As a short-lived climate forcer, black carbon aerosols in the atmosphere play a vital role in climate change by absorbing solar radiation and altering the formation, lifespan and albedo of clouds. It also provides “seed” for haze formation in urban/regional scale. In northern China, open biomass burning (OBB), such as straw burning after harvesting, is one of important sources of refractory black carbon (rBC). OBB emits both soot particles and substantial amount of semi-volatile organic matters, both of which will undergo a very complicated mixing and evolution processes in the atmosphere to change their ability to form cloud condensation nuclei.