India, Oct. 20 -- Every winter, India learns to read the air through numbers. AQI readings dominate headlines, schools consider closures, and families check pollution apps before stepping outside. When the smog lifts and the numbers improve, attention moves elsewhere.

But the need for safer air does not end when the skyline becomes visible again.

India needs to approach air as a year-round public-health priority. That means sustaining efforts to reduce outdoor pollution while paying far greater attention to the air inside our homes, schools, workplaces and hospitals.

The Air Quality Index has helped make an invisible problem visible. It gives citizens a useful warning and governments a basis for action. Yet an outdoor AQI reading canno...