Ice sheets, deserts, rivers, islands, coasts and oceans — the features of Earth's surface are wildly different, spread across a vast geography. The same is true for Earth's thin film of atmosphere and the mix of gases it holds, although the details are invisible to human eyes. 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. A new NASA airborne campaign aims to map the contours of the atmosphere as carefully as explorers once traced the land and oceans below.The Atmospheric Tomography, or 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. ATom will discover how much pollution survives to the most remote corners of the earth and assess how the environment has changed as a result.