As per CPCB’s findings, of the four main pollutants, only the level of Sulphur Dioxide has gone up from last year. Its level, however, is still below the prescribed standard of 80 micrograms per cubic metre (mcm).

Level of other pollutants like Nitrogen Dioxide, Suspended Particulate Matter (SPM) and Respirable Suspended Particulate Matter (RSPM) has gone down considerably although SPM and RSPM are still way above the prescribed limit.

CPCB officials say the Sulphur Dioxide level could be up as people burst imported crackers that contain sulphur compounds. “Cheap Chinese crackers which contain more sulphur compounds can be one of the probable reasons,’’ said Dr B.Sengupta, Member Secretary of CPCB.

The air pollution was monitored throughout 24 hours yesterday in seven locations—at ITO, Ashok Vihar, Siri Fort, Janakpuri, Nizammuddin, Shahazadabad and Shahdara.

CPCB also monitored the noise level at 13 locations for five hours in the evening. The ambient noise level though went up considerably as compared to a normal day (55-72 decibels as measured on October 17, 2006) but it was again much below last year. It ranged from 56-85 decibels this year as compared to 63-89 in 2005.

CPCB said the rainfall a day before Diwali reduced air pollution. “The favourable meteorological conditions made dust to settle down, lowering the RSPM level. Even the mixing height where pollution mixes with the air was good this year, as much as 198 metres in the night as compared to last year’s 95 metres. This helps in decreasing the pollution level,’’ said Gurnam Singh, Environment Engineer at the CPCB.

“If this trend continues, Delhi will have a quiter Diwali three-four years from now. This change has been mainly due to awareness campaigns by schools, NGOs, the Ministry of Environment and the Delhi Pollution Control Board. Citizens need to be congratulated for bursting less crackers,’’ said Dr Sengupta.

DPCB officials say the fire crackers association has reported a decline in demand by about 40 per cent.