With diesel buses becoming a part of history, Delhiites have reason to breath easier, literally, according to the pollution levels monitored by the Central Pollution Control board. As analysed by all parameters, there has been a sharp dip on pollution level on 1 December as compared to 24 November on Bahadurshah Zafar Marg. "The decrease in pollution levels could be attributed to the complete removal of diesel buses to a certain extent," said the chairman, CPCB Dr. Dilip Biswas.