When atmospheric scientist Christine Wiedinmyer first went to Ghana in 2011 to investigate air pollution produced by burning different materials — from crop stubble to coal used in stoves — she noticed an unexpected potential source: burning piles of trash. Like most residents of developed nations who hadn’t traveled broadly in the developing world, the sight of smoldering rubbish piles, which contain anything from food waste to plastics to electronics, came as a surprise to Wiedinmyer, who works at the National Center for Atmospheric Research in Boulder, Colo.