You may not have noticed, but if you've been living in a major US city for the past decade, your quality of air has actually been improving. New Images out from NASA satellites show this significant reduction in air pollution levels in a series of striking photographs released this week.

"After ten years in orbit, the Ozone Monitoring Instrument (OMI) on NASA's Aura satellite has been in orbit sufficiently long to show that people in major U.S. cities are breathing less nitrogen dioxide - a yellow-brown gas that can cause respiratory problems," the space agency reported in a recent press release.

According to NASA, Nitrogen dioxide is a common pollutant that falls under strict regulation by the United States Environmental Protection  Agency (EPA) as it is considered a significant threat to human health. Like many major air pollutants in the US, the gas comes primarily from combustion engines and coal power plants.

Remarkably, NASA points out that levels of Nitrogen Dioxide have decreased - especially along the East Coast where it was most concentrated - even while the number of cars on US roads has increased.

The difference in average pollution levels between 2005-2007 and 2009-20011 is pretty clear to see when presented visually, but NASA is quick to warn that the US isn't in the clear just yet.

"While our air quality has certainly improved over the last few decades, there is still work to do - ozone and particulate matter are still problems," said Bryan Duncan, an atmospheric scientist at NASA's Goddard Space Flight Center.

An estimated 142 million people still live in areas in the US with unhealthy levels of air pollution, the EPA reports. What's worse, only about ten percent of all urbanites in the word are currently breathing air that can meet recommended safety levels, according to the World Health Organization (WHO).

Still, It's hard not to be encouraged by this latest news. You can check out the data for yourself at NASA's Earth Right Now, and explore some interactive images here.