WASHINGTON: NASA is launching an airborne mission that will map the contours of the Earth's atmosphere to discover how much pollution exists in the most remote corners of the planet and assess how the environment has changed as a result. Pollutants emitted to the atmosphere - soot, hydrocarbons, nitrogen oxides - are dispersed over the whole globe, but remote regions are cleaner, by factors of 1000 or more, than areas near the continents, researchers said. The AtmosphericTomography (ATom) mission is the first to survey the atmosphere over the oceans. Scientists aboard NASA's DC-8 flying laboratory will journey from the North Pole south over the Pacific Ocean to New Zealand and then across to the tip of South America and north up the Atlantic Ocean to Greenland. We've had many airborne measurements of the atmosphere over land, where most pollutants are emitted, but land is only a small fraction of the planet," said Michael Prather, an atmospheric scientist and ATom's deputy project scientist at University of California Irvine. "The oceans are where a lot of chemical reactions take place, and some of the least well understood parts are hard to get to because they are so remote," Prather said.