Mexico City Air Quality: Which Months Are Worst, and What Our PM2.5 Data Shows

When is the air worst in Mexico City?

In the dry season, and the main problem is ozone, not the fine particles we measure. Mexico News Daily's reports on high ozone levels describe it building when the wind drops, humidity is low and the sun is strong; another account puts the season at February to June, ending with the first rains. Alerts and contingencies are called mostly in March, April and May, and the metropolitan environment commission forecast five to 11 ozone contingencies for the 2026 season (in Spanish).

Our data does not measure ozone, so it cannot confirm that season. It measures PM2.5, fine particles, from the CAMS model through Open-Meteo for central Mexico City, averaged over 2023, 2024 and 2025, with three cleaner bases under it:

For particles the picture is flat. Mexico City's monthly average is between 20 and 28 µg/m³ all year, above the WHO daily guideline of 15 in every month, with May (28), February (27) and December (27) highest. There is no clean season, but also no dramatic one. In the cooler dry months, November to February, temperature inversions also hold particles near the ground, so the dry season is not better for particles either.

Where to be next: your month-by-month route, $19

A route for your months with a leave-by date for each stop, a backup, and the seasonal traps on your path. Drafted from 11 years of weather data, every number checked against it, in your inbox within 48 hours. Not included: visas, insurance or bookings.

See a sample plan Get my plan, $19

What is ozone, and why does it matter for planning?

Ground-level ozone is not emitted directly. It forms when vehicle and industrial emissions react in strong sunshine, which is why it peaks in the dry, sunny months and is worst in the afternoon, not the morning. Mexico City has plenty of sun at altitude and a basin that traps air, so the dry season is when the city issues its alerts and, on the worst days, restricts traffic and industry. The rains, which usually start in June, bring cloud and a clean-out.

For a nomad this is a different problem from smoke. It does not show as a haze you can see, and it does not follow the same months as the particle strip above. A stay from June to November avoids the ozone season, though afternoon thunderstorms are routine then. March to May is the best weather for walking around but the highest ozone, so check the city's live air index each day and keep outdoor plans for the morning.

Does it change from year to year?

Yes. February averaged 28 in 2023, 19 in 2024 and 35 in 2025, and December went from 20 to 28 to 33. July 2025 stands out, at 35 with 18 days above 35 µg/m³, and December 2025 also had 18 such days. The model also reads low on bad days (it averages an area about 45 km across), so real peaks are higher.

Where is the air cleaner in Mexico?

Southern and coastal places, by a wide margin, as the strip shows. Mérida and Playa del Carmen read 8 to 11 µg/m³ from February to May and Oaxaca 6 to 18, against 22 to 28 for Mexico City. Weather is the other half of the choice: see our Mexico City weather guide for temperature and rain, and note that the coast is hot and humid in the rainy season. None of the three has Mexico City's ozone problem in the sources we read, because ozone needs the traffic and industry of a large basin to build, but we have no ozone data for them either, so that is a reasonable expectation and not a measurement. If you split the year, the simplest plan is the capital from June to November and the south or the coast from February to May.

Where to go instead: three cleaner bases

• Mérida

  35° high in Apr23 mm in Apr

  8 to 11 µg/m³ from February to May, well under half of Mexico City's level. Hot in spring, but a city with services and a settled nomad scene.

  Suits: people who want a real city with clean air and can take April heat

• Playa del Carmen

  29° high in Apr48 mm in Apr

  8 to 9 µg/m³ from February to May, among the cleanest in spring. Humid in the wet months, with sea wind all year.

  Suits: people who want a beach base in the months when Mexico City's ozone peaks

• Oaxaca

  31° high in Apr30 mm in Apr

  6 to 18 µg/m³ across the same months, rising to its yearly high in May. A mountain city at altitude like Mexico City, with a far smaller footprint.

  Suits: people who want the altitude and the culture without the capital's basin

How would you plan around it?

1. If ozone worries you, avoid March to May in Mexico City, or spend those weeks on the coast.
2. June to November is gentler for ozone and flat for particles, though it is the rainy season.
3. Do not read our strip as the whole story. For ozone, check the city's own air-quality index before you book.
4. Pair this page with the weather. The weather guide shows the dry months are also the warmest and sunniest, the same combination that drives ozone, so the best walking weather and the worst ozone overlap.
5. Remember the altitude. Mexico City is at about 2,240 m, which affects how you feel, separate from air quality.

We give no health advice here. If you are sensitive to polluted air, speak to a doctor before planning a long stay.

About this data

Daily PM2.5 averaged by month from the CAMS global model through Open-Meteo, mean of 2023 to 2025, one point per city. Ozone is not included. A model cannot see a single road or a bad hour, and reads low on bad days.