Modeling the effects of black carbon and sulfate composition on CCN activation and albedo

With the beginning of the Industrial Revolution came a significant increase in anthropogenic atmospheric emissions, including but not limited to aerosols. Two such primarily anthropogenic aerosols are black carbon (BC), found in soot, and sulfate, from SO2 emissions. Both are often products of combustion processes; however, they differ in that while BC is insoluble as emitted, sulfate is significantly soluble. When BC particles are mixed with sulfate –often produced at the same source– the resulting two-component system is hygroscopic, thus allowing formerly insoluble particles to activate into cloud condensation nuclei (CCN), in accordance with Köhler theory. We simulated a two-component CCN system in which the amounts of insoluble carbon and sulfate were varied. It was found that the CCN number depends on both the amount of sulfate and on initial BC size, and thus both size and sulfate fraction were found to affect the albedo. An increase in regulations of sulfate emissions in recent years has led to a decrease in the sulfateto-black carbon ratio in some regions, while developing regions may see future increases in both emissions. This, combined with the dependence of CCN number on particle composition and size, may result in a change in activation of black carbon. The effects seen here may have significant implications for climate mitigation strategies.