In 2010, outdoor air pollution contributed 3.2 million premature deaths and 76 million years of healthy life lost globally based on cardiorespiratory effects of PM2.5 (airborne particles with an aerodynamic diameter equal or smaller than 2.5 micrometer. These are also called respirable particles because they can enter the deep lung). According to a 2016 report of the World Health Organization (WHO), air quality in most of the world is showing a worsening trend; and 9 out of 10 people live in places where ambient air quality cannot meet WHO air quality guideline values.
