Considering that the vast majority of the pollution is coming from China I doubt banning cars will make much of difference while highly inconveniencing the public:
Seoul Mayor Park Won-soon said Sunday that his government would seek the power to ban vehicles based on license plate number during days with bad air pollution to reduce the number of cars running on city roads.The Seoul Metropolitan Government plans to request an amendment to the enforcement ordinance of the Clean Air Conservation Act that will allow city mayors and provincial governors to issue a directive that bans cars with even- or odd-numbered license plate numbers from operating on certain days with bad pollution.
The request will be sent to the Ministry of Environment, which has the authority to amend the enforcement ordinance.
“The ban will, in effect, be carried out by the local governments of Seoul and surrounding areas,” said Lee Byung-chul, head of the Seoul government’s air quality policy team. “It cannot be carried out by Seoul alone. We have yet to determine the exact system of how we would enforce the ban, such as having checkpoints to stop odd- or even-numbered license plates from entering the capital area, or whether to utilize police and CCTV cameras to enforce the ban.” [Joong Ang Ilbo]
You can read more at the link.