Mayor Sadiq Khan’s Londonwide expansion of the ultra-low emission zone (Ulez) resulted in a “better than expected” reduction in toxic exhaust emissions from cars and vans, a City Hall report has suggested.This helped to reduce the amount of nitrogen dioxide (NO2), a toxic gas, detected at the roadside in outer London by an estimated 2.7 per cent to 4.4 per cent – up to double that predicted.