Road transport contributes a significant amount of small particles, especially in cities where transport is estimated to contribute more than 50 % of these particles. These small particles are dangerous when we breathe them, and are a leading cause of various diseases including heart attack and stroke, cancer, aggravated asthma and premature death. The World Health Organization estimated in 2012 that 7 million people die annually dues to air pollution, with half of this number – 3.7 million people - attributed to these small particles.