Rush hour traffic at Paris's Arc de Triomphe which is seen through a small-particle haze on 13 March 2014.

Red-alert pollution levels have prompted several French cities to make public transport and green schemes, like Paris's Velib bike-share and Autolib electric cars, free. But will the measures have any impact?

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More than 30 regions - from Brittany to the Rhône valley - are on maximum air pollution alert on Friday for the fifth consecutive day and the emergency is expected to last at least until Sunday.

Despite unseasonably warm weather in the north, people are being urged to stay inside, because of high levels of particles in the air.

In northern France, including Paris, as well as in the Rhône valley, officials are encouraging people to leave their cars at home and avoid adding pollution to the air.

Concerned about the pollution health risk, Paris authorities declared the metro and bus services free on Friday and over the weekend.

Grenoble, in the Alps, Caen and Rouen in Normandy and Reims in the east added similiar measures to regular speed limits and diversion of truck traffic from the city.

But French environmental groups are worried over the recurring spikes in air pollution and have resorted to filing a lawsuit on Tuesday.

They want a judicial investigation into who should be held responsible for pollution “endangering the lives of others”.

Sebastien Vray of the NGO Respire (Breathe), which is one of the plaintiffs in the lawsuit, says it won’t be easy to find out exactly who is to blame but the lawsuit is also to try to make people take pollution more seriously.

It is not known how much impact free transport will have on pollution, according to the Pierre Serne, a representative of the Green party, EELV, on the regional transport authority, Stif.

He would have preferred alternating road use according to registration numbers, he told Le Parisien newspaper, claiming that it would reduce traffic by 50 per cent.

Officials are reluctant to enact such a measure because of the economic implications for the Paris region.

Alternate traffic circulation is part of one emergency measure that should be studied this year, according the environment ministry.

It was put into effect in October 1997 in the Paris region and caused a 20 per cent drop in traffic drop and a 22 per cent drop in atmospheric carbon emissions, the ministry says.

In December 2013 an inter-ministerial comittee on air quality (CIQA), suggested 38 measures to tackle pollution.

Nineteen of the 38 are already in operation or are on the way to being implemented.

Compensation for using a bike to go to work is one measure being investigated and CIQA recommends the use of coloured stickers to identify the level of atmospheric pollution of each car.

Such a plan is already in operation in Germany, Italy and Great Britain.

France has a poor record on anti-pollution policy compared to many European countries and is struggling to implement EU standards.

The country could face fines of 240,000 euros a day for non compliance with European norms, partly because of a long-established policy of low tax on highly polluting diesel fuel.

In France 42,000 people die prematurely due to fine particles and others develop chronic diseases such as asthma.

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