Stuttgart called on residents to leave their cars at home indefinitely as of Monday, in a bid to reduce levels of fine particulate matter in the air that have repeatedly exceeded European Union safe limits.

The southwestern city, whose location in a basin leads to higher concentrations of air pollutants, is the most polluted in Germany, and levels of the harmful particulate matter have long been well above the 50 micrograms per cubic liter imposed as a limit by the EU.

Currently, city authorities are requesting commuters to travel by public transport or car-sharing on a voluntary basis, but officials say non-compliance may be subject to fines in the future if air pollution does not come down.

Stuttgart's mayor, Fritz Kuhn, who belongs to the environmentalist Green party, said the alarm had so far not had any great effect on traffic in the city. But he said he trusted residents' sense of responsibility, asking them to leave their cars at home.

First-ever alert

It is the first time a large German city has had a pollution alert of this kind. Fine particulate matter is harmful to health and a long-term carcinogen.

Air pollution is a major factor in respiratory diseases

It is unclear how long the voluntary measure in Stuttgart will last, but the German meteorogical service says it may take a week for levels to be reduced.

Stuttgart residents and environmentalists have protested at the voluntary nature of the request. They argue that a better solution would be to ban by law the diesel vehicles, which are the main cause of the pollution.

Mayor Kuhn, however, defended the voluntary nature of the measure, saying he thought it was generally better for society to find solutions of its own accord.

Stuttgart is often referred to as "car city," with carmakers Daimler and Porsche both headquartered there.

tj/rc (dpa, AFP)