The burden is summed from 200 hPa to the model top at 10 hPa. ( A) Burden remaining from a 2 Tg year −1 of SO 2 injection at 20 km (dotted line), at 13.5 km (dashed line), and at 13.5 km including BC (solid line). For each scenario, the injection was over a 10-day period every June at the equator. ( B) Burden for the injection at 13.5 km including BC in latitude bands: Solid line is global, dashed line is 30°N to 30°S, dotted line is 30°N to 90°N, and dash-dotted line is 30°S to 90°S. The model is running in a free mode, so there is natural variability in the dynamics impacting the aerosol loading from year to year. It takes approximately 2 years to reach a pseudo equilibrium loading, and interannual variability is apparent in the last 4 years plotted.