Critical Episode Management: A Next-Day Forecast With Legal Force
Every winter from 1 May to 31 August, Santiago manages its air by forecast rather than by reading. The Seremi del Medio Ambiente for the Region Metropolitana watches ten automatic MACAM stations and runs the Cassmassi model — a multiple linear regression proposed in 1999 — to predict the next day's maximum 24-hour particulate average. If the prediction crosses a threshold fixed in the decontamination plan, the Delegacion Presidencial Regional declares an Alerta, Preemergencia or Emergencia for the following day, and legal duties follow: wood-burning heaters barred across the whole region, pellet heaters too from Preemergencia upward, additional number plates taken off the road, listed industrial plants halted, school sport moved indoors. So the threshold binds but the day is judged — the declaration is an act of an appointed regional authority on the environment secretariat's recommendation, not an automatic consequence of a measured value. Chile's environment ministry dates the regime to the first plan in 1997; the current instrument, Supreme Decree 31/2016, has been in force since 2018, and Fundacion Terram points out it was meant to be revised in 2022. The industrial lever has quietly emptied itself: for the 2026 season the environmental regulator listed one of 55 affected large establishments as obliged to stop.
📊 Impact
The environment ministry counts 314 hours in fine-particulate episodes in the Region Metropolitana in 2025 against 915 in 2015, a 66% fall over the decade, and 23 declared episodes in 2025 — 20 alerts and 3 pre-emergencies — the third-best winter since the plan began operating (MMA balance, 2025). The same balance reports vehicle-restriction violations down 23% on 2024, wood-heater violations down 88%, illegal agricultural burns down 23.8% in number and 77.6% in area burnt, and 98% of large industrial facilities meeting their particulate reduction goals; every one of these is ministry self-reporting. Meteorology still dominates the annual count: by 16 June 2026 the region had recorded 16 episodes (13 alerts, 3 pre-emergencies) against one at the same date in 2025 and none in 2024, in a season running a 79.2% rainfall deficit (Fundacion Terram, 16 June 2026). No peer-reviewed study isolates the episode regime itself. Jorquera (Urban Climate, 2021) finds a meteorologically adjusted downward PM2.5 trend across Chilean cities that have management plans, but that is the plan as a whole, not its episode days. Barraza et al. (Atmospheric Chemistry and Physics, 2017) found wood burning at 12.3% of downtown PM2.5 and, unlike four other sources, showing no significant change between 1998 and 2012.
🎓 Lesson
A threshold can be fixed in law and still leave the decision human: Santiago acts on a prediction of tomorrow, signed by a presidentially appointed regional authority. And the lever that looks hardest is the emptiest — meeting the plan's emission targets releases a plant from the shutdown list, so by 2026 only one of 55 remained on it.
Sources
📎 Cite this project
1001 Smart Cities (2026). “Critical Episode Management: A Next-Day Forecast With Legal Force” — Santiago, Chile. The Smart City Atlas. https://1001smartcities.org/projects/santiago-air-quality-episodes/ (last verified 2026-07-26). Data: CC BY 4.0.
The underlying data is free to reuse with attribution — see the open data page.
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