Schematic diagram of gas flow inside the GCMS through ion source 1. The eight blue hexagons and three red cylinders are the valves and leaks, respectively, and they have been labeled similarly to the instrument diagram in Niemann et al. (2002) paper. Gas flows through L1, L2, and L3 at different times during the mission. The valves were used for specific purposes and their functions are mentioned in Niemann et al. (2002). Dotted blue circles represent the possible sources of aerosol accumulation in the GCMS (explained in Section 4.2.3)