Many people worry about air pollution from motor vehicles, with good reason. Yet, marine vessels are also significant, although lesser known, sources of toxic emissions into the air. The boom in international trade with China has made ports in Hong Kong and the Pearl River Delta the busiest in the world. Increased activities by ships, trucks, trains, cargo cranes and harbour craft in the region mean they can no longer be ignored as pollution sources. This is especially troubling given their proximity to highly populated city centres. The think-tank Civic Exchange has provided a valuable public service by providing a study on this growing problem, along with practical recommendations that authorities would do well to take seriously. Hong Kong and the delta region have lagged behind the best practices in North America and Europe, the study finds. However, many local operators are taking initiatives, on their own, to make their operations more energy-efficient and friendlier to the environment. The Hong Kong government and Beijing have also ratified a key annex to the International Convention for the Prevention of Marine Pollution from Ships. In Hong Kong's case, it came into effect at the start of this month. Still, much work needs to be done. New rules and regulations - such as emission standards - need to be brought in line with the annex provisions and local needs. For this to happen, the Hong Kong government and authorities in Guangdong must take the initiative. Many port operators, according to the report, complain that some of their smaller rivals are enjoying a free ride from their anti-pollution programmes without having to take part in them. Only regulations can create a level playing field where everyone is bound by the same rules. Most of these rules and standards are not difficult to formulate or enforce. Civic Exchange recommends use of low-sulfur fuels, reducing vessel speed limits in delta waters, and educating port staff. But they need cross-border standards and co-operation to work. Clearly, our ports will only become busier as the mainland's economic growth continues. For the sake of public health, we have a duty to make our ports clean and green.