How Camfil is preventing street level pollution by removing nitrogen dioxide in Hong Kong tunnel  

World’s largest air purification system in a tunnel with an aim to reduce carbon dioxide emissions by 11,000 tons annually

According to the United Nations Environment Programme, 92 percent of people in the Asia-Pacific region are exposed to a high level of air pollution that poses a significant risk to health. 

Highways Department in Hong Kong came up with an incredible solution to alleviate traffic congestion and tackle the serious problem of air pollution. The Central-Wan Chai Bypass is a 4.5 km link road, comprising of a flyover and a 3.7 km tunnel section that has air purification systems capable of removing at least 80 percent of key pollutants from roadside emissions. In Hong Kong, it is the first air purification system in a tunnel and the largest in the world in terms of air volume handled that removes harmful particulates, nitrogen dioxide, and other key roadside pollutants. 

What role did Camfil play in the project? 

The tunnel can handle 5.4 million cubic meters of vehicle exhaust per hour and large tunnel exhaust passes air to three ventilation buildings along the tunnel section of the project. The first step to air purification is separating respirable suspended particulates through electrostatic precipitators. Next, the air passes through the denitrification filter which is using activated carbon to remove nitrogen dioxide. Lastly, purified air is discharged into the adjacent atmosphere to prevent street-level pollution.  

Camfil provided 860 tons of activated carbon for the denitrification filter. The carbon was tested in our innovative advanced research lab in The Tech Center located in Trosa, Sweden. Camfil is adept in testing the performance of molecular air cleaning media and devices for ventilation applications and uses the global standard test method described in ISO10121. To support our global activities, Camfil operates a second ISO10121 test laboratory in Malaysia.  

Activated carbon is a powerful and extremely resourceful adsorbent and is used in many molecular air purification solutions. A specific activated carbon can be selected to target odors, irritants and toxic gases, such as volatile organic compounds (VOC), nitrogen dioxide and ozone.  
Effective results for Hong Kong’s Highway Department 

As per Kevin Lo, Highways Department Hong Kong, “The Central-Wan Chai Bypass tunnel can reduce carbon dioxide emission up to 11,000 tons annually as it cuts the journey time to five minutes which was previously reported as 30 minutes. It will take 480,000 trees to absorb this level of carbon dioxide emission from the environment."

“Camfil is proud to have been involved in this landmark infrastructure project. The tunnel is easing congestion, making travel more efficient for thousands of motorists every day and reducing the carbon footprint. Camfil, in their state-of-the-art molecular filtration laboratory, evaluated and proved the ability of a filtration media to remove nitrogen dioxide. This thorough study included tests at a range of temperature and humidity conditions, to ensure filter efficiency under all seasonal conditions experienced in Hong Kong. The tests were conducted in accordance with the global test standard ISO10121.  Our contribution to the Central Wan Chai Bypass tunnel is protecting the health of local residents at street level and in high-rise buildings near the tunnel exhaust points.” – Dr. Chris Ecob, Global Applications and Solutions Director, Molecular Contamination Control Division at Camfil 

Road Ahead

Camfil’s molecular air filters hold great potential as apart from purifying the air from hazardous gases and odors, molecular filters can be made from different sustainable raw materials, in different qualities, shapes, and sizes. Our innovative design and strong research and development allow us to conserve more, use less and find better ways so that purifying air becomes easier and better.

clean air with new link

“Every hour it can handle 5.4 million cubic meters of vehicle exhaust and reduce 80% of the respirable suspended particulates and nitrogen dioxide from the tunnel exhaust,” says Highways Department Project Manager/Major Works Kelvin Lo.


Created Thursday, April 16, 2020
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