My understanding is that in this case talk is of the emission of certain pollutants.
Read it like like 'less gases/emission of certain pollutants'
e.g. certain pollutants are X,Y,Z.
so less of certain pollutants here will imply less amount of gases of X,Y,Z.
Here we are not talking whether fewer pollutants among set of certain pollutants are getting emitted.
Please correct me if I am wrong