I refer to the letter headlined, 'Deadly', on the ultraviolet (UV) Index in Hong Kong (Sunday Morning Post, July 9).
The UV Index in Hong Kong has a long-term average of 2.8. This is calculated from data obtained by the Hong Kong Observatory since it began UV measurements on August 1, 1999.
On a typical fine and sunny day in summer, the average daily UV Index in Hong Kong is about six. On these days, the UV index may briefly reach a maximum of 12 or slightly more near noon. Our records show that since August 1, 1999, some 19 days (that is, less than six per cent of the total number of days) had a maximum UV Index of 12 or higher. The maximum UV Index in Hong Kong is comparable with those in cities elsewhere in the region or at about the same latitude as Hong Kong. For instance, Taiwan has a maximum of between about 11 and 13. The maximum in Miami, Florida, is about 11. In San Diego, California, it is also about 11.
The purpose of the Observatory's UV Index Advisory is to promote preparedness and awareness of the possible harm of prolonged over-exposure to UV radiation, and to provide information on UV radiation levels in Hong Kong. This UV Index is broadcast hourly by the electronic media, by television in the main news programmes and daily by the print media.
Your correspondent mentioned ozone depletion. For Hong Kong, there is no ground for concern. Ozone measurements obtained routinely by the Observatory since late 1993 using balloon-borne ozonesondes do not indicate a decreasing trend.