NO2 exposure levels (left) and deaths attributable to NO2 (right) in cities with a population of 50,000 or more in 2019. NO2 levels are high in cities across all regions and income levels, while death rates are highest in Asia and Eastern Europe. 

Population-weighted annual average pollutant concentrations and associated health burden in cities, in 2019.

About NO2

Nitrogen dioxide (NO2) is a pollutant generated mainly through the burning of fuels in vehicles, power plants, and industrial facilities.

As a major component of vehicle exhaust, NO2 is often used as a proxy for tracking traffic-related air pollution and related health effects. NO2 and other nitrogen oxides also contribute to the formation of other harmful pollutants like ozone and PM2.5.  

NO2 irritates the airways. It is linked with more frequent and severe asthma symptoms and may increase a child’s likelihood of developing asthma. NO2 exposure may also impair lung development in children, intensify allergies, and make people more susceptible to respiratory infections.


Woman wearing mask


Why it Matters

Most cities have unhealthy levels of NO2 pollution. As of 2019, 94% of the 2.6 billion people who live in cities with a population of 50,000 or higher were exposed to NO2 levels that exceeded the World Health Organization (WHO) guideline of 10 µg/m3.

People who live, work, or go to school closer to roadways often experience the heaviest traffic pollution exposure. People with asthma or other health problems that are caused or exacerbated by NO2 pollution can get sick more often, require more health care, and miss work, school, or family obligations. This creates a burden on the affected individuals as well as their families and, more broadly, society and the economy.

women riding bikes


Most cities still have too much NO2 pollution, but trends are heading in an encouraging direction. Between the years 2010 and 2019, more than 200 additional cities met WHO’s  NO2 guideline. Of the 20 cities with the largest drop in NO2 exposure between 2010 to 2019, 18 are located in China. The other two are Los Angeles, United States and Tokyo, Japan.

Many cities have implemented measures to reduce traffic- related air pollution. For instance, London’s Ultra Low Emission Zone initiative delivered a 36% reduction in NO2 in the first six months after its launch in 2019. Traffic measures like this have yielded air quality improvements in other cities as well.