When they are burned, diesel, kerosene, firewood, and other carbonaceous fuels produce black and brown carbon particles known as soot. Humans have used soot as a pigment since prehistoric times and still use it in tires, inks, and plastics. But soot generally is not humanity’s friend. Unregulated coal-burning led to soot-blackened buildings, like Edinburgh’s St Giles’ Cathedral in figure 1. Airborne soot particles absorb solar energy and act as condensation nuclei for cloud droplets; soot is also a pollutant that can lead to lung cancer and respiratory diseases. To help engineers design combustion systems that produce less black carbon, researchers have long wanted to better understand the process by which soot forms.
On Earth, no natural processes besides combustion produce soot. In interstellar space, similar high-temperature conditions may produce similar carbonaceous dust (see the article by Alessandra Candian, Junfeng Zhen, and Alexander G. G. M. Tielens on page 38...
