Visibility across Victoria Harbour last year was the worst on record. Releasing a study on visibility yesterday, the Hong Kong Observatory said the world-renowned vista was blurred by air pollution on almost one in six days in 2004. Visibility was less than 8km about 18 per cent of the time, equivalent to 1,577 hours. This was 40 per cent longer than in 2003 and about 10 times worse than in 1968. Visibility is rapidly deteriorating, worsening at a rate of 5.7 per cent per decade starting in 1986, compared with 0.77 per cent between 1968 and 1986. This trend was also coupled with a worrying finding that wind velocity recorded at the observatory decreased by 1.69km/h during the past decade, hampering the dispersal of pollutants. The decline is possibly related to increasing urban development. The study comes amid mounting concerns over pollution in the Pearl River Delta, which has led to a decline in air quality and visibility across the region. During the worst case of air quality last year, the Two IFC could barely be seen from the Causeway Bay shoreline in September. The observatory said last year saw an across-the-board deterioration in visibility regardless of the season, with new records in February, April, June, August, September, October and December. Yeung Kai-hing, assistant director of the observatory, said deteriorating visibility was a regional problem resulting from emissions from power plants, vehicles and factories. 'The problem has to be addressed at the emission source, but we do not expect there will be significant relief in the short term,' Mr Yeung said.