More than 15 years of atmospheric observations and measurements by satellites have revealed both increases and decreases in air quality, the European Space Agency reported Monday.
Nitrogen dioxide from the use of fossil fuels is a significant pollutant in the troposphere, the lowest portion of our atmosphere, researchers said.
But why increases in some areas while other areas experience decreasing levels?
"The changes observed from space can be explained by two effects: increased use of fossil fuels in evolving economies, leading to increased pollution, and improvements in technology -- like cleaner cars -- leading to reduced pollution [in developed countries]," Andreas Richter of the Institute of Environmental Physics at the University of Bremen in Germany said.
"These changes in pollution levels are surprisingly rapid, and satellites are the only way to monitor them globally."
Satellite observations of nitrogen dioxide began with the launch of the ERS-2 satellite in 1995 and are ongoing using the ESA's Envisat, NASA's Aura and the European MetOp satellites.