Emission Control System: Purpose
WARNING: This page is about a different car, the 2005 Toyota Land Cruiser. However, it is still accessible from the selected car via links, so may be relevant.
The emission control systems are installed to reduce the amount of HC, CO and NOx exhausted from the engine ((3) and (4)), to prevent the atmospheric release of blow-by gas-containing HC (1) and evaporated fuel containing HC being released from the fuel tank (2).