Chandigarh, Oct 25: With deterioration in Punjab's air quality index due to stubble burning causing concern, the Punjab Pollution Control Board (PPCB) on Tuesday urged farmers to conserve paddy straw in a scientific manner rather than recklessly burning it. Punjab's Principal Secretary, Science & Technology Roshan Sunkaria said: "The Air Quality Index has deteriorated mainly on account of the fact that the farmers of Punjab have been burning paddy straw at large scale. During the last 4-5 days, the level of pollution has increased tremendously. The situation has further worsened now." "The burning of fire crackers on the day of Diwali, although comparatively much lesser than the last year, and the spurt in stubble burning fires has released particulate matter of PM10 and PM2.5 kind in the air which has raised pollution of air to dangerous levels," he pointed out. Showing deep concern at the increased pollution level, Sunkaria said that the PPCB had issued an advisory asking senior citizens, patients and children to avoid venturing out in the open for a few days and asked the management of schools to ensure that children are not allowed to undertake outdoor activities for the coming days. Sunkaria said the unprecedented increase in pollution levels in the air was hazardous to the health of vulnerable sections of society such as children, students, senior citizens and patients. Farmers in the agrarian state of Punjab burn wheat and paddy straw (stubble) twice a year in April-May and October-November. The problem particularly increases in the winter months when the paddy stubble is burnt by farmers. The Punjab government and its agencies have been warning farmers against burning stubble and even registered cases and imposed penalties on offenders, but the problem continues. 'Green Revolution' state Punjab contributes nearly 50 per cent food grains to the national kitty despite having just 1.54 per cent of the country's geographical area.