Satellite measurements show that nitrogen dioxide in the lower atmosphere over parts of Europe and the US has fallen over the past decade. More than 15 years of atmospheric observations have revealed trends in air quality.

As the world's population increases, economies in many countries are also growing and populations are concentrating in large cities. With the use of fossil fuels still on the rise, pollution in large cities is also increasing.

Nitrogen dioxide is an important pollutant in the troposphere, the lowest portion of our atmosphere.