Although the smog of Paris has hit headlines recently, with mayor Anne Hidalgo introducing car-free days in the capital, it is not the French city with the highest level of air pollution.
That title goes to Marseille, which has a 31.8µg/m3 concentration of fine particles - the highest in the country.
Despite its position on the coast, Marseille's two highways and large cruise terminal contribute to the low air quality. Lyon had 29.5µg/m3 and Paris had 27µg/m3 , according to the figures published in a preview by Le Parisien.
All three cities exceeded the World Health Organization's (WHO) recommended safe level.
Meanwhile, Lyon had the largest number of polluted sites with 68. These included three Seveso sites - the most dangerous in the event of a serious accident, containing large quantities of dangerous materials.
It also included the Jean Mérieux laboratory, where highly infectious viruses including Ebola and cholera are kept for research purposes and which is located just 150 metres from the Rhone river and the city centre.
Marseille had 50 sites labelled by the study as "sensitive or contaminated", including two Seveso sites, while Paris did not have any.
Another risk measured by the study was radioactive waste storage sites, most of which comes from medical and research laboratories. Paris has 36, compared to Lyon and Marseille with 14 each. However, there are no nuclear plants close to the capital.
The environmental group used data from the Institute of Health Surveillance (InVS) and the full results will be published on Wednesday in the group's Atlas of Toxic France, with 35 maps showing the most dangerous areas to help locals identify the risks in their area.