Story highlights Nitrogen dioxide is a major pollutant that can play a role in asthma and other respiratory illnesses

New NASA maps show increases in China and decreases in U.S. and western Europe

(CNN) The United States and Europe are among the world's largest emitters of nitrogen dioxide -- but both have also shown the most dramatic reductions in these emissions between 2005 and 2014, according to new global NASA satellite maps.

Nitrogen dioxide is a yellow-brown gas that is a common emission from cars and industrial activity. It is a major respiratory pollutant in urban smog.

Photos: NASA satellite images show changes in global air quality Photos: NASA satellite images show changes in global air quality This global map shows the average concentration of nitrogen dioxide in the atmosphere in 2005, as detected by the Ozone Monitoring Instrument aboard the Aura satellite. Blue indicates an observed decrease in nitrogen dioxide, and orange indicates an observed increase. Hide Caption 1 of 13 Photos: NASA satellite images show changes in global air quality This map shows the average concentration of nitrogen dioxide in the troposphere (the atmospheric layer closest to the surface of Earth) in 2014. Hide Caption 2 of 13 Photos: NASA satellite images show changes in global air quality Average nitrogen dioxide concentrations across the U.S. in 2005. The U.S. and Europe are among the largest emitters of nitrogen dioxide. Both regions also showed the most dramatic reductions between 2005 and 2014. Hide Caption 3 of 13 Photos: NASA satellite images show changes in global air quality Average nitrogen dioxide concentrations across the U.S. in 2014. Hide Caption 4 of 13 Photos: NASA satellite images show changes in global air quality This trend map of the U.S. shows large decreases in nitrogen dioxide concentrations, between 20-50%, from 2005 to 2014. Only decreases are highlighted here. Hide Caption 5 of 13 Photos: NASA satellite images show changes in global air quality This trend map of Europe shows the change in nitrogen dioxide concentrations from 2005 to 2014. Nitrogen dioxide has decreased by as much as 50% in western Europe. Hide Caption 6 of 13 Photos: NASA satellite images show changes in global air quality



In the Middle East, researchers suggest that the increased nitrogen dioxide levels since 2005 in Iraq, Kuwait and Iran were down to economic growth in these countries. But in Syria, the decrease since 2011 is most likely because of the civil war which began in that year, and has since left The trend map of the Middle East shows the changes in nitrogen dioxide concentrations from 2005 to 2014.In the Middle East, researchers suggest that the increased nitrogen dioxide levels since 2005 in Iraq, Kuwait and Iran were down to economic growth in these countries. But in Syria, the decrease since 2011 is most likely because of the civil war which began in that year, and has since left more than 300,000 people dead and forced 10.6 million -- nearly half the population -- to flee. Hide Caption 7 of 13 Photos: NASA satellite images show changes in global air quality The trend map of the Persian Gulf shows the change in nitrogen dioxide concentrations from 2005 to 2014. Hide Caption 8 of 13 Photos: NASA satellite images show changes in global air quality The trend map of South Africa shows the changes in nitrogen dioxide concentrations from 2005 to 2014. The South African region encompassing Johannesburg and Pretoria has the highest nitrogen dioxide levels in the southern hemisphere, but the map shows a complex situation playing out between the two cities and neighboring power plants and industrial areas, say the researchers. Hide Caption 9 of 13 Photos: NASA satellite images show changes in global air quality Average nitrogen dioxide concentrations in South Africa in 2014. According to the researchers, the Johannesburg-Pretoria metro area saw decreases after new cars were required in 2008 to have better emissions controls. The heavily industrialized area just east of the cities, however, shows both decreases and increases.



The decreases may be associated with fewer emissions from eight large power plants east of the cities since the decrease occurs over their locations. However, emissions increases occur from various other mining and industrial activities to the south and further east. Hide Caption 10 of 13 Photos: NASA satellite images show changes in global air quality The trend map of East Asia shows the changes in nitrogen dioxide concentrations from 2005 to 2014. China, the world's growing manufacturing hub, saw an increase of between 20-50% in nitrogen dioxide, much of it occurring over the North China Plain.

Three major Chinese metropolitan areas -- Beijing, Shanghai, and the Pearl River Delta -- saw nitrogen dioxide reductions of as much as 40%. Hide Caption 11 of 13 Photos: NASA satellite images show changes in global air quality The trend map for Texas shows the percentage change in nitrogen dioxide concentrations from 2005 to 2014. Hide Caption 12 of 13 Photos: NASA satellite images show changes in global air quality This trend map for North Dakota shows the percent change in nitrogen dioxide concentrations from 2005 to 2014. To see the data in full, visit the NASA website. Hide Caption 13 of 13

The latest images show how pollution levels have changed in the last decade in various regions and 195 cities across the world. But the space agency has gone a step further and looked at how factors on the ground, such as large power plants, have impacted the findings.

China, the world's growing manufacturing hub, saw an increase of between 20-50% in nitrogen dioxide much of it occurring over the North China Plain, a densely populated area that runs from Beijing south to Nanjing.

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