Faced with air pollution levels that on some days force the elderly and the asthmatic to stay indoors and have some foreigners contemplating a move to cleaner climes, the government of this financial city said that it was time to get tough on the worst polluters. Donald Tsang, the Hong Kong chief executive, outlines an anit-pollution agenda in an annual policy address that the promised some carrots and threat of big sticks to get industry and the polluting public to help clean up the city's frequnelty murky skies.