"It stinks! I smell a constant stench of smog, I cough, I feel my throat burning," said De Luca, who lives in a second floor apartment in Milan's eastern Città Studi district.

Levels of fine particulates and other pollutants in Milan rank among the highest in Europe, data from the European Union's Copernicus Atmosphere Monitoring Service and Italian environmental lobby Legambiente showed this month.

Some residents are wearing face masks outdoors to reduce exposure to the dirty air.

Roberto Lorenzutti, who used to live in Milan, says he breathes much better since he left. He had an opportunity to work remotely during the COVID-19 pandemic, and relocated to the island of Sardinia.

"In Milan you have to try and survive in this swamp for five days a week, and get yourself out for the weekend to get a breath of fresh air," he said.

Milan and surrounding cities in Italy's affluent northern region of Lombardy have responded by activating measures on Tuesday to limit the use of the most polluting vehicles during the main hours of the day.

Milan, a city of just over one million people, lies within the densely populated Po Valley, which houses almost one third of Italy's population.

The valley's 17 million inhabitants make it one of the most polluted areas in Europe, for which Italy was in 2020 found in breach of EU clear air directives by the EU Court of Justice.

The problems are caused by dense agricultural and industrial activity in the valley, amplified by its geography which traps the air, said Valentina Bosetti, professor of Environmental and Climate Change Economics at the city's Bocconi University.

In Milan, the levels of air pollutants PM2.5, PM10 and nitrogen dioxide (NO2) last year all breached the guidelines set by the World Health Organization, Legambiente noted.

The issue is a long-standing one for the area and Giorgio Maione, Lombardy regional councillor for the environment, says progress has been made, citing a 39% reduction in PM10 concentration and 45% in NO2 over the past two decades.

Milan environment councillor Elena Eva Maria Grandi, however, said that pollution levels remain very high, and asked for closer cooperation between municipal and regional authorities to evaluate emergency measures for a city that will co-host the Winter Olympics in 2026.

"We are very worried, it is evident," she said.

(Additional reporting by Emilio Parodi, Alvise Armellini and Alberto Chiumento; editing by Keith Weir and Mark Heinrich)

By Claudia Greco and Alessandro Parodi