New Delhi, Oct 26 Stubble-burning in Delhi's neighbouring Punjab and Haryana is currently contributing to 20-30 per cent of the Capital's overall air-pollution, at a time when winds over Delhi are calm, officials said.Central Pollution Control Board (CPCB) officials said Haryana and Punjab are monitoring the fire incidents, including stubble-burning, and apprising them of the situation on a daily basis."There are local polluting factors such as vehicular pollution and dust, but stubble-burning in Punjab and Haryana is contributing about 20-30 per cent to the Delhi's air pollution," said Prashant Gargava, member secretary CPCB.The assessment is based on the data from IITM-Pune, he said."The wind height could be a reason behind it. Apart from that, winds in Delhi currently don't have a definite direction," he added.The CPCB however warns that the wind direction may change to northerly and north-westerly around November 7, the time of Diwali, which may lead to severe drop in Delhi's air quality.Stubble-burning is done by farmers, the resultant smoke takes the form of smog when it reaches Delhi and regions around it leading to a spike in air pollution. Generally, the first week of November is the time of smog in Delhi, when the air quality reaches beyond severe.