Particulate air pollution from incomplete combustion is affecting climate over East Asia more than carbon dioxide and cause premature deaths of over half a million annually in China alone, yet its sources have been poorly understood. Scientists have now used a powerful carbon-14 method to show that four-fifths of the soot particle air pollution are from fossil fuel combustion such as household cooking with coal briquettes and city traffic, drastically changing the view on sources and guiding efforts to mitigate emissions.