In an unprecedented compilation of air quality data released by the World Health Organization (WHO), air pollution is reaching levels that threaten people’s health. WHO amassed data from 1100 cities across 91 countries, including capital cities and cities with more than 100,000 residents. WHO estimates that 2 million people die each year from breathing in tiny particles present in indoor and outdoor air pollution. The particles are called PM10, which are particles of 10 micrometers or less which can penetrate into the lungs and can cause heart disease, lung cancer, asthma, and acute lower respiratory infections. Current air quality standards call for a PM10 of 20 micrograms per cubic meter as an annual exposure average. The new WHO data shows that the average PM10 is some cities has reached up to 300 micrograms. The worst air quality found in the world today is in India, Pakistan, Iran, China, and Africa. The best air quality is found in Canada and the U.S. according to WHO. The largest contributors to urban outdoor pollution arises from automobiles, small manufacturing, the burning of biomass and coal fired power plants. Residential wood burning is also a contributor during colder months. Even though U.S. air quality rated higher than the rest of the world, there still is a long way to go to improve it further. Just ask anyone who lives in a major U.S. city if the air quality on a hot summer day couldn’t be improved.