Mexico City, Mexico Air Quality & Smog

Dominant pollutants, when pollution and smog are worst, a notable historical episode, and the official monitoring agencies for Mexico City, Mexico — plus how to check the current reading. Mexico City reports air quality on the Mexico’s air-quality index (IMECA / Aire y Salud), not the US AQI — our guide to world air-quality indices explains how the major scales compare.

Dominant pollutants

Ozone, PM2.5.

Seasonal pattern: when smog is worst

Mexico City sits in a high-altitude basin at about 2,240 m, ringed by mountains that trap pollution and where thinner air worsens combustion. Once labelled the world's most polluted city, it has improved dramatically through decades of policy (Hoy No Circula driving restrictions, the ProAire programmes). Ozone remains the warm-season challenge; regional wildfire smoke can spike PM2.5.

A notable air-quality episode

In May 2019, wildfire smoke from surrounding states combined with ozone to trigger an environmental contingency that closed schools and restricted activity across the Valley of Mexico — a reminder that the basin's air can still deteriorate sharply.

The local index and who runs it

Mexico City reports air quality using the Mexico’s air-quality index (IMECA / Aire y Salud), not the US AQI — so the same air can read as a different number than you may be used to. Mexico City reports the IMECA-based Índice Aire y Salud through SEDEMA's SIMAT network; see our world air-quality indices guide for context.

• SEDEMA (Mexico City environment secretariat)
• SIMAT (city monitoring network)

How to check air quality in Mexico City

For the official live reading, the agency portals above are the canonical source. To understand what the numbers mean, see our guide to world air-quality indices and how they compare to the US AQI. Smog Report puts glanceable air quality on your iPhone — widgets, Live Activities, Siri, and Apple Watch — free and with no account.

Common questions about Mexico City air quality

Why does Mexico City have air-quality and smog problems?

Mexico City sits in a high-altitude basin at about 2,240 m, ringed by mountains that trap pollution and where thinner air worsens combustion. Once labelled the world's most polluted city, it has improved dramatically through decades of policy (Hoy No Circula driving restrictions, the ProAire programmes). Ozone remains the warm-season challenge; regional wildfire smoke can spike PM2.5.

What are the main air pollutants in Mexico City?

Mexico City's dominant pollutants are ozone, PM2.5. The reading on any given day is usually driven by whichever of these is highest.

Has Mexico City had a major air-quality or smog event?

In May 2019, wildfire smoke from surrounding states combined with ozone to trigger an environmental contingency that closed schools and restricted activity across the Valley of Mexico — a reminder that the basin's air can still deteriorate sharply.

What air-quality index does Mexico City use?

Mexico City reports air quality on the Mexico’s air-quality index (IMECA / Aire y Salud) (index), not the US AQI — so the same air can read as a different number than you may be used to. For live, glanceable readings on your iPhone, the free Smog Report app auto-selects the right local index for wherever you are.

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