Sources of Lead in Air

5. Lead occurs in the earth's crust and is released naturally through various processes including weathering of rocks, volcanic activity, and uptake and subsequent release from plants. Anthropogenic sources of lead stem from its removal from the earth's crust. It is released into the atmosphere through the mining and smelting of ores, the production, use, recycling and disposal of leadcontaining products and the burning of fossil fuels. Industrial emissions and a large part of the vehicle emissions are in the form of particles of inorganic compounds of lead. Primary lead particles emitted from petrol vehicles are around 0.015 µm* in diameter and these aggregate to form larger particles with diameters of 0.1-1.0 µm; these particles can remain in the air for 7-24 days. Industrially emitted particles are around 0.1-5.0 µm in diameter depending on the process and the nature of the control devices employed.
6. The main sources of national airborne lead emissions in the United Kingdom for 1995 are shown in Table 1. Currently the dominant contribution is from petrol combustion at 1067 tonnes per annum. This results from the use of lead as an additive to increase the octane rating. In January 1986 the maximum permitted lead content of petrol was reduced from 0.40 to 0.15 grams per litre (g/l), and since then there has been a progressive increase in use of unleaded petrol to its current level of over 70% of the market. As a result, lead emissions into the air from petrol engined road vehicles in the United Kingdom have more than halved since 1987 (Figure 1). Under European Community legislation likely to be adopted in 1998, the marketing and sale of leaded petrol will be banned throughout the community from the year 2000, except in a limited number of specified circumstances. There are other sources of lead in air in addition to the lead emitted in motor exhausts. These include coal combustion, the production of non-ferrous metals and waste treatment and disposal.

Table 1. Estimated United Kingdom emissions of lead by emission source, 1995 (tonnes)

Source	Emissions (tonnes)	Percentage of Total*
Power Station Combustion	28	2
Commercial/Institutional/Residential Combustion	13	1
Industrial Combustion Plants and Processes
Combustion Plant	44	3
Lead/Zinc/Copper	139	9
Other	31	2
Non-Combustion Processes
Coke Ovens	1	<1
Iron and Steel Production	36	2
Chemical Processes	2	<1
Road Transport
Petrol	1067	73
Diesel	1	<1
Waste Treatment and Disposal	105	7
Total	1468	100
Note: * Rounded to nearest 1%

* 1µm is one millionth of a metre