Urban planners must do more to give us some breathing space
Carine Lai says our clean-air plan does not go far enough to address the city's problems of dense buildings, lack of greenery and too many cars
While recent proposals by the Environment Bureau to control vehicles' exhaust fumes have received much attention, it is also worth highlighting the role urban planning can play in reducing roadside air pollution. The "street canyon effect" can be reduced by improving ventilation, cutting vehicle use, reducing pedestrian exposure and mitigating pollutants.
The bureau's master plan to improve our air quality mentions three urban planning policies: urban greening, pedestrian schemes and cycling networks. Yet, on closer examination, these policies are missing some key elements and are unlikely to have a major impact.
First, urban greening does mitigate air pollution as vegetation absorbs pollutants. European studies, for example, have found that tree planting can reduce PM10 particles. But this requires substantial tree coverage to be effective (about 25 per cent of urban land for a 2-10 per cent reduction). Unfortunately, the greening initiatives suggested by the Hong Kong plan will not be on this scale, given the lack of space and the limited scope of the programmes themselves.
Second, keeping vehicles away from popular shopping streets reduces people's exposure to fumes and would be very beneficial if carried out ambitiously. However, pedestrianisation efforts have stalled since the early 2000s, and the master plan cautiously notes the daunting reality in Hong Kong of "limited road space and many competing needs".
Third, cycling is undoubtedly a green mode of transport. However, the government believes that safe cycling is feasible only in less densely built-up areas, so its plans for expanding cycling networks focus on the new towns and new development areas where roadside air pollution is less severe. Therefore, the benefits will not be felt in the most polluted areas.
Besides, noticeably missing from the plan are ventilation flow requirements for buildings. Despite the adoption in 2011 of new sustainable building requirements by the departments of buildings, lands and planning, there is much room for improvement.