Which emission control system was the first implemented in vehicles?

The PCV (Positive Crankcase Ventilation) system was the first emission control system implemented in vehicles. Developed in the 1960s, the PCV system was designed to reduce harmful emissions by directing gases that would otherwise escape into the atmosphere back into the engine for combustion. This process not only minimizes air pollution but also improves engine efficiency by reusing unburned fuel and reducing the buildup of harmful substances within the engine.

By incorporating the PCV system, vehicles became more environmentally friendly and helped fulfill early regulations aimed at controlling automotive emissions. The other systems listed were introduced later and, while they are also important for reducing emissions, the PCV system was the pioneer in emission control technology in the automotive industry.