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🇲🇽 Mexico City

SIMAT Air Monitoring and the Valley of Mexico Contingency Programme

Mexico City has sampled its air since 1966 and has run the automatic RAMA network since 1986, when 25 stations began reporting ozone, carbon monoxide, sulphur dioxide and nitrogen oxides hourly. Since 2016 a reading of 155 ppb of ozone triggers a Phase I contingency, declared not by the city but by CAMe, the federal-state commission for the metropolitan area. The declaration binds: the Hoy No Circula ban doubles from 05:00 to 22:00, factories must cut ozone-precursor emissions by 40%, sites over 5,000 square metres stop building, and the Tula refinery is capped at 75% of process capacity. Whether the emergency lever itself works is contested.

Live 📅 since 1986 ✔ Editor-reviewed

✔ Reviewed by the 1001 Smart Cities editorial desk · 🔎 Last verified

🌱 EnvironmentAir qualitySensors & IoTOpen dataTraffic management

📊 Impact

Particulate pollution across Mexico City has fallen 60.4% since the 1990 ProAire programme began, which AQLI (University of Chicago) puts at 3.3 years of life expectancy — but that is the long-run policy mix (unleaded fuel, catalytic converters, fuel switching, transit), not the contingency mechanism. The Phase I ozone trigger has only ever been tightened, from 180 to 150 IMECA points in April 2016 and holding at 155 ppb since. On the emergency lever itself, peer-reviewed work finds no measurable air-quality benefit: the Saturday extension of Hoy No Circula had no discernible effect across eight pollutants, and drivers responded by buying second, older cars.

🎓 Lesson

A measured value with legal force is only as good as the lever it pulls. Mexico City has the oldest such trigger in the atlas and has never loosened it — yet the peer-reviewed evidence says the driving ban it reaches for does not clean the air.

Evidence🔬 Peer-reviewed
Scale🗺️ Regional

Sources

↗ SIMAT — Direccion de Monitoreo Atmosferico, SEDEMA CDMX (operator)Operator site for the network and the hourly index. Returned 503 to automated fetching throughout this review; content verified indirectly. Do not cite a data licence from it — none was readable.
↗ La situacion actual del sistema de monitoreo ambiental en la ZMVM — Investigaciones Geograficas, UNAM (peer-reviewed)Network history: 'En 1966 ... se instalo la primera red de monitoreo con 4 estaciones con equipos manuales'; 'En 1986 se inicio la operacion de la Red Automatica de Monitoreo Atmosferico (RAMA) con 25 estaciones y equipos automaticos para medir monoxido de carbono, dioxido de azufre, oxidos de nitrogeno y ozono' (In 1966 the first monitoring network was installed with 4 manual stations; in 1986 RAMA began operating with 25 automatic stations measuring CO, SO2, NOx and ozone).
↗ Acuerdo — Programa para Prevenir y Responder a Contingencias Ambientales Atmosfericas en la ZMVM, Periodico Oficial del Estado de Mexico, 28 May 2019 (instrument)The governing instrument, published the same day in the Gaceta Oficial de la CDMX and the Periodico Oficial del Estado de Mexico. File exists at this URL; direct fetch returned 503 during review, so the thresholds and measures below are sourced from the CAMe communiques that apply it.
↗ Contingencias ambientales en el valle de Mexico: guia basica — Grupo Animal (independent explainer)Threshold, verbatim: Phase I activates at 'concentraciones de ozono superiores a 155 ppb (partes por billon)' (ozone concentrations above 155 ppb), against an air-quality standard of 'no rebasar 90 partes por billon, durante una hora'. Also documents that the trigger has been progressively lowered since 1990, never raised.
↗ Se mantiene la Fase I de contingencia ambiental en ZMVM — News Report MX, reproducing the CAMe communique (press)The mandatory measures, verbatim from the CAMe communique: industry 'reduciran el 40% de sus emisiones de precursores de ozono' (will cut ozone-precursor emissions by 40%); the Miguel Hidalgo refinery at Tula 'no operara a mas del 75% de capacidad del total de proceso'; the Francisco Perez Rios thermoelectric plant 'Reduccion del 30% del consumo de combustoleo'; private vehicles off the road 'de las 5:00 a las 22:00 horas'.
↗ Activan contingencia ambiental por ozono en la ZMVM: restricciones y doble Hoy No Circula — TV Azteca (press)Declaring body and a worked example: the 'Comision Ambiental de la Megalopolis (CAMe)' activated Phase 1 on a 'concentracion maxima de ozono' of 160 ppb at the Cuajimalpa (CUA) station, banning hologram 2 vehicles outright plus hologram 1 and 0/00 by plate digit, 05:00 to 22:00.
↗ Saturday Driving Restrictions Fail to Improve Air Quality in Mexico City — Davis, Scientific Reports (2017) (peer-reviewed)Finds the Saturday expansion of Hoy No Circula had virtually no discernible effect on pollution across eight major pollutants, against ex-ante predictions of a 15%+ emissions cut. nature.com blocked automated fetching (auth redirect); finding confirmed at title and abstract level.
↗ Driving Restriction and Air Quality in Mexico City — Resources for the Future, on Davis, Journal of Political Economy (2008) (independent)Verbatim: 'When hourly air pollution records from monitoring stations were examined, they showed no evidence that the program has improved air quality'; mechanism: 'no one got out of their cars. Instead, the evidence indicates that HNC has led to an increase in the total number of vehicles in circulation', many of them high-emission used imports.
↗ Mexico City: ProAire (1990) — Air Quality Life Index, EPIC, University of Chicago (independent)Verbatim: 'particulate pollution has declined by 60.4% since the introduction of the 1990 ProAire policies'; 'In terms of life expectancy, that implies a difference of 3.3 years'. AQLI credits the ProAire policy sequence (catalytic converters, unleaded petrol, fuel switching, transit), not the contingency programme.
↗ Spatio-Temporal Representativeness of Air Quality Monitoring Stations in Mexico City — Frontiers in Public Health (2020) (peer-reviewed)Independent test of network coverage over 49 SIMAT stations and nine pollutants, 2009-2018. Verbatim: 'the distribution and the number of the monitoring stations is sufficient to evaluate the majority of pollutants, with the exception of sulfur dioxide (SO2)', where the shortfall is 'constrained to the southern part' of the city.
📎 Cite this project

1001 Smart Cities (2026). “SIMAT Air Monitoring and the Valley of Mexico Contingency Programme” — Mexico City, Mexico. The Smart City Atlas. https://1001smartcities.org/projects/mexico-city-air-quality-contingency/ (last verified 2026-07-26). Data: CC BY 4.0.

The underlying data is free to reuse with attribution — see the open data page.

🔗 Related projects

🇲🇽 Hoy No Circula: Mexico City's Plate-Based Driving Restriction · Mexico City The lever this trigger pulls: a Phase I doubles the 1989 plate ban — and the peer-reviewed record says the ban never cleaned the air. 🇮🇳 GRAP: Air Quality Readings as a Legal Trigger · New Delhi Delhi gave an AQI reading legal force in 2017; Mexico City has measured hourly since 1986 and its ozone trigger has only tightened. 🇮🇩 Court-Ordered Air Quality Monitoring · Jakarta Jakarta's court-built network triggers nothing; Mexico City's 155 ppb halts large building sites and caps a refinery at 75%. 🇺🇸 Miami-Dade's Chief Heat Officer and Extreme Heat Action Plan · Miami Miami-Dade's heat threshold fires an advisory the state stripped of any duty; Mexico City's ozone threshold binds industry by law.

🧭 Explore the atlas

🏙️ Mexico City Explore every verified project and the city's smart-city story. 🌱 Environment Browse the main topic behind this project. 📖 Adaptive traffic signals Traffic lights that retime themselves in real time from live sensor data to match actual traffic, instead of running a fixed pre-set schedule. 📖 Low-emission zone An area where the most polluting vehicles are charged or banned, based on their emissions standard, to improve urban air quality. 📖 Open data Information anyone is free to access, use and share, published by governments in machine-readable formats under an open licence. 🏙️ Urban digital twins compared: Singapore, Tokyo, Seoul and Rotterdam Read the wider analysis and comparison. 🚦 Asphalt or algorithms Read the wider analysis and comparison.

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