Air Quality in Mexico City: How It Affects Your Breathing

Name: Air Quality in Mexico City and Your Breathing
Creator: Dr. William César Lara Vázquez

Is Mexico City's air quality affecting your breathing?

Valley air can be crystal clear one morning, then sting your throat by mid afternoon. Learn to read CDMX's pollution index, know which dates turn rough, why that happens, plus which symptoms deserve a lung specialist's attention.

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Make sense of CDMX's air index

One index, two names

CDMX's Índice Aire y Salud, successor to IMECA: one number, one color, green to purple. Check aire.cdmx.gob.mx (SIMAT stations) or any AQI app.

Green or yellow

Clean or acceptable air: run outside, bike, open windows. Most days land here, especially once summer rains arrive.

Orange

Bad for sensitive groups: asthma, COPD, pregnancy, 60+ or small children. Shorten outdoor exertion, avoid the 1-to-5 pm peak.

Red or purple

Bad for everyone: move exercise indoors, close windows until evening. This is contingencia territory.

Rough days, explained

Ozone season: March to May

Spring sunshine cooks vehicle emissions into ozone, peaking early-to-mid afternoon. Most alerts cluster here, plan outdoor time before lunch.

Winter thermal inversions

Cold, windless mornings from November through February trap fine particles near the ground until midday sun stirs them loose.

Geography works against you

Mountains ring the valley, so stagnant air can't drain. Thin air at 2,240 m adds its own challenge: altitude and breathing in Mexico City.

What triggers an alert

Ozone or PM2.5 past official thresholds: CAMe activates a contingencia, extra driving restrictions and sensitive groups asked indoors. Full guide in Spanish →

Smart habits for bad-air days

Exercise early

Ozone bottoms out around sunrise; get your run done before late morning. Orange showing? Take workouts indoors.

Ventilate at dawn, seal by lunch

Windows open at daybreak, shut roughly 1 to 7 pm on smoggy afternoons. June-to-October rains scrub the sky daily.

Reliever within reach

Don't skip maintenance doses, and carry your reliever inhaler with you. Smoggy afternoons punish medication left behind.

Check before you plan

Ten seconds on today's index: park morning or museum afternoon? During alerts, Hoy No Circula driving restrictions expand.

When it's harmless, when it's urgent

Usually harmless

Itchy eyes, scratchy throat, a mild dry cough that eases indoors. Annoying, yet it settles without treatment.

Get medical help now

Struggling to breathe while sitting still
Chest pressure or pain
Wheezing your reliever can't calm
Lips or nail beds turning bluish
A pulse-ox reading under 90%
New confusion or unusual drowsiness

Dr. William César Lara Vázquez

Pulmonologist (Neumólogo) · Advanced COPD specialization (in progress)

Pulmonology: National Institute of Respiratory Diseases (INER), Mexico's national referral center.
500+ pulmonology consultations personally handled in 2025 in Mexico City, each with a treatment plan explained to the patient.
Advanced COPD specialization in progress: ongoing clinical training in obstructive lung disease.
Current board certification by the Consejo Nacional de Neumología (CNN-2102).
Clinical practice at Hospital Santa Coleta, with spirometry, FeNO, home sleep testing and pleural procedures interpreted directly.

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Common questions, answered

Is the air quality in Mexico City bad?

It varies a lot by season and by day. Many days are moderate, and some are genuinely clean, especially after rain. The rough stretches are ozone season from March to May and cold winter mornings, when fine particles get trapped over the valley. Healthy visitors usually notice little; people with asthma or sensitive airways should check the daily index.

What is a contingencia ambiental (environmental alert)?

It is an official emergency alert issued when ozone or PM2.5 pollution passes set thresholds in the Valley of Mexico. Authorities restrict driving, suspend outdoor school sports and ask sensitive groups to stay indoors. If you hear one is active, keep outdoor plans light, close windows during the afternoon and follow the local index until it lifts.

Can I exercise outdoors in Mexico City?

Yes, on most days. The smart window is early morning, before ozone builds up; the worst window is roughly 1 to 5 pm during ozone season. Check the air index first: green or yellow means go, orange means take it easier if your airways are sensitive, and on red days or during an alert move your workout indoors.

Should I wear a mask on high-pollution days?

Only a well-fitted N95 or KN95 actually filters fine particles; cloth and surgical masks do not, and no mask filters ozone. For most visitors a mask is unnecessary. It makes sense if you have asthma or COPD and must spend time outdoors during an alert. Limiting time outside in the afternoon protects you more than any mask.

Is Mexico City's air quality affecting your breathing?

Make sense of CDMX's air index