Q: Which are Calcutta’s top three pollution crossroads?

A: Behala Chowrasta, Dunlop and Tollygunge.

Q: What do they have in common?

A: High density of autos.

Q: Which is the least polluted crossroad?

A: Minto Park.

Q: What saves Minto Park?

A: No autos.

A survey by the state pollution control board (2006-07) has proved yet again that where there is a two-stroke auto, there is foul air.

The pollution control board had placed “respirable dust samplers” at a minimum height of 15 feet above the ground at 18 crossings.

Respirable particulate matter (RPM) is the killer count as it invades the deepest crevices of the lungs and causes respiratory and cardiac distress.

Behala Chowrasta is the epicentre of at least six routes with 1,500-plus autos.

Dunlop is only marginally better with four routes and 1,000-plus autos.

Tollygunge hosts seven routes and 1,500-plus autos but is saved to a certain extent by some greens.

At the other end of the scale is Minto Park, which is untouched by autos.