The lead content in Delhi was 18 nanogram/cubic metre-60 nanogram/cubic metre with an average of 41 during September (a nanogram is one thousandth of a microgram). The reading for the corresponding period in 1997 was 80-171 with a mean of 118, indicating a dip of 65 per cent. Ninety per cent of the lead in air was attributed to combustion of leaded petrol.

The CPCB's permissible limit for ambient air quality is 1,000 for residential areas and 1,500 for industrial areas. The WHO standard is 500-1,000. This shows that the levels of lead in Delhi are far below the danger mark. The Capital's lead content is monitored at stations in Ashok Vihar, Janakpuri, Siri Fort, Nizammuddin, ITO, Shahjahanabad and Shahdara.

The current figure of 18-60 is, however, based on data collected from residential areas and not busy intersections where the concentration of lead is maximum. The apex pollution monitoring agency, however, does not have the necessary equipment to check the level of benzene in the air. Benzene is emitted by vehicles without catalytic convertors which run on unleaded petrol.