By 2035, live street-level air-quality maps will be a routine public service in large cities

Prediction: by 2035, most large cities with an open-data programme will publish live, street-level air-quality maps as an ordinary public service, the way many already publish weather and transit times.

Reasoning: sensors keep getting cheaper, open-data habits are spreading, and residents increasingly expect to see the evidence behind decisions that affect their health. Projects that gather and share air-quality readings from around the world show that the technical pieces already exist.

Confidence: moderate, roughly 60 percent. The uncertainty is mostly political and organisational, not technical: someone has to maintain the sensors and explain the data.

What would prove us wrong: if by 2035 most large cities still publish only a handful of station averages, or if published maps are widely abandoned because of accuracy problems.

How to check: survey the largest 50 cities in 2035 and count how many offer live, street-level readings with documented uncertainty.