Geographically, Hong Kong is part of the Pearl River Delta. As pollution generated on one side of the Shenzhen River impacts the other, local initiatives to clean up the environment can never be fully successful unless backed by regional efforts. The Hong Kong Observatory recently confirmed what has long been obvious to all - visibility in Hong Kong is now four times worse than it was 30 years ago. In fact, worsening air pollution does not just affect Hong Kong. The region as a whole is now shrouded in haze, if not smog, on most days. Hong Kong and Guangdong used to indirectly point accusing fingers at each other for causing the problem. Guangdong admitted its old coal-fired power plants were spilling out thick, black smoke and its vehicle exhausts were rich in carbon, sulphur and lead. But it also noted that pollutants from Hong Kong could be blown northward to affect the province - a point accepted by Hong Kong only in recent years. Now that both sides have put aside that dispute and research has pinpointed the sources of pollution, it is gratifying that Guangdong has shown a clear determination to work closely with the SAR to address the problem. Over the next few days, Guangdong is expected to adopt much more stringent standards on emission and fuel. Some old coal-fired power plants may even be closed. The measures will not immediately clear the sky, but they are a good start. In fact, there is only so much Guangdong can do. The province alone cannot decree that refineries on the mainland produce cleaner diesel. Even after it has adopted stricter standards, vehicles from provinces using sub-standard fuel will still cause problems as they pass through Guangdong. The province's efforts to combat water pollution is no less daunting. Just cleaning up the tributaries of the Pearl River is a herculean undertaking. Although the problem does not directly affect Hong Kong, this is an area where the SAR's expertise may prove helpful. Hong Kong had a head start over Guangdong in addressing the sewage problem. In the late 1980s, it banned the discharge of animal waste and untreated sewage into rivers and storm water drains. Regrettably, these measures pushed some of the most polluting factories across the border. Guangdong has 'benefited' from their relocation, and it is time it cleaned up the smudge.