*I can't understand why the writer used -ing form of verb in my example after conjunctive adverb "therefore".*

*However, I know that 'therefore', 'however', 'hence', 'nevertheless', .. are conjunctive adverbs. They have to connects two independent clauses.*

I am still confused why we use 'ing' form after adverbs, because we often use 'ing' form after prepositions not adverbs.

> "They could also impose ‘green taxes’ on drivers and airline
> companies. In this way, people would be encouraged to use public
> transport and (they would be encourage) to take fewer flights abroad,
> therefore reducing emissions."

 Thanks.