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Scientists examine the health risks of Hong Kong’s notorious ‘street canyons’

13 October, 2014

Cheung Chi-fai and Ernest Kao

Findings will help urban planners minimise impact of air pollution on residents

Hong Kong’s notorious “street canyons” have become the latest research subject for a group of the world’s top scientists specialising in air pollution and health.

Researchers from Britain, Canada and Hong Kong are conducting a three-dimensional air quality study in the city, which has a unique urban morphology – a dominance of high-rises and a close proximity between the population and traffic.

The study will not only map the three-dimensional movement of air pollutants, but also try to relate the pollution levels to the health of residents living at various heights in high-rises.

It will assist urban planning and building designs to minimise pollution impacts in Hong Kong and other megacities across Asia.

The street canyon effect is often cited as one of the factors in Hong Kong’s worsening air pollution. Closely built high-rises with heavy traffic in between are blamed for blocking ventilation and trapping air pollutants.

Funded by the Health Effects Institute in the US, the 30-month study will be jointly carried out by scientists from King’s College London, University of Hong Kong, the University of British Columbia and Simon Fraser University in British Columbia.

The study consists of two parts. The first, which started in March, collects spatial air pollution data from 100 selected sites across the city. The scope of the pollutants includes fine particles, as well as nitrogen oxides and black carbon.

The second part is to identify suitable canyon sampling sites to measure vertical pollution exposure. Small sensors capable of recording pollutant concentrations as well as weather data will be installed on buildings.

Dr Benjamin Barratt, of the environmental research group at King’s College London, who described Hong Kong as an ideal “urban laboratory”, said they had selected estates in different districts to represent varying characters of street canyons.

He said the first-phase vertical monitoring in Mong Kok, Jordan, Choi Hung and Sai Wan had been completed and participants from two more districts – North Point and Hung Hom – were now being recruited.

He did not want to disclose the estate names, however, as he feared it might mislead the public into thinking that they must be pollution hotspots.

He said two sets of four monitoring units had been mounted on the exteriors of the selected buildings at four height levels. Another two sets are installed inside homes to examine the extent of pollution infiltration.

“We are assessing how pollution emitted from vehicles is trapped inside street canyons, how this changes with height and how much enters the homes of residents,” he said. “Our study is primarily concerned with mapping the level of risk to public health, but these questions are also important for city planners.”

He said the study results would help planners design buildings that minimised the impact of air pollution on the health of residents.

Barratt said they would also launch a study “relating hospital records of specific diseases with patients’ home addresses, including floors”.

Dr Wong Chit-ming, associate professor at HKU’s School of Public Health, who is taking part in the study, said the research was the first and “most systematic” ever done in a city.

Wong said the results could provide more understanding about the dynamics between pollution levels and heights.

“The higher the altitude, the less the air pollution should be. But the situation might be far more complicated than that, as city layouts and wind directions have an impact, too,” he said.

A spokeswoman for the Environmental Protection Department said: ” The dispersion of air pollutants in street canyons is a complex physical phenomenon that the scientific community, including ourselves, has been trying to better understand.

“The research project of King’s College will surely help advance scientists’ understanding of this complex physical phenomenon.”

Clean Air Network chief executive Kwong Sum-yin welcomed the research project as it would provide much-needed urban pollution analysis and modelling on a more micro, rather than a macro, scale.

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