Brick-making factories surrounding Bangladesh's capital have turned Dhaka into a toxic trap. But a new project to build more eco-friendly factories might help clear the air.

The UN and the Asian Development Bank are using $72m of aid money from Japan and European countries for a project that makes the production of bricks much cleaner.

With the new technology, bricks are made underground and the carbon dioxide stays there. Some of those new factories produce more than 70,000 bricks every day, at a cheaper price and in a more environmentally friendly way.

But some in the country remain sceptical about the new technology.

Bangladesh is among the lowest carbon emitters in the world, and donors to this project are some of the world's major polluting countries.They can claim the amount of carbon dioxide emission saved in Bangladesh as their own as part of what is known as carbon trading.

Al Jazeera's Nicolas Haque reports from Dhaka.