Paris alone with its agglomeration concentrate about 90% of the regional population on a little more than 20% of the region area. The emissions of pollutants are thus concentrated there. The metropolitan area is responsible for more than 75% of the regional NOx emissions (see density of NOx emissions below), for 70% of the hydrocarbons (volatile organic compounds, VOC) and for half of the particles. In short, the NOx emissions of the Ile-de-France region represents 10% of the national ones.