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Lead concentrations in U.K. urban air
Atmospheric EnvironmentVol.27B,No. 2, pp. 265 268.1993. Printed in Great Britain.
0957 1272/93$6.00+0.00 PergamonPress Ltd
L E A D C O N C E N T R A T I O N S IN U.K. U R B A N AIR K. W. NICHOLSON a n d J. R. BRANSON AEA Environment and Energy, Harwell Laboratory, Oxon OXl 1 0RA, U.K. (First received 29 April 1992 and in final fi)rm 30 October 1992)
Abstrac~Atmospheric concentrations of lead have been measured at two sites in each of two cities in the U.K. (London and Manchester). The results have been used to evaluate the effect of the increasing use of unleaded petrol (gasoline) in motor vehicles. Atmospheric concentrations of lead measured in London were found to be correlated to the U.K. lead in petrol consumption figures. However, a similar correlation was not evident for Manchester indicating the importance of other sources of atmospheric lead. Lead concentrations were correlated between the two cities and a large variation in measured levels illustrates the importance of meteorological effects in determining atmospheric concentration. Key word index: Atmospheric concentration, gasoline, motor vehicles, lead, petrol.
INTRODUCTION In an attempt to reduce atmospheric lead concentrations in the U.K., the permissible level of lead in petrol (gasoline) was reduced from 0.4 to 0.15 g { - a in January 1986. However, the use of unleaded petrol (defined as having a lead content less than 0.02 g ( - ~ ) was limited with only one motorist in 2000 buying the product in March 1988 (Hughes, 1991). The introduction of reduced levels of duty on unleaded petrol and the increasing numbers of new cars which have been able to run on unleaded fuel have resulted in steadily decreasing sales of leaded petrol. The reduction in the use of leaded petrol seems likely to result in a decrease in atmospheric concentrations as seen in the U.S.A. (Nriagu, 1990). However, the importance of such a decrease in relation to human health is open to some debate (Lynam and Pfeifer, 1991). Accompanying reductions in the lead content of soil, vegetation and run-off will be likely to occur, but the slow removal processes mean that this accompanying decrease may be delayed (Ball et al., 1991). This note describes the effect of a reduction in the use of leaded petrol on atmospheric concentrations measured in two urban areas in the U.K.
EXPERIMENTAL Over about the last 15 years, atmospheric lead concentrations have been measured at two sites in London (Borough of Brent in northwest London) and at two sites in the city of Manchester using the technique described by Pattenden and Branson (1987). Greater Manchester has a population around 2.5 million and is located approximately 250 km northwest of Central London (population of Greater London: 9.5 million). At each sampling location, atmospheric particulates were collected on 6-cm diameter Whatman 40 filters aspirated at approximately 7E min-~. A cylindrical polypropylene sampling head was used to protect and sup©1993. United Kingdom Atomic Energy Authority. 265
AE(B) 27:2-d
port the filters and the 1-cm diameter inlet to the head was directed downwards. Pattenden and Wiffen (1977) have studied the collection characteristics of this type of sampler in a wind tunnel and deduced an approximate upper cut-off of 6 #m, with particles smaller than this diameter being collected by the sampler. The filters at each site are changed at monthly intervals and the total volume of air aspirated during each sampling period is determined using a flowmeter. The collected particulates are analysed by X-ray fluorescence, using methods described by Grennfelt et al. (1971) with minor modifications. Calibration is achieved using unexposed filters onto which known amounts of standard solution are allowed to dry. The lead content of all collected particulates has been found to be at least five times the detection limit. Despite the use of identical samplers and analytical procedures, there are some differences in sampling protocol according to site. These were introduced for security reasons. However, all samples have'been collected within 5 m of ground level and were taken in largely residential areas.
RESULTS Monthly consumption figures of leaded petrol (gasoline) have been obtained from the Institute of Petroleum and the mean lead content of 0.14 g f (U.K. Petroleum Industry Association) has been used to calculate the mean monthly lead emission figures for the U.K. The emission levels are plotted with the atmospheric lead concentration for Brent and Manchester (determined as the average for the two measurement sites) in Fig. 1. A gradual decline in atmospheric concentration for the period March 1988-October 1991, at both sites, accompanies the decrease in lead emissions from car exhausts. However, a strong seasonal effect is also apparent which results in high atmospheric concentrations in some of the winter months. A similar effect has been observed by Pattenden and Branson (1987) for lead levels in urban air during the mid-1980s, which they attributed to the presence of temperature inversions that restricted pollutant dispersal. Similar seasonal trends of
266
K.W. NICHOLSONand J. R. BRANSON 1200
1000"
E
800" 600"
i
i il
;i ~
8
il
Manchester ......... Brent - UKleadconsumption
-
8 460" I.
."',./'I
".
'.. /,.ii~"
4
.-'.,
200"
• , " , - , • , - , - , - , 0
Month
Fig. 1. Monthly mean concentrations of airborne lead in Brent and Manchester and U.K. lead in petrol consumption figures (March 1988-October 1991).
1200
E ~
1200 "
1000
I(X}O " ~
..=
800' ~
.~.
800"
.=.
-i ~
200"
~
0
-.....
600"
•
200 "
0
4
8
12
0
. • 200
UK lead consumption (t day
i • 400
.
, 600
.
, 800
.
•
.
1000
, 1200
-I)
Airborne lead concentration in Brent (ng
Fig. 2. Correlation between the monthly airborne lead concentrations in Brent and U.K. lead in petrol consumption figures (March 1988-October 1991)•
other trace elements have been found which cannot be explained by fluctuations in domestic fuel consumption (e.g. Cawse, 1987). It is important to note that the seasonal fluctuations may be considerably greater than the decrease in concentration because of the increasing use of lead-free petrol. The correlation between atmospheric lead concentration and automotive lead consumption is best illustrated for Brent (r= 0.38; 34 d.f. significant at the 5% level). This correlation is illustrated in Fig. 2. It must be remembered, however, that the seasonal fluctuations increase scatter and decrease the correlation coefficient. A similar correlation for Manchester was not significant and this may be a reflection of lower contributions of atmospheric lead from vehicle exhausts, in relation to other sources. The seasonal
m -3)
Fig. 3. Correlation between the monthly airborne lead concentrations in Brent and Manchester (March 1988-October 1991).
fluctuations in atmospheric lead could also mask any correlation. For a full assessment of the effects of reduced lead consumption on atmospheric lead concentration in Manchester, a much longer measurement period is required. It is significant, however, that monthly mean atmospheric concentrations in Manchester and Brent were highly correlated (r = 0.89; 33 d.f. significant at the 0.1%o level; see Fig. 3). Such a correlation can be explained by the lead in each city being primarily of local origin and the meteorological conditions in the two cities being correlated. The relatively small decrease in atmospheric lead concentration with increasing use of unleaded fuel contrasts with much larger decreases reported for rural areas in the U.K. (Playford, 1992). The decrease in rural areas probably reflects their remoteness from other sources
Lead concentration in U.K. urban air 1200
267
30
1000
800 '
20
"o
a
g':mc~ster ......... Brent - UK leadconsumption
. . . . . . . . . . . . . .
•.~
400"
10 ,,,,1
200"
t
0---
, • , • ,
-
, - , • , • , • ,
0
Month
Fig. 4. Running annual means of atmospheric lead concentrations and U.K consumption of lead in petrol (December 1982-April 1991).
of atmospheric lead and the importance of the contribution of automobile emissions to atmospheric lead prior to the decreased consumption of leaded fuel. Figure 4 illustrates the general relationship between the running annual mean atmospheric lead concentrations for Brent and Manchester and the U.K. lead in petrol consumption. The use of the running mean is included to reduce the impact of seasonal fluctuations. The sharp drop in lead consumption in December 1985 was due to a change in the legal limit of lead in petrol from 0.4 to 0.15 g f x. The accompanying drop in atmospheric lead content has been previously noted (Pattenden and Branson, 1987; Jensen and Laxen, 1987) and can be seen in comparison to the effects of an increased use of lead-free petroleum in Fig. 4. It is important to consider the nature of atmospheric lead originating from automobile exhausts. Such material is generally associated with small, easily respirable particles (less than around 5/~m diameter), although material resuspended from vehicular exhaust systems may be larger. In any event, it can be considered that only the material of respirable size was determined as atmospheric lead in the current study. Atmospheric lead has usually been associated with blood lead levels (Sinn, 1980; Chamberlain, 1983) but, as emissions decrease, the relative importance of blood lead originating from previous deposits will increase, Such lead, if resuspended, is likely to be associated with large particles which are not readily inhaled. However, this lead may be important in the contamination of food crops grown in urban areas and this may lead to ingestion. While levels of lead in street dust are likely to reflect the lead content of petrol, it seems probable that lead levels associated with soilderived particles will decrease less rapidly. In summary, the use of lead-free petrol (gasoline) in motor vehicles has continued to increase in the U.K. and this has resulted in some decrease in atmospheric
lead. Seasonal fluctuations in atmospheric concentration are high, however, and variations can greatly outweigh the differences in atmospheric lead due to the increasing use of unleaded fuel. Acknowledgements--We thank our colleaguesMr J. Watling
for the lead analyses and Mrs C. Larnach for sample preparation. We also thank the Chief Environmental Health Officers and their staff in the London Borough of Brent and the City of Manchester for operating the sampling stations and for financial support from these authorities. The helpful comments of J. A. Garland are gratefully acknowledged. We are thankful for the comments of three referees.
REFERENCES
Ball D. J., Hamilton R. S. and Harrison R. M. (1991) The influenceof highway related pollutants on environmental quality. In Highway Pollution (edited by Hamilton R. S. and Harrison R. M.), pp. 1-47. Elsevier, Amsterdam. Cawse, P. A. (1987) Trace and Major Elements in the Atmosphere at Rural Locations in Great Britain, 1972-1981. British Ecological Society Special Publications Series on Pollutant Transport and Fate in Ecosystems, Blackwells, Oxford. Chamberlain A. C. (1983) Effect of airborne lead on blood lead. Atmospheric Environment 17, 677-692. Grennfelt P., Askerstrom A, and Brosset C. (1971) Determination of filter-collected airborne matter by X-ray fluorescence. Atmospheric Environment 5, 1-6. Hughes D. (1991) Legislation relating to highway pollution. In Highway Pollution (edited by Hamilton R. S. and Harrison R. M.), pp. 453-500. Elsevier, Amsterdam. Jensen R. A. and Laxen D. P. H. (1987)The effect of the phase down of lead in petrol on levels of lead in air. Sci. Total Envir. 59, 1-8. Lynam D. R. and PfeiferG. D. (1991)Human health effects of highway-related pollutants. In Highway Pollution (edited by Hamilton R. S. and Harrison R. M.), pp. 259-280. Elsevier, Amsterdam. Nriagu J. O. (1990) The rise and fall of leaded gasoline. Sci. Total Envir. 92, 13-28.
268
K.W. NICHOLSON and J. R. BRANSON
Pattenden N. J. and Branson J. R. (1987) Relation between lead in air and in petrol in two urban areas of Britain. Atmospheric Environment 21, 2481-2483. Pattenden N. J. and Wiffen R. D. (1977) The particle size dependence of the collection efficiency of an environmental aerosol sampler. Atmospheric Environment 11, 677-681.
Playford K. (1992) Personal Communication, AEA Environment and Energy, Harwell Laboratory, Oxon OX11 0RA, U.K. Sinn W. (1980) On the relationship between lead in air and blood lead content of persons living and working in the centre of a city. Int. Archs occup, envir. Hlth 47, 93-118.
0957 1272/93$6.00+0.00 PergamonPress Ltd
L E A D C O N C E N T R A T I O N S IN U.K. U R B A N AIR K. W. NICHOLSON a n d J. R. BRANSON AEA Environment and Energy, Harwell Laboratory, Oxon OXl 1 0RA, U.K. (First received 29 April 1992 and in final fi)rm 30 October 1992)
Abstrac~Atmospheric concentrations of lead have been measured at two sites in each of two cities in the U.K. (London and Manchester). The results have been used to evaluate the effect of the increasing use of unleaded petrol (gasoline) in motor vehicles. Atmospheric concentrations of lead measured in London were found to be correlated to the U.K. lead in petrol consumption figures. However, a similar correlation was not evident for Manchester indicating the importance of other sources of atmospheric lead. Lead concentrations were correlated between the two cities and a large variation in measured levels illustrates the importance of meteorological effects in determining atmospheric concentration. Key word index: Atmospheric concentration, gasoline, motor vehicles, lead, petrol.
INTRODUCTION In an attempt to reduce atmospheric lead concentrations in the U.K., the permissible level of lead in petrol (gasoline) was reduced from 0.4 to 0.15 g { - a in January 1986. However, the use of unleaded petrol (defined as having a lead content less than 0.02 g ( - ~ ) was limited with only one motorist in 2000 buying the product in March 1988 (Hughes, 1991). The introduction of reduced levels of duty on unleaded petrol and the increasing numbers of new cars which have been able to run on unleaded fuel have resulted in steadily decreasing sales of leaded petrol. The reduction in the use of leaded petrol seems likely to result in a decrease in atmospheric concentrations as seen in the U.S.A. (Nriagu, 1990). However, the importance of such a decrease in relation to human health is open to some debate (Lynam and Pfeifer, 1991). Accompanying reductions in the lead content of soil, vegetation and run-off will be likely to occur, but the slow removal processes mean that this accompanying decrease may be delayed (Ball et al., 1991). This note describes the effect of a reduction in the use of leaded petrol on atmospheric concentrations measured in two urban areas in the U.K.
EXPERIMENTAL Over about the last 15 years, atmospheric lead concentrations have been measured at two sites in London (Borough of Brent in northwest London) and at two sites in the city of Manchester using the technique described by Pattenden and Branson (1987). Greater Manchester has a population around 2.5 million and is located approximately 250 km northwest of Central London (population of Greater London: 9.5 million). At each sampling location, atmospheric particulates were collected on 6-cm diameter Whatman 40 filters aspirated at approximately 7E min-~. A cylindrical polypropylene sampling head was used to protect and sup©1993. United Kingdom Atomic Energy Authority. 265
AE(B) 27:2-d
port the filters and the 1-cm diameter inlet to the head was directed downwards. Pattenden and Wiffen (1977) have studied the collection characteristics of this type of sampler in a wind tunnel and deduced an approximate upper cut-off of 6 #m, with particles smaller than this diameter being collected by the sampler. The filters at each site are changed at monthly intervals and the total volume of air aspirated during each sampling period is determined using a flowmeter. The collected particulates are analysed by X-ray fluorescence, using methods described by Grennfelt et al. (1971) with minor modifications. Calibration is achieved using unexposed filters onto which known amounts of standard solution are allowed to dry. The lead content of all collected particulates has been found to be at least five times the detection limit. Despite the use of identical samplers and analytical procedures, there are some differences in sampling protocol according to site. These were introduced for security reasons. However, all samples have'been collected within 5 m of ground level and were taken in largely residential areas.
RESULTS Monthly consumption figures of leaded petrol (gasoline) have been obtained from the Institute of Petroleum and the mean lead content of 0.14 g f (U.K. Petroleum Industry Association) has been used to calculate the mean monthly lead emission figures for the U.K. The emission levels are plotted with the atmospheric lead concentration for Brent and Manchester (determined as the average for the two measurement sites) in Fig. 1. A gradual decline in atmospheric concentration for the period March 1988-October 1991, at both sites, accompanies the decrease in lead emissions from car exhausts. However, a strong seasonal effect is also apparent which results in high atmospheric concentrations in some of the winter months. A similar effect has been observed by Pattenden and Branson (1987) for lead levels in urban air during the mid-1980s, which they attributed to the presence of temperature inversions that restricted pollutant dispersal. Similar seasonal trends of
266
K.W. NICHOLSONand J. R. BRANSON 1200
1000"
E
800" 600"
i
i il
;i ~
8
il
Manchester ......... Brent - UKleadconsumption
-
8 460" I.
."',./'I
".
'.. /,.ii~"
4
.-'.,
200"
• , " , - , • , - , - , - , 0
Month
Fig. 1. Monthly mean concentrations of airborne lead in Brent and Manchester and U.K. lead in petrol consumption figures (March 1988-October 1991).
1200
E ~
1200 "
1000
I(X}O " ~
..=
800' ~
.~.
800"
.=.
-i ~
200"
~
0
-.....
600"
•
200 "
0
4
8
12
0
. • 200
UK lead consumption (t day
i • 400
.
, 600
.
, 800
.
•
.
1000
, 1200
-I)
Airborne lead concentration in Brent (ng
Fig. 2. Correlation between the monthly airborne lead concentrations in Brent and U.K. lead in petrol consumption figures (March 1988-October 1991)•
other trace elements have been found which cannot be explained by fluctuations in domestic fuel consumption (e.g. Cawse, 1987). It is important to note that the seasonal fluctuations may be considerably greater than the decrease in concentration because of the increasing use of lead-free petrol. The correlation between atmospheric lead concentration and automotive lead consumption is best illustrated for Brent (r= 0.38; 34 d.f. significant at the 5% level). This correlation is illustrated in Fig. 2. It must be remembered, however, that the seasonal fluctuations increase scatter and decrease the correlation coefficient. A similar correlation for Manchester was not significant and this may be a reflection of lower contributions of atmospheric lead from vehicle exhausts, in relation to other sources. The seasonal
m -3)
Fig. 3. Correlation between the monthly airborne lead concentrations in Brent and Manchester (March 1988-October 1991).
fluctuations in atmospheric lead could also mask any correlation. For a full assessment of the effects of reduced lead consumption on atmospheric lead concentration in Manchester, a much longer measurement period is required. It is significant, however, that monthly mean atmospheric concentrations in Manchester and Brent were highly correlated (r = 0.89; 33 d.f. significant at the 0.1%o level; see Fig. 3). Such a correlation can be explained by the lead in each city being primarily of local origin and the meteorological conditions in the two cities being correlated. The relatively small decrease in atmospheric lead concentration with increasing use of unleaded fuel contrasts with much larger decreases reported for rural areas in the U.K. (Playford, 1992). The decrease in rural areas probably reflects their remoteness from other sources
Lead concentration in U.K. urban air 1200
267
30
1000
800 '
20
"o
a
g':mc~ster ......... Brent - UK leadconsumption
. . . . . . . . . . . . . .
•.~
400"
10 ,,,,1
200"
t
0---
, • , • ,
-
, - , • , • , • ,
0
Month
Fig. 4. Running annual means of atmospheric lead concentrations and U.K consumption of lead in petrol (December 1982-April 1991).
of atmospheric lead and the importance of the contribution of automobile emissions to atmospheric lead prior to the decreased consumption of leaded fuel. Figure 4 illustrates the general relationship between the running annual mean atmospheric lead concentrations for Brent and Manchester and the U.K. lead in petrol consumption. The use of the running mean is included to reduce the impact of seasonal fluctuations. The sharp drop in lead consumption in December 1985 was due to a change in the legal limit of lead in petrol from 0.4 to 0.15 g f x. The accompanying drop in atmospheric lead content has been previously noted (Pattenden and Branson, 1987; Jensen and Laxen, 1987) and can be seen in comparison to the effects of an increased use of lead-free petroleum in Fig. 4. It is important to consider the nature of atmospheric lead originating from automobile exhausts. Such material is generally associated with small, easily respirable particles (less than around 5/~m diameter), although material resuspended from vehicular exhaust systems may be larger. In any event, it can be considered that only the material of respirable size was determined as atmospheric lead in the current study. Atmospheric lead has usually been associated with blood lead levels (Sinn, 1980; Chamberlain, 1983) but, as emissions decrease, the relative importance of blood lead originating from previous deposits will increase, Such lead, if resuspended, is likely to be associated with large particles which are not readily inhaled. However, this lead may be important in the contamination of food crops grown in urban areas and this may lead to ingestion. While levels of lead in street dust are likely to reflect the lead content of petrol, it seems probable that lead levels associated with soilderived particles will decrease less rapidly. In summary, the use of lead-free petrol (gasoline) in motor vehicles has continued to increase in the U.K. and this has resulted in some decrease in atmospheric
lead. Seasonal fluctuations in atmospheric concentration are high, however, and variations can greatly outweigh the differences in atmospheric lead due to the increasing use of unleaded fuel. Acknowledgements--We thank our colleaguesMr J. Watling
for the lead analyses and Mrs C. Larnach for sample preparation. We also thank the Chief Environmental Health Officers and their staff in the London Borough of Brent and the City of Manchester for operating the sampling stations and for financial support from these authorities. The helpful comments of J. A. Garland are gratefully acknowledged. We are thankful for the comments of three referees.
REFERENCES
Ball D. J., Hamilton R. S. and Harrison R. M. (1991) The influenceof highway related pollutants on environmental quality. In Highway Pollution (edited by Hamilton R. S. and Harrison R. M.), pp. 1-47. Elsevier, Amsterdam. Cawse, P. A. (1987) Trace and Major Elements in the Atmosphere at Rural Locations in Great Britain, 1972-1981. British Ecological Society Special Publications Series on Pollutant Transport and Fate in Ecosystems, Blackwells, Oxford. Chamberlain A. C. (1983) Effect of airborne lead on blood lead. Atmospheric Environment 17, 677-692. Grennfelt P., Askerstrom A, and Brosset C. (1971) Determination of filter-collected airborne matter by X-ray fluorescence. Atmospheric Environment 5, 1-6. Hughes D. (1991) Legislation relating to highway pollution. In Highway Pollution (edited by Hamilton R. S. and Harrison R. M.), pp. 453-500. Elsevier, Amsterdam. Jensen R. A. and Laxen D. P. H. (1987)The effect of the phase down of lead in petrol on levels of lead in air. Sci. Total Envir. 59, 1-8. Lynam D. R. and PfeiferG. D. (1991)Human health effects of highway-related pollutants. In Highway Pollution (edited by Hamilton R. S. and Harrison R. M.), pp. 259-280. Elsevier, Amsterdam. Nriagu J. O. (1990) The rise and fall of leaded gasoline. Sci. Total Envir. 92, 13-28.
268
K.W. NICHOLSON and J. R. BRANSON
Pattenden N. J. and Branson J. R. (1987) Relation between lead in air and in petrol in two urban areas of Britain. Atmospheric Environment 21, 2481-2483. Pattenden N. J. and Wiffen R. D. (1977) The particle size dependence of the collection efficiency of an environmental aerosol sampler. Atmospheric Environment 11, 677-681.
Playford K. (1992) Personal Communication, AEA Environment and Energy, Harwell Laboratory, Oxon OX11 0RA, U.K. Sinn W. (1980) On the relationship between lead in air and blood lead content of persons living and working in the centre of a city. Int. Archs occup, envir. Hlth 47, 93-118.