CHENNAI/NEW DELHI (Reuters) - Hundreds of millions of Indians in north India woke up on Sunday to toxic air following Diwali, the Hindu festival of lights, after many revellers defied bans on using firecrackers to celebrate.The capital New Delhi was blanketed with a thick haze, with the average pollution level over 9 times what is considered safe by the World Health Organization. Delhi’s Chief Minister Arvind Kejriwal had banned the use and sale of firecrackers ahead of Diwali, but the policy has been difficult to implement. Revellers in the capital let off huge amounts of fireworks well into Sunday morning, prompting angry residents and environmentalists to complain on social media of breathing difficulties and stinging eyes.