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.
The requirements focus on prescriptive design specifications, such as providing setbacks on narrow streets, and increasing the spacing between towers. But these are not necessarily effective; for example, set-back buildings are only helpful on streets parallel to prevailing winds. Meanwhile, air ventilation assessments that measure whether designs are actually effective at improving air flow are still conducted on a voluntary basis only.
Furthermore, the new guidelines cannot be enforced on building projects that require neither Town Planning Board approval nor land lease modification. In those cases, developers need only follow the requirements if they wish to claim additional gross floor area for other green building features.
These incentives are not attractive enough to encourage participation. It would be more effective to require air ventilation assessments with performance targets for all new developments, and instead of prescribing designs, the government should allow architects the freedom to solve problems creatively.
In sum, bolder measures are required to make Hong Kong's urban environment a better place to breathe.
Carine Lai is a project manager at Civic ExchangeTopics: Hong Kong air pollution Roadside pollution Urban Planning Environment