emit pollution
Cars emit???? Exhaust fumes.
What's the best verb to mean this type of pollution?

I've seen -pump out- , is it correct?

And instead of fumes can we say emissions?

Question

emit pollution
Cars emit???? Exhaust fumes.
What's the best verb to mean this type of pollution?

I've seen -pump out- , is it correct?

And instead of fumes can we say emissions?

Answer

Pump out or emit are both fine.  As you probably know, if you have a choice of a phrasal verb (pump out) or a word from a Latin root (emit), the phrasal verb will be the more informal option.

'Emissions' is more a more formal word than 'fumes' in this context.

Answer

I'm not sure if I have ever used pump out in this situation. Here are some examples of what I might say.

A hybrid car emits less exhaust than a diesel truck.
Because there are more cars in big cities, emissions levels are higher. 
This car is emitting a lot of exhaust fumes.