[thedoc (OP)]

Dominique asked the Naked Scientists:

Incinerators (for burning trash) have got much cleaner than in the beginning thanks to filters. But what is still coming out of the chimneys? Certainly not only water vapour ? A lot of particulate matter maybe, contributing to air pollution?

Thanks
Dominique - France

What do you think?

[evan_au]

The main thing coming out of the chimney (from an energy viewpoint) is heat.

From a chemical viewpoint, the main constituents are water vapor and carbon dioxide, with unwanted gases including oxides of nitrogen and sulfur. These contribute to smog.

Incinerators use wet scrubbers and electrostatic precipitators to remove heavier components like ash from the flue. Since the unwanted gases are partially soluble, this removes much of these too.

See: https://en.wikipedia.org/wiki/Wet_scrubber#Advantages_and_disadvantages
https://en.wikipedia.org/wiki/Smog#Photochemical_smog