Amid 'severe' air pollution quality in Delhi, Delhi Chief Minister Arvind Kejriwal on Tuesday said the city government will implement the odd-even scheme "whenever required".Speaking to the media, he said the Delhi government was doing its part, but everyone should contribute to reducing the air pollution."People should also think about their role in controlling the pollution level," he said."We will implement the odd-even scheme whenever it will be required," the Chief Minister said.Under the odd-even scheme, vehicles with licence plates ending in an odd number and even number are allowed to ply on alternate days. Implemented first time in 2016, the scheme got into controversies over exemptions granted to various categories of vehicles.Kejriwal also said the Central government should take initiatives in controlling the air pollution."I have met the Union Environment Minister Harsh Vardhan several times in the last one year. The air does not have a boundary. The Centre should take initiative and invite all neighbouring states for consultation for checking air pollution," he said."In October and November, there are around 20-25 days when pollution level increases in Delhi due to stubble burning in neighbouring states. Until the Centre takes steps, nothing cannot be done," Kejriwal said.Kejriwal said that the Delhi government is taking several steps."We have carried out a large-scale tree plantation drive. The government will procure 3,000 buses soon. Also, we sanctioned a large phase of Metro... We are making all efforts on our part," he said.The air quality in Delhi-NCR remained 'severe' for the fourth consecutive day as high humidity, low wind speed and a drop in mercury prevented the dispersal of particulate matters.