With two days of the 18-day relaxation on the CNG deadline given by Supreme Court already gone,e Delhi government has started surprise checks on buses as part of a special drive to ensure that adulteration of low sulphur diesel does not take place in the city.Sources in the Delhi government said that the Transport Department has sent out mobile pollution checking teams. Though the number of such mobile teams could not be immediately known, sources, say, these teams have been placed in "strategic" places across the city like ISBT for such checks.