New Delhi's air quality is consistently ranked among the world's worst. But a perfect storm of problems is exacerbating the problem to potentially deadly levels. Farmers who have recently harvested crops in neighboring states are illegally burning their fields, sending smoke into the air. Construction projects and pollution from vehicles in a city that lacks adequate public transportation are making things worse.

This week, the smog was 10 times worse than reigning pollution champion Beijing, where air-quality problems have reached Olympic proportions. Some parts of New Delhi have pollution 40 times the World Health Organization-recommended safe level.

People huddled indoors with expensive air purifiers, indoor plants and closed windows.

But doctors say it won't be enough to prevent some deaths in the city of 20 million people. Children are the most vulnerable.