Air pollution deteriorated in urban areas last year, exceeding limits for toxic pollutants, according to figures released yesterday. The annual report to the Advisory Council on the environment showed worsening air quality, mostly as a result of exhaust from diesel vehicles. Particulates from diesel vehicles have been linked to diseases such as asthma. The report showed particulate levels for the year remained high, ranging from 50 micrograms per cubic metre to 75. Six monitoring stations recorded at least one violation of air quality objectives for particulate levels. Ozone levels breached more short-term air quality objectives, violating the hourly limit four times at Kwai Chung and five times in Central and Western. Nitrogen dioxide 24-hour levels were exceeded twice at Shamshuipo and three times at Mongkok in 1996. Council chairman Peter Wong Hong-yuen said the results made depressing reading. The council recommended the Environmental Protection Department simplify the daily air quality index to make it more meaningful for the public.