Recent Trends in Atmospheric Lead Levels at an UrbanIndustrial District of Metropolitan Lisbon, Portugal,
through PIXE Analysis of Air-Particulate Matter
M. Carmo Freitas1, Miguel A. Reis1, and Adriano M.G. Pacheco2
1
ITN – Nuclear and Technological Institute, Estrada Nacional 10, 2686-953 Sacavém, Portugal
2
CVRM-IST – Technical University of Lisbon, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
Abstract. Despite a steep decline in primary, traffic-related loads, lead in the environment is still much of an issue. Current
atmospheric levels may be unmistakably reflecting the widespread use of cleaner fuels, yet decades of uncontrolled emissions
from mobile sources have made lead to pervade every terrestrial (and aquatic) ecosystem, from where it keeps re-entering the
lower troposphere, at least in terms of local circulation. The continuing surveillance of airborne-lead levels is thus necessary,
not just for ensuring a strict compliance with regulatory decisions, but also for assisting in the implementation of remediation
and/or rehabilitation policies. In Portugal, unleaded gasoline was made generally available in 1990, yet both leaded and leadfree varieties were commercialised until 1998. After that, all vehicles were compelled to use unleaded gasoline. Even though
it is certainly too early for a full trend analysis of airborne levels and their response to the ban on lead, concentrations in
ambient air over an important urban-industrial corridor within the Lisbon metropolitan area show a steady, sharp decrease
through the last decade. Since 2000, airborne-lead data seems somewhat stabilised and, as far as busy conurbations are
concerned, roughly within the values that were usually observed in the rural hinterland back in the mid 1990s.
This is indeed a major concern, since ultrafine particles
(EAD < 0.1 µm) form an overall majority (in number)
from either diesel or spark-ignition engines [5-8]. Lead
accumulating in human bones and teeth has also been
ascribed an extended time of residence of over 10 and
up to 20 years, respectively.
Limits for lead concentrations in ambient air were set
in a few countries as a recognition of such detrimental
effects. The EU legislation is relatively recent [9], and
it has currently settled for 500 ng m-3 in air particulate
matter with EAD < 10 µm (PM10), for 24-h periods.
PIXE is one of the most powerful (and fast) analytical
techniques for lead determination. A large number of
aerosol studies and surveys using the PIXE analysis
have been reported, e.g. [10-15]. PIXE results for Pb
concentrations in fine and coarse particulates, sampled
along an important urban-industrial corridor within the
Lisbon metropolitan area since 1994, are given herein.
INTRODUCTION
Several classic monographs have described the toxic
properties of lead and its compounds [1], and high
exposures in previous times have been documented [2].
Lead emissions were then mostly of industrial origin,
and emissions from mobile sources were not wellknown yet or not even relevant at all. With the increase
in motorised transit – mainly city-core and commuter
traffic, with large periods of congestion/stop-and-go
and engines running idle – lead emissions became not
only heavier in general, but also riskier to younger and
younger age groups, increasing lead contents in the
blood of born and unborn children. About as much as
40 % of the total lead intake enters the human body via
inhalation – for instance, see [3] and references therein.
Lead is not an essential element for human nutrition
and/or health, and nearly all lead in blood appears to
reflect some degree of exposure to sources relating to
anthropogenic activities [4]. Unexposed individuals or
populations, often referred to as "controls" in surveys,
do not really exist anymore. Lead from car exhausts
mainly consists of PbBrCl particles with an equivalent
aerodynamic diameter (EAD) below 0.5 µm. On the
other hand, it is generally accepted that ca. 40 % of the
inhaled lead under 0.05 µm is deposited deep into the
respiratory tract, down to the innermost alveolar levels.
EXPERIMENTAL
Airborne particulates have been collected by a Gent
stacked-filter unit (SFU) sampler, that separates the
PM2.5 from the PM10 fraction on Nucleopore 47-mm
diameter polycarbonate filters with 0.4 and 8.0 µm
pore sizes [16,17]. After gravimetry for mass loads,
one quarter of each filter was analysed by PIXE [18].
CP680, Application of Accelerators in Research and Industry: 17th Int'l. Conference, edited by J. L. Duggan and I. L. Morgan
© 2003 American Institute of Physics 0-7354-0149-7/03/$20.00
456
TABLE 2. Concentration of lead at Carregado (in ng m-3).
In 1993, a collector was installed at one of the Lisbon
government-run, air-monitoring facilities. The site is
located in the Lisbon SE (Beato zone), approx. 7km
from the city centre but still an inner-city location [13].
Samples were collected for 24-h periods on a twice-aweek basis (one weekend day plus one mid-week day),
October 1993 through January 1995. Only 40 min out
of each hour were used for collection, in a total of 16h
per filter.
In 1995, air filtering was limited to 10 min every 4 h,
for 2-week times, totalling 14 h of sampling per filter.
This new site was at Carregado, approx. 30 km from
Lisbon centre [19]. The equivalence between this type
of collection and the former, more traditional format –
that is, 24-h sampling periods, twice a week – has been
discussed earlier [12].
Since 1999, the collector runs continuously, again in
24-hour periods, and now at the ITN campus (Nuclear
and Technological Institute – Bobadela), some 14 km
from the city centre. Sampling is carried out twice a
week, one weekend day plus one mid-week day at a
time. All three sampling locations – Beato, Carregado,
Bobadela – are in an urban-industrial, heavily travelled
(especially during rush hours) corridor, that roughly
parallels the Tagus river mouth.
Mar. 1995 ∗ Feb. 1996
PM10
Samples
86
87
89
Mean
111
63.3
170
Median
88.2
31.0
114
Max.
409
545
953
Min.
20.0
3.88
10.7
26
26
26
Mean
40.2
47.3
85.2
Max.
90.4
248
322
Samples
1999
2000
Finer Coarser PM10
Finer Coarser PM10
50
37
54
54
28
55
Mean
31.6
24.8
46.3
11.8
4.75
14,0
Median
11.2
7.22
16.2
8.86
2.93
11.1
Max.
379
242
621
51.9
16.6
57.4
Min.
4.94
3.24
5.01
1.2
0.424
1.2o
2001
2002
Finer Coarser PM10
Finer Coarser PM10
Samples
100
51
101
60
31
60
Mean
8.6
6.22
11.6
15
8.29
19.2
Median
6.11
3.67
6.80
7.60
6.40
9.98
Max.
64.2
34.6
98.8
172
23.4
181
Min.
1.48
1.22
1.48
2.08
0.63
2.08
Considering the present legal dispositions, the mean
concentrations have never exceeded the legislated
value for PM10 – 500 ng m-3. At Beato (1993-1995)
and Bobadela (1999), the maximum concentrations did
exceed that value though. The Tables indicate that
concentrations are decreasing as well, and Figures 1-3
reveal that such a smooth trend appears to be levelling
off since 2000, for PM10 and the other two particulate
fractions. This constant value is already lower than the
lead concentration at rural areas in the early 1990s, as
shown in Table 4 for Tapada do Outeiro, an opencountryside area.
A recent contract report concludes that, from 1999,
lead concentrations in metropolitan Lisbon tend to be
lower in summer than in other seasons [21] – Figure 4.
This may be due to typical (meteorological) conditions,
and to some joint effect of traffic reduction and factory
closures for the holiday season, and seems to be an
urban trend in Europe [22,23] A larger scattering in
data can also be observed for autumn and winter terms.
TABLE 1. Concentration of lead at Beato (in ng m-3).
Coarser
PM10
TABLE 3. Concentration of lead at Bobadela (in ng m-3).
The ability of epiphytic lichens to monitor airborne
lead, even down to its isotopic composition, seems
unquestionable [20]. Likewise, it was possible to map
lead concentrations throughout mainland Portugal from
results of a lichen-based survey held in 1993 [14,19].
Lead was most prevalent along the Lisbon-Setúbal axis
and its origin most likely car exhaust. As so, we went
through all data available for lead concentrations in
aerosol samples since 1994 until now, as such a period
encompasses the transition from leaded to unleaded
gasoline in Portugal.
Tables 1-3 list the basic data for lead concentrations
in aerosols' finer, coarser and PM10 (finer + coarser)
fractions, at the above sites from 1994 to 2002.
Finer
Coarser
Samples
RESULTS AND DISCUSSION
Oct. 1993 ∗ Jan. 1995
Finer
457
TABLE 4. Concentration of lead at a rural area (in ng m-3),
taken as a baseline for non-enforced, unleaded-gasoline use.
Pb conc. (ng/m3)
120
Sep. 1995 ∗ Aug. 1996
80
Coarser
PM10
56
47
57
Mean
29.2
14.3
40.5
Median
25.4
8.90
32.6
Max.
93.0
142
170
Min.
4.44
3.17
4.83
Samples
40
0
1992
Finer
1994
1996
1998
2000
2002
2004
Year
FIGURE 1. Average concentration of Pb in finer fractions at
the Lisbon metropolitan area (PM2.5; all stations).
Pb conc. (ng/m3)
200
150
FIGURE 4. Box plots (usual notation) for Pb data (in ng m-3;
from PM10) in Greater Lisbon – Bobadela (top), Póvoa de
Santa Iria and S. João da Talha (bottom) – 1999 to 2002.
Vertical lines separate spring/summer from autumn/winter.
100
50
0
1992
1994
1996
1998
2000
2002
2004
Figure 5 gives box-and-whisker plots for lead (data
from 1999 and 2000) in Lisbon and Setúbal – the most
Pb-laden conurbations according to the 1993 survey.
Representation is customary: error bars denote the 5th
and 95th percentiles, and outer values may be viewed
as outliers at the corresponding significance level. Box
sizes evidence a minimal scatter of data, and similar
features between the two areas. As mentioned before,
the Lisbon-Setúbal corridor did stand for a worst-case
scenario through the 1990s, so the present results point
to a sharp reduction in the lead content of ambient air,
as seen through its concentration in particulate matter.
This is good news, of course, even though the whole
issue of lead dispersion in the environment is still far
from being accounted for. Studies held for an urbanwaste incinerator in the same general area are showing
that about 15 % of the children born at Lisbon's main
maternity ward have significant levels of lead in their
blood [24]. The relatively high residence time of lead
in their mothers' bodies are most certainly showing up
through the newborn babies, despite an abatement in
atmospheric concentrations. Generally speaking, it all
looks as if mankind will have many years ahead to get
rid of its own lead, even if stringent measures are taken
on environmental grounds.
Year
FIGURE 2. Average concentration of Pb in coarser fractions
at the Lisbon metropolitan area (PM2.5-10; all stations).
Pb conc. (ng/m3)
80
60
40
20
0
1992
1994
1996
1998
2000
2002
2004
Year
FIGURE 3. Average concentration of Pb in both fractions at
the Lisbon metropolitan area (PM10; all stations).
458
ACKNOWLEDGEMENTS
Pb Concentration (ng/m3)
400
The authors are indebted to Isabel Dionísio, Orlando
Oliveira and Rute Pinheiro for work assistance, and to
IAEA, EDP, IDAD and ValorSul for financial support.
360
320
280
REFERENCES
240
200
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160
120
80
40
0
FBob FSJT FPie FPal FFar CBob CSjt CPie CPal CFar
FIGURE 5. Lead concentrations in fine (F) and coarse (C)
particulates for Lisbon – Bobadela (Bob), S. João da Talha
(SJT) and Piedade (Pie) – and Setúbal – Palmela (Pal) and
Faralhão (Far) – monitoring stations (1999-2000).
CONCLUSIONS
Airborne-Pb levels over an urban-industrial corridor
within metropolitan Lisbon were sharply reduced to
some (few) tenfold nanograms per cubic meter of air,
as seen through lead concentrations in both inhalable
(PM10) and respirable (PM2.5) fractions of suspended
particulate matter. Individual, 24-h measurements are
far below the current guideline value of 500 ng m-3, set
by the European Union in 1999.
The present situation is very different from the early
1990s, when average figures were in the range of a few
hundreds of ng m-3, and individual measurements were
not seldom found to spike beyond the now-legislated
threshold. Moreover, lead data seems rather stabilised
since around 2000, seemingly fluctuating close to the
rural-background (with no noticeable traffic density),
past-decade levels observed back in 1995-1996. Both
findings should be clearly attributed to the widespread
use of unleaded gasolines, tentatively introduced and
fully enforced in 1990 and 1999, respectively.
Judging from the abatement of lead concentrations in
the arguably most-polluted conurbations in Portugal –
Lisbon and Setúbal metropolitan areas – the whole
country might as well be fairly within the limits of
compliance with the EU regulations in this matter.
Some seasonal variation is also apparent in the data:
lead emissions tend to be slightly higher in autumn and
winter, as generally expected though. Prevailing trends
for lead in the atmospheric environment, alas, have yet
to be mirrored by important public-health indicators,
such as newborn-blood levels from prenatal exposure.
459