Cities across southern Europe are experiencing dangerously high levels of smog caused by a prolonged period of dry sunny weather and light winds.
Temporary bans on diesel vehicles have been ordered in major Italian cities, including the capital, Rome, in an effort to reduce the pollution.
In Bosnia-Herzegovina, protesters have taken to the streets in gas masks demanding action from the government.
Environmentalists have described the situation as a smog emergency.
In Serbia, where the government held an emergency meeting on Wednesday, residents were warned to remain indoors and avoid physical activity – especially those with health conditions such as asthma.
Serbia’s Prime Minister Ana Brnabic blamed household heating and older diesel cars for the high pollution levels.
Ms Brnabic said measures to tackle the issue would include more and stricter checks on vehicle emissions, improving and replacing filters on power stations and in the longer term, a programme of tree-planting.
In Rome, diesel cars, vans and motorbikes have been banned during peak times, while other polluting vehicles have been banned altogether.
Further north, where air pollution is typically worse, Milan, Turin and Bologna are among other cities to take similar action after recording a sharp rise in particulate matter.
Italy’s permitted limit for PM10 particles is 50 micrograms per cubic metre, but in recent days that limit has been exceeded – especially in the north, where monitoring stations near Bologna show levels as high as 125 micrograms per cubic metre.
A high concentration of PM10 and PM2.5 particles can pose significant health risks because they are small enough to penetrate deep into the lungs. The most common source is vehicle engine emissions.
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