Concentrations of nitrogen oxides in the air in Hong Kong have consistently surpassed maximum safe levels set by the World Health Organisation in the last five years, with average roadside emissions in Central, Causeway Bay and Mong Kok nearly 2.5 times higher, according to a mid-year review by a concern group. The Clean Air Network believes the source of such persistent roadside NOx pollution is traffic congestion spurred by uncontrolled growth in the number of private cars – at least 4.6 per cent per year – in the last decade. For air measured at ambient monitoring stations, NOx levels were highest in Sham Shui Po, Kwai Chung and Tsuen Wan, all of which recorded annual average concentrations of more than 60 micrograms per cubic metre, far in excess of the WHO’s recommended level of 40. Patrick Fung Kin-wai, the group’s chief executive, said chronically high levels of pollution were posing a significant threat to public health. He urged the government to address the threat when it formulated its planning and transportation policies. “Roadside air quality has never been at a healthy level,” Fung said. “The public health impacts such as doctors visits and premature deaths need to be looked at.” The group cited data from the Hedley Environmental Index , which estimates there were 821 pollution-related premature deaths in the first half of the year. The same three stations also recorded average sulphur dioxide concentrations far higher than the citywide five-year average of 10mg, largely from shipping emissions stemming from the cargo terminal in Kwai Chung, but also because of power plants. The five-year average concentration for particulate pollution smaller than 10 microns, or PM10, was highest in Tuen Mun, Central and Western, and Kwun Tong, all of which exceeded the citywide average of 38mg. The former two also beat the city’s 25mg five-year average for PM2.5, and were joined by Kwai Chung. “Most pollution is concentrated in the western part of Hong Kong such as Kowloon West and New Territories West,” Fung said. He recommended policies that encourage behavioural changes such as electronic road pricing and low emissions streets, as well as tighter fuel requirements for ocean vessels. The group said major infrastructure development projects in the pipeline would only intensify pollution if nothing was done. The Environmental Protection Department said there had been a clear downward trend in emissions over the last five years, which showed emissions reduction measures were paying off. From 2011 to 2015, average concentrations of PM10, PM2.5, Nitrogen dioxide and sulphur dioxide at ambient air monitoring stations fell 19 per cent, 24 per cent, 8 per cent and 23 per cent respectively, while at roadside stations, a drop of 26 per cent, 21 per cent, 19 per cent and 33 per cent, was recorded.