ROME (Reuters) - Italy’s two largest cities, Rome and Milan, adopted emergency measures on Thursday to lower air pollution levels during the Christmas season.

Ambient pollution detectors in both cities have registered high levels of micro particles dangerous to health. In some neighborhoods the levels were over the limit for more than 50 days.

Officials in Rome had already banned the most polluting, older type of vehicles from circulating in a large part of the city.

They announced on Thursday that as of Monday, all vehicles, regardless of type or age, would be allowed to circulate only on alternating days depending on the last number of their license plates, odd on one day, even on the other.

Milan was even more drastic. After restrictive measures on some vehicles in recent days were not enough, officials in the northern city announced that for three days starting on Monday, there would be a total ban on private cars in the city and its hinterland from 10 a.m. to 4 p.m. (0900-1500 GMT).

To encourage use of public transport in Rome, a single ticket would be valid for the entire day instead of for a single journey while the partial ban is in effect, officials said.