Cities across southern Europe are experiencing dangerously high levels of smog caused by a prolonged period of dry and 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 pollution.
In Bosnia and Herzegovina, protesters have taken to the streets with gas masks demanding government actions.
Environmentalists have described the situation as a smog emergency.
In Rome, diesel cars, vans and motorcycles have been banned during peak hours, while other polluting vehicles have been banned altogether.
The restrictions, which will remain in effect over the next three days, are expected to affect approximately one million vehicles.
At least nine of the 13 areas in Rome that monitor particles, a fine powder known as PM10, have registered levels this week above the legal limit, Il Messaggero of Italy reported.
Environmental groups have complained that the city council of Rome has been too slow to act on the reported results.
Milan and Turin are among the other Italian cities that took similar measures after a sharp increase in particles was recorded in other parts of the country.
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Meanwhile, there have been protests in cities and towns of Bosnia and Herzegovina.
On Wednesday, hundreds of people with respirators and masks gathered in the northern city of Tuzla to demand urgent measures to improve air quality.
In the capital, Sarajevo, government officials have held emergency meetings to discuss measures to curb pollution.
A “alarm episode” was declared over the weekend and a ban was imposed to reduce the amount of vehicles on the roads.
Local residents have also been advised to go to the mountains, where the air is cleaner, with cheap tickets available for cable cars.
More meetings will be held on Friday.
Sarajevo is among the cities with some of the worst levels of air pollution in recent days, along with the capitals of neighboring Serbia, Kosovo and Macedonia.
In Serbia, where the government held an emergency meeting on Wednesday, residents were warned to stay indoors and avoid physical activity, especially those with health conditions such as asthma.
Serbia’s Prime Minister, Ana Brnabic, blamed the high levels of contamination of domestic heating and old diesel cars.
Ms. Brnabic said that measures to address the problem would include stricter controls on vehicle emissions, improving and replacing filters in power plants and, in the long term, a tree planting program.