A major pollution-mapping program that ends September 9 has turned up startling trends in climate-warming gases and soot. The data it collected over the past five years from a National Science Foundation aircraft show the tropics periodically belch huge plumes of nitrous oxide — a potent greenhouse gas — into the upper atmosphere. Arctic measurements show that the recent record summer retreats of ice cover have allowed seas there to exhale unexpected amounts of methane, another potent greenhouse gas.

Then there’s soot. Parts of the supposedly pristine Arctic skies host dense clouds of these black carbon particles. During some flights, “We were immersed in essentially clouds of black carbon that were dense enough that you could barely see the ground,” recalls Stephen Wofsy of Harvard University, a principal investigator in the program. “It was like landing in Los Angeles — except that you were 8 kilometers above the surface of the Arctic Ocean.”