Toxic particulate dust levels have exceeded the maximum allowed by European standards for more than two weeks, often by a factor of two, ANSA reported Friday.
City officials have said the traffic ban will be implemented if levels exceed the limit for 18 consecutive days.
Levels were 105 micrograms per cubic meter in Milan Friday; European Union standards dictate a maximum level of 50 micrograms per cubic meter on any given day.
Milan and other cities in Italy's northern plain, such as Turin, Bergamo and Brescia, experience some of the worst air pollution in Europe, an Italian government survey found.
Milan ranked 218 out of 221 European cities in terms of air quality for the years 2004 to 2008, the survey said.