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Nitrogen dioxide is a gas emitted during the combustion of  fossil fuels.

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It's released from the tailpipes of cars, and the smokestacks

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of power plants. Together, these emissions affect the quality 

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of the air we breathe. Since 2004, an instrument aboard NASA's AURA 

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satellite has measured levels of nitrogen dioxide in Earth's atmosphere.

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In 2014, we released satellite images that show how 

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environmental regulations have led to reductions in nitrogen dioxide 

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over major U.S. cities. Now, we've created a global maps

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that allow us see how levels have changed around the world over the last decade.

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In Western Europe, despite the recent vehicle emissions scandal 

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nitrogen dioxide levels have decreased by as much as 50 percent

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due to tighter environmental controls. In China, we see an increase

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in levels over most of the country due to a rise in coal use for power generation 

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but decreases for some cities, like Beijing, where a growing

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 middle class is now demanding cleaner air. In the Middle East, we see 

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decreases in nitrogen dioxide levels over Syria due to the country's

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civil war and displacement of its population. Meanwhile, levels have

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gone up in neighboring countries where millions of Syrians have taken refuge. 

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In the U.S., the only increases are in regions with intensive

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oil and natural gas extraction, including fracking. In North Dakota 

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and Texas, we see increases of 30% in some areas.

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By monitoring levels of nitrogen dioxide from space 

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we can see and quantify the effects of things like energy usage 

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environmental policy and even civil unrest on

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air quality across the globe.