I beg to differ. He said the data showed that between 2010 and 2015, the concentrations of different pollutants in Central decreased. However, studying the level of nitrogen dioxide, an important indicator of roadside air pollution, we found that 2013, 2011 and 2010 actually recorded the highest readings of nitrogen dioxide respectively since 1998. To take a 10-year review, we would see that in 2006, the annual average concentration of nitrogen dioxide in Central was 96µmicrograms per cubic metre; whereas in 2015, it was 93µmicrograms per cubic metre. Strictly speaking, there was little improvement for a whole decade.

A main factor contributing to the high level of nitrogen dioxide is traffic congestion. From 2003 to 2013, the number of vehicles increased by 30 per cent from 524,000 to 681,000. During the same period, the average car journey speed in urban areas dropped by about 11 per cent from 25.6km/h to 22.7km/h. In some road sections in Central during morning peak hours, the average car journey speeds even dropped to 12km/h! Although measures such as the replacement of old diesel vehicles and the retrofitting of selective catalytic converters for LPG vehicles helped alleviate the pollution problem, the uncurbed growth of private cars rendered attempts to clean up roadside air impossible.