Most cities have polluted air, but the type of pollution varies from place to place.
It’s a simple fact: Most urban residents around the world are breathing unhealthy levels of pollution. While there are many forms of air pollution, two main pollutants are particularly important in urban environments: ambient (outdoor) fine particle air pollution (PM2.5) and nitrogen dioxide (NO2).
Ambient PM2.5 comes from vehicle emissions, coal-burning power plants, industrial emissions, and other sources. Because of their size – 2.5 micrograms or smaller – these tiny particles can easily get into the lungs, and in some cases, the bloodstream and impact our health in various ways. Nitrogen dioxide comes from many of these same sources, with vehicle traffic being a main source of NO2 in urban areas.
Research suggests NO2 exposure is not only linked to aggravation of asthma symptoms but is also linked to the development of asthma in children.
Comparing levels of these pollutants in cities around the world reveals strikingly different geographic patterns. PM2.5 pollution tends to be highest in low- and middle-income countries, whereas NO2 levels are high across countries of all income levels.