The concentration of lead in the air at a site on the M4 motorway has been monitored annually since 1971. Results are given for the years 1984-1987. During this period (January 1986), the maximum permitted lead content of petrol sold in the UK was reduced from 0.4 to 0.15 g/l and this caused a corresponding reduction in the average airborne lead concentration, from typically 9 micro gram per cubic metre to less than 3 micro gram per cubic metre. For earlier reports see IRRD 22140, 210694, 254627 and 280378.

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