I've always held a view that banning innovations, such as diesel engines, isn't a solution to environment problems (if there are any). In my district where I live, we have planted or self grown cover of 30% land to tree ratio. And we actually inhale the best of air. The cities anywhere should understand the real problem which is deforestation. It can easily be overcome by planting enough trees wherever possible. Why don't they focus on tree planting instead of banning this or that?