Geneva makes public transport temporarily free to combat pollution spike

Geneva, in the western French-speaking part of Switzerland, is experiencing a severe peak of ozone pollution - a harmful gas that can cause problems breathing and can trigger headaches and asthma attacks, according to the World Health Organization.

The city's anti-smog system showed that ozone concentrations had exceeded an environmental health safety threshold of 180 micrograms per cubic meter over 24 hours, according to a statement by the Canton of Geneva.

On Tuesday, temperatures hit 37 degrees Celsius (98.6 Fahrenheit) with the government issuing heat warnings for western and southern parts of Switzerland.

High temperatures and low cloud cover mean ozone pollutants accumulate and take longer to be dispersed, the Environment Office for the Canton of Geneva told Reuters.

In response, public transport was made free for the first time on Wednesday throughout the canton, to encourage residents and visitors to switch from their cars to buses, trams, trains and boats, in order to reduce traffic emissions.

"The measures taken under this emergency protocol aim to reduce emissions of nitrogen oxide, notably by promoting public transport and limiting the circulation of the most polluting vehicles," the environment office said.

Passengers will not require a ticket, and ticket checks will be suspended until the pollution improves, authorities said in a statement.

Between 6 a.m. (0400 GMT) and 10 p.m., only lower-emitting cars are allowed to circulate within the centre of the city.