POLLUTION levels in Central and Western rocketed last month. Unacceptable levels of nitrogen dioxide and dust particles were found in the air, according to government statistics revealed yesterday. The Environmental Protection Department continuously monitors air quality at eight stations throughout the territory. Exhaust emissions are the main source of pollution, withdiesel-engined vehicles, such as taxis, public light buses, passenger coaches, franchised buses and light and heavy-goods vehicles, being the worst offenders. According to government projections, air quality is expected to deteriorate by as mush as 50 per cent before the start of the next millennium. But the Government has said it would be at least six to 15 years before it could enforce the conversion of diesel-engined vehicles to unleaded petrol.