"The assessment of CPCB has revealed no clear trend and wide fluctuation observed in the concentration. It is evident that the meteorology and emissions from other polluting sources have been major factors impacting air quality of Delhi during the period," Environment minister Prakash Javadekar said in a written reply.

He said higher wind speeds and mixing height in general result in better dispersion and lower pollution levels.

"Overall it can be stated that while some reduction in air pollution is likely to happen due to odd-even scheme, a single factor or action cannot substantially reduce air pollution levels in Delhi. Therefore, a comprehensive set of actions following an integrated approach is required to make substantial improvement in air quality," he said.