The view on the Eiffel Tower was once again obscured by brown smog last Wednesday as Paris and much of northern France suffered a spike in pollution.

Airparif, monitoring air quality in the greater Paris area had forecasted an index increase to 90/100 for that day and an average of 73/100 for the next day.
“The pollution levels are consistent. If we don’t go over the alert level, we won’t be far away,” said Airparif.

Authorities measure the concentration of particulates in the air with a diameter of less than 10 µm (PM10) in order to determine pollution levels. Diesel vehicles, heating and heavy industry emit this type of particles. The measurements also include a smaller class of particles, which – with less than 2.5 µm – penetrate deep into the respiratory system, enter the blood system and are a recognised cause for cancer. The safe limit for PM10 is set at 80 microgrammes per cubic metre (µg/m3).

Paris authorities have put in place certain emergency measures, such as a limitation of the top speed of 20 km/h (12 mph) on motorways in the Paris area. Additionally, Paris authorities could limit the access to the French capital to every second car and declaring public transport free of charge – like exactly one year ago. This was last implemented on 17 March 2014 during a peak level of pollution.

Meanwhile Paris has declared it will successively ban the more polluting technologies from entering the city centre. This multi-step approach culminates in the complete ban of diesel vehicles from 2020 onward. At the same time, on the other side of the Channel, London Boroughs have become active, the Borough of Islington already levying a surcharge on more polluting diesel.

According to a 2011 World Health Organisation report, the planet’s most polluted city was Ahvaz in Iran with an average of 372 µg/m3. Beijing had an average of 121 µg/m3, while Paris was measured at 38 µg/m3.

Nitrous oxides – almost more than particles – are a strong contributor to the creation of smog. In almost all larger urban areas in Europe with strong diesel market share, the main axes show dramatically increased concentrations during peak traffic.