India, Jan. 20 -- On severe pollution days in Delhi, frustration feels universal. Governments may feel they have acted, but the results appear evasive. Scientists understand the problem, but recognise the limits of intervention. Regulators confront enforcement gaps in a system shaped as much by chemistry and weather as by policy. Citizens endure air that remains punishing despite years of action. Across institutions and society, emotion converges on disappointment, tempered by the belief that progress will eventually arrive.

That dissonance reflects a familiar trajectory in air-quality management, when visible pollutants give way to invisible ones. For much of the past decade, Delhi focused, correctly, on what was overwhelming and measur...