Delhi fourth most polluted city in world: Delhi is the fourth most polluted city in the world, yet the Delhi government's pollution control drive has mostly consisted of "knee jerk reactions" which cause inconvenience to commuters and create chaos on the roads, says an official study.The study on the efficacy of the existing pollution checking system in Delhi by the Central Road Research Institute has found the infrastructure inadequate, the norms for emission standards too liberal and the authenticity of the 'pollution under control' certificates issued by certain authorised stations doubtful.