³Saltillo, 30 March: no readingSaltillo, 31 March: 111.0 µg/m³, 6.2× its usual 17.8Saltillo, 1 April: no readingSaltillo, 2 April: 10.0 µg/m³Saltillo, 3 April: 5.1 µg/m³Saltillo, 4 April: 8.5 µg/m³MonterreyMonterrey, 27 March: no readingMonterrey, 28 March: no readingMonterrey, 29 March: no readingMonterrey, 30 March: no readingMonterrey, 31 March: 28.0 µg/m³Monterrey, 1 April: 38.6 µg/m³, 2.2× its usual 17.4Monterrey, 2 April: 30.5 µg/m³Monterrey, 3 April: 23.0 µg/m³Monterrey, 4 April: 25.6 µg/m³Cadereyta JiménezCadereyta Jiménez, 27 March: no readingCadereyta Jiménez, 28 March: no readingCadereyta Jiménez, 29 March: no readingCadereyta Jiménez, 30 March: no readingCadereyta Jiménez, 31 March: 28.8 µg/m³Cadereyta Jiménez, 1 April: 34.4 µg/m³, 2.3× its usual 14.8Cadereyta Jiménez, 2 April: 36.3 µg/m³Cadereyta Jiménez, 3 April: 26.6 µg/m³Cadereyta Jiménez, 4 April: 21.5 µg/m³Eagle PassEagle Pass, 27 March: 2.0 µg/m³Eagle Pass, 28 March: 3.3 µg/m³Eagle Pass, 29 March: 7.9 µg/m³Eagle Pass, 30 March: 20.7 µg/m³Eagle Pass, 31 March: 19.6 µg/m³Eagle Pass, 1 April: 28.9 µg/m³, 3.8× its usual 7.7Eagle Pass, 2 April: 25.1 µg/m³Eagle Pass, 3 April: 22.7 µg/m³Eagle Pass, 4 April: 9.7 µg/m³27 Mar282930311 Apr234
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
SaltilloCoahuila, Mexico1 111.031 March17.86.2×
Eagle PassTexas, United States1 28.91 April7.73.8×
Corpus ChristiTexas, United States2 31.130 March8.83.5×
LaredoTexas, United States3 31.31 April9.43.3×
EdinburgTexas, United States2 30.631 March9.63.2×
Heroica MatamorosTamaulipas, Mexico2 28.531 March9.33.1×
Cadereyta JiménezNuevo León, Mexico1 34.41 April14.82.3×
MonterreyNuevo León, Mexico1 38.61 April17.42.2×

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 Mexico and the United States

Number 129 of 141 episodes in Mexico and the United States since our records began, by cities reached.

Bars: cities reached; colour: the level of the episode's highest daily reading. All 141.

Use this page

SmogRank, Northern Mexico and United States, March and April 2025: 8 cities with PM2.5 at twice their usual or more, 30 March to 1 April 2025, smogrank.com/episodes/2025-03-northern-mexico-and-united-states (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.