In parts of India, it is not uncommon to see people wearing a mask over their nose and mouth. The capital, New Delhi, has some of the world's dirtiest air. The pollution was a call for action for researchers at the Indian Institute of Technology Delhi. A team from that university has developed an alternative method to help people guard against heavy air pollution. The researchers invented a small respiratory filter that is placed in the nose. The device is designed to stop most dust and air pollutants from entering the body without restricting breathing. On its website, America’s Environmental Protection Agency defines particulate matter as a mixture of solid particles and liquid droplets found in the air.