Measurement and Monitoring of Lead

12. The Department of the Environment, Transport and the Regions currently makes measurements of airborne lead at 24 sites across the United Kingdom in a variety of locations (Figure 2). Seven of the sites are located in urban areas, three are located at the kerbside of busy roads, eight sites are close to large lead works and six sites are in rural locations. Table 2 shows the annual average lead concentrations recorded at each of these sites between 1980 and 1996. It can be seen that annual average concentrations in air have decreased at all sites over the 17 year period.
13. Ambient lead concentrations in the United Kingdom are generally measured using the "M-type" sampler, a technique in which air is drawn through a filter at a controlled flow rate allowing suspended particulate matter to be collected. The particulate matter is collected on filters which are changed weekly and are subsequently analysed for lead and at some sites, other metals. The downward facing filter is held in a cylindrical hood primarily for protection from wind and rain. This arrangement has been shown to collect particles which approximate to PM₁₀ * when the wind speed is 6 metres per second close to the average wind speed in the United Kingdom. At four of the rural sites (Chilton, Styrrup, Trebanos and Windermere) the "Hanvell" sampler has been used. This sampler uses the same principle of operation as the "M-type" sampler in that air is drawn through a filter paper, though the design is somewhat different. The filters are changed monthly and are bulked for quarterly analysis for lead and other elements.
14. In recent years the analysis of lead in samples of particulate matter has been undertaken using a variety of spectrometric techniques, whereas, in earlier years other techniques such as X-ray fluorescence were used. Given these different analytical procedures, the accuracy of the data presented in Table 2 is estimated to be between +/- 5 and +/- 15 %.
15. In the mid 1980s annual average concentrations of airborne lead at the kerbside of a busy road in West London were of the order of 1.4 µg/m³ **
    Concentrations measured at urban sites located away from roads were broadly in the range 0.15-0.8 µg/m³.
16. Figure 1 illustrates the decreases in both annual ambient lead concentrations (averaged for urban non- industrial sites) and emissions from petrol engined road vehicles after the reduction in the maximum permissible lead content of petrol from 0.40 to 0.15 grams per litre in 1986. The continuing steady decline in ambient concentrations in subsequent years reflects both the reduction of the lead content of leaded fuel and the increased consumer uptake of unleaded petrol. As a result, urban Levels have reduced to the extent that the maximum values are now of the order of 0.2 µg/m³ even at the west London kerbside site at Cromwell Road.
17. Rural levels, as expected, are rather lower and currently range from about 0.009 to 0.038µg/m³. In industrial areas in the vicinity of processes which emit lead. such as secondary non-ferrous metal smelters, levels can be higher than in urban areas where motor vehicle emissions are the main source of lead. In 1996 annual average concentrations at such sites ranged from about 0.117 to 0.882 µg/m³ (Table 2 and Figure 3).
18. European Council Directive (82/884/EEC), which came into force in 1984, set a limit value for airborne lead concentrations of 2 µg/m³ as an annual average. Concentrations measured at the eight sampling sites around three industrial works in Walsall and Newcastle are used to monitor compliance with this Directive. This limit value was exceeded between 1985 and the end of 1989 at one industrially influenced site in Walsall. This site was in an area which was allowed temporary derogation from compliance with the Directive. Compliance was achieved in 1990, and there have been no further exceedences of the limit value.
19. In their 1987 publication the World Health Organisation set an air quality guideline for lead of between 0.5 and 1.0 µg/m³ as an annual average. The upper value of this guideline was not exceeded at any United Kingdom lead monitoring site in 1996. However two industrial sites in Walsall still exceed the lower limit of the guideline. A WHO working group has recently recommended the revision of this guideline to 0.5 µg/m³ as an annual average. The measurements from the existing monitoring network suggest that the proposed revised WHO guideline is unlikely to be exceeded in the urban environment, even at the kerbside of busy roads. However, this may not be the case in the vicinity of industrial plants which may be significant emitters of airborne lead.

Table 2 Annual average airborne lead concentrations in the United Kingdom, 1980-1996 (µg/m³)

Site Name	1980	1981	1982	1983	1984	1985	1986	1987	1988	1989	1990	1991	1992	1993	1994	1995	1996
Kerbside
Cromwell Rd, London*				1.37	1.41	1.45	0.660	-	-	-	0.380	0.360	0.340	0.255	0.244	0.199	0.151
Cardiff	-	-	-	-	-	1.280	0.630	0.670	0.620	0.570	0.460	0.440	0.384	0.311	0.233	0.165	0.171
Manchester	-	-	-	-	-	2.040	0.810	0.810	0.760	0.640	0.510	0.460	0.339	0.305	0.123	0.133	0.118
Urban
Central London	0.640	0.580	0.630	0.470	0.520	0.480	0.270	0.280	0.300	0.220	-	0.120	0.099	0.078	0.085	0.060	0.074
Brent, London	0.770	0.710	0.890	0.990	-	0.640	0.300	0.290	0.320	-	0.220	0.200	0.174	0.147	0.144	-	0.148
Leeds	0.650	0.370	0.450	0.440	0.280	0.310	0.180	0.190	0.140	-	0.120	-	-	0.106	0.080	0.076	0.060
Motherwell, Strathclyde	0.260	0.230	0.300	0.240	0.180	0.260	0.190	0.180	-	-	0.200	0.160	0.050	0.086	0.023	0.050	0.030
Glasgow	0.460	0.330	0.240	0.420	0.190	0.270	0.120	0.180	0.130	0.140	0.095	0.092	0.093	0.090	0.039	0.051	0.052
Newcastle	-	-	-	-	-	0.180	0.130	0.150	0.110	0.110	0.070	0.070	0.067	0.070	0.027	0.025	0.035
North Tyneside	-	-	-	-	-	0.290	0.150	0.190	0.140	0.120	0.081	0.100	0.083	0.090	0.026	-	-
Rural
Cottered, Hertfordshire	-	-	-	-	0.130	0.130	0.077	0.098	0.076	0.075	0.041	0.045	0.044	0.036	0.019	0.020	0.025
North Petherton, Somerset	-	-	-	-	-	-	0.070	0.065	0.069	0.081	0.053	0.062	-	-	-	-	-
Eskdalemuir, Dumfries and Galloway	-	-	-	-	-	0.029	0.008	0.013	0.014	0.013	0.010	0.013	0.010	0.007	0.006	0.005	0.017
Chilton, Oxfordshire	0.110	0.056	0.066	0.065	0.086	0.090	0.033	0.006	0.052	0.048	0.038	0.038	0.027	0.022	0.025	0.025	0.025
Trebanos, West Glamorgan	0.082	0.080	0.078	0.092	0.098	0.081	0.039	0.048	0.055	0.064	0.043	0.063	0.060	0.037	0.032	0.039	-
Styrrup, Nottinghamshire	0.178	0.135	0.172	0.115	0.170	0.130	0.066	0.070	0.094	0.086	0.057	0.065	0.055	0.035	0.047	0.044	0.038
Windermere, Cumbria	0.047	0.039	0.047	0.045	0.048	0.035	0.024	0.020	0.023	0.021	0.015	0.020	0.008	0.008	0.012	0.013	0.009
Industrial
Walsall Metal Industries 1	-	-	-	-	-	-	0.930	1.370	1.160	0.880	0.470	0.570	0.540	0.570	0.500	0.700	0.579
Walsall Metal Industries 2	-	-	-	-	-	-	2.660	2.950	3.580	2.430	1.300	1.390	1.440	1.220	1.340	1.020	0.882
Walsall Metal Industries 3	-	-	-	-	-	-	0.760	0.730	-	0.640	-	0.340	0.410	-	-	-	-
Walsall Metal Industries 5	-	-	-	-	-	-	-	1.110	1.590	1.380	0.680	0.620	0.680	0.470	0.480	0.660	0.467
**Brookside 1	-	-	-	-	-	-	0.310	0.330	-	0.260	0.150	0.150	0.220	0.160	0.143	0.180	0.177
** Brookside 2	-	-	-	-	-	-	0.990	0.890	1.310	1.100	1.140	0.710	0.560	0.470	0.438	0.465	0.359
*** Elswick 1	-	-	-	-	-	-	-	1.650	1.350	0.530	0.370	0.660	0.340	0.190	0.335	0.480	0.546
*** Elswick 2	-	-	-	-	-	-	-	0.610	0.510	0.600	0.330	0.250	0.230	0.150	0.145	0.140	0.117
*** Elswick 6	-	-	-	-	-	-	-	-	-	0.780	0.450	0.460	0.300	0.190	0.200	0.190	0.215
Note: * the Cromwell Road site closed in September 1997, a new kerbside site at Marylebone Road, London became operational in February 1997. ** sited at Walsall, West Midlands. *** sited in Newcastle.

** 1 µg/m³ is one millionth of a gram of lead in every cubic metre of air.