My guess is that the ban will be on no more new car sales. As a result, there will instead be a huge fleet of increasingly geriatric, and thus polluting, diesel and petrol cars and trucks running around (and costing a fortune to buy) after this ban goes into effect. Of course, these cars will more than make up for the pollution that newer cars would have generated, and then some, so the net effect will be more, not less, pollution.