CHARACTERIZING AIR PARTICULATE MATTER COMPOSITION AND SOURCES IN LISBON, PORTUGAL
S.M. Almeida1*, M.C. Freitas 1, C. Repolho1, I. Dionísio1, H.M. Dung1, A. Caseiro2, C. Alves2, C.A. Pio2, A.M.G. Pacheco3 1
2
Instituto Tecnológico e Nuclear, Reactor, E.N. 10, 2686-953 Sacavém, Portugal
CESAM, Departamento de Ambiente e Ordenamento, Universidade de Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal
3
CERENA-IST, Technical University of Lisbon, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
Contact details of the corresponding author:* Susana Marta Almeida Instituto Tecnológico e Nuclear (ITN), Reactor, E.N. 10, 2686-953 Sacavém, Portugal E-mail:
[email protected] Fax: + 351 219941039 Tel: + 351 219946124
Abstract Ambient aerosols adversely affect human health, visibility and climate. Accurate analyses of the physico-chemical properties of the particles and the identification of sources of particulate matter and its precursors are necessary for developing control strategies. The goal of this research is to determine trends and sources of particulates in the centre of Lisbon by using speciated particulate matter data and back-trajectory analyses. Results showed that in 2007, the annual PM2.5 concentration exceeded the World Health Organization recommended levels. PM2.5 diurnal variability and the ratio between weekdays and weekends concentrations indicated that traffic contributed highly for air quality. Air backtrajectory analysis showed that maritime air mass transport had a significant role on air quality in Lisbon promoting the decrease of anthropogenic aerosol concentrations. Introduction Epidemiological studies have consistently shown an association between Air Particulate Matter (APM) pollution and the number of deaths from cancer and cardiovascular and respiratory diseases1,2. There are also evidences linking particles and increases in hospital admissions for respiratory2-5 and cardiovascular diseases5,6. Epidemiological studies have shown that ambient fine particles (PM2.5) are the main responsible for these associations1. The project “Atmospheric Aerosol Impacts on Human Health” focuses on the chemical characterization of PM2.5 aerosols with the aim of: 1) analysing the health risks associated with aerosols exposure and 2) understanding how the aerosol’s chemical composition contributes to those health risks. The study of
the associations between both the sources contribution and the health impact aims at introducing specific abatement strategies in industrial processes, automobile circulation and city planning, which could decrease the levels of APM and, consequently, decrease the impacts on human health. Results presented in this paper were obtained within this project. Higher number of rhinitis episodes was observed in April months (123 children) and in August months (27 cases) in a Lisbon basic school population. The present paper aims at determining trends and sources of particulate matter for these two months. Experimental Sampling During 2007, PM2.5 was collected on a daily basis in the centre of Lisbon (38º44’N; 9º8’W). Sampling was done with a Partisol sampler operating at a flow rate of 16 l.min-1. Aerosol samples were collected on Teflon® filters with 47 mm diameter. Gravimetric Analysis The filter loads were measured by gravimetry using a Mettler Toledo balance with 0.1 µg readability placed in a controlled clean room (class 10,000). The exposed filters were cut into two parts: one was analyzed by Neutron Activation Analysis and the other was analyzed by Ion Exchange Chromatography. Chemical Analysis – Neutron Activation Analysis Element characterization of APM was performed by Neutron Activation Analysis. Each filter half was irradiated in the Portuguese Nuclear Reactor for 57 h, and measured for 4-7 h after 3-7 days and 4 weeks of decay in high purity and high resolution germanium detectors, with an automatic sample changer. A
comparator – 0.1% Au-Al disc – was irradiated and measured for application of the k0 Neutron Activation Analysis8. All measured species in blank filters were very homogeneously distributed; therefore, concentrations were corrected by subtracting the blank filter contents. The Instrumental Neutron Activation Analysis technique has already demonstrated its potential to yield both accurate and precise measurements of APM9, 10. Air mass back trajectories For each starting sample date three days backward trajectories, ending in Lisbon, were calculated with the Hysplit Model11 at 50, 500 and 1000 m height and using the vertical velocity option. According to the backward trajectories, air masses arriving in Lisbon during the sampling campaign were classified into five main groups: M- Maritime air masses – if backward trajectories indicated an ocean origin, without continental contamination, during the previous 3 days; MTMaritime transformed air masses - if backward trajectories indicated an ocean origin, with a final re-circulation through the Iberian Peninsula; SC- South Continental air masses – if backward trajectories indicated an African or Southern Europe origin, N/CC- North/Centre Continental air masses - if backward trajectories indicated an origin in the North or Centre of Europe and CT- Continental transformed air masses - if backward trajectories indicated an European origin with a final re-circulation through the ocean13. Results and Discussion In 2007, PM2.5 annual average mass concentration was 19 g.m-3. This value did not exceed the PM2.5 limit value of 25 g.m-3 defined in the Common
Position (EC) No. 13/2007 of 25 June 2007. However, results showed that students were exposed to PM2.5 concentrations that exceeded the World Health Organization and U.S. Environmental Protection Agency recommended levels of 10 g.m-3 and 15 g.m-3, respectively. The concentration variability along the day allowed an insight within the main source of PM2.512. Hourly PM2.5 concentrations measured in Entrecampos (2 km from the sampling station) - by the Air Quality Monitoring Network from the FIG. 1 111
Portuguese Environmental Agency - showed strong diurnal patterns of the PM2.5 pollution (Figure 1a). PM2.5 exhibited maximum values in the traffic hours as a consequence of exhaust emissions, tires and brake wear and resuspension of dust. The difference between aerosol concentrations measured in weekdays and weekends allowed the evaluation of the contribution of local anthropogenic activities14. Figure 1b showed that PM2.5, NO3, Zn and Sb concentrations were higher during the weekdays. Results, already discussed elsewhere12, showed that these species are associated with vehicles exhaust (NO3-), tires and brake wear and motor oil (Zn and Sb). The lower number of vehicles in August, due to the summer holidays, could explain the lower PM2.5 concentrations registered in this month (15 g.m-3) compared with April (21 g.m-3). PM2.5 levels were mainly due to anthropogenic particles derived from local
FIG. 2 111
sources and long-range transport13. According to Figure 2, the most abundant species (concentrations generally higher than 1 g.m-3) in PM2.5 were SO42-, NH4+, NO3-, Na+, Cl-, Ca2+, K+, Mg2+ and Fe.
18% of the PM2.5 mass was not explained by the measured species. The lack of mass closure (i.e. constituent concentrations not adding up to the gravimetrically measured) was partly due to unmeasured species namely black and organic carbon, which in Lisbon, are mainly associated with traffic13, 15. SO42- and NH4+ - which derive from gas to particle conversion process from SO2 oxidation and NH3 neutralization - contribute to 45% and 17% of PM2.5 mass, respectively. These ions presented a strong correlation (0.97) which indicated that SO42- was mostly present as ammonium sulphate. NO3- represented in average 8% of the PM2.5 mass (Figure 2). FIG. 3 111
Due to the geographical position of Lisbon (on the extreme southwest of Europe) and the dominant western wind regime, influenced by the presence of the semipermanent Azores high-pressure and the Icelandic low-pressure systems over the North Atlantic Ocean, maritime influence was very important for the aerosol characteristics. Figure 3a shows that lower concentrations of SO42-, NH4+, NO3were associated with Maritime trajectories due to the transport of these clean air masses from the Atlantic Ocean. SO42, NH4+, NO3- presented lower concentrations in August (7104, 2528 and 1120 ng.m-3, respectively) than in April (9015, 3749 and 1780 ng.m-3, respectively) due to the more frequent influence of maritime air masses transport to the site. Sea spray ion concentrations (Na+, Cl-, Mg2+) accounted for 7.3 % of the total PM2.5 mass (Figure 2). Figure 3b shows that higher concentrations of Na+, Cl-, Mg2+ were associated with maritime trajectories. However, regardless of air mass origin, the concentrations of these ions are higher in Portuguese coastal areas than in more continental European regions13.
Conclusions PM2.5 composition was investigated in order to identify the main sources for PM2.5 variability during April and August 2007 in the centre of Lisbon. PM2.5 levels were mainly due to anthropogenic constituents, being the ions SO42-, NH4+ and NO3- the most abundant species in PM2.5. The concentration variability along the day and the ratio between weekdays and Sundays showed traffic to be an important source of particles in this area. Air back-trajectory analysis indicated maritime air mass transport as having a significant role on air quality in Lisbon by promoting a decrease of anthropogenic aerosol concentrations. Air pollution abatement strategies as well as public health strategies should focus on traffic and on non-mobile combustion processes emitting sulphur and NOx, which contribute most to the formation of secondary aerosols.
Acknowledgments We gratefully acknowledge FCT by funding the project POCI/AMB/55878/2004 and PPCDT/AMB/55878/2004. References 1. C.A. POPE, R.T. BURNETT, M.J. THUN, E.E. CALLE, D. KREWSKI, K. ITO, G.D. THURSTON, Journal American Medical Association, 287 (2002) 1132. 2. J. SCHWARTZ, Environmental Research, 62 (1993) 7. 3. W. ROEMER, G. HOEK, B. BRUNEKREEF, Am. Rev. Respir. Dis., 147 (1993) 118.
4. C.A. POPE, Arch. Environ Health 46 (1991) 90. 5. R.T. BURNETT, R. DALES, D. KREWSKI, R. VINCENT, T. DANN, J.F. BROOK, American Journal Epidemiology, 142 (1995) 15. 6. J. SCHWARTZ, R. MORRIS, American Journal Epidemiology, 142 (1995) 22. 7. M.I. ASHER, S. MONTEFORT, B. BJÖRKSTÉN, C.K.W. LAI, D.P. STRACHAN, S.K. WEILAND, H. WILLIAMS, The Lancet, 368 (2006) 733. 8. F. DE CORTE. Aggrégé thesis, Gent University, Belgium, 1987. 9. S.M. ALMEIDA, M.A. REIS, M.C. FREITAS, C.A. PIO, Nucl. Instrum. Meth. Phys Research B, 207 (2003) 434. 10. S.M. ALMEIDA, M.C. FREITAS, M.A. REIS, C.A. PIO, J. Radioanal. Nucl. Chem., 257 (2003) 609. 11. R.R. DRAXLER, G.D. HESS, Aust. Meteorol. Mag., 47 (1998) 295. 12. S.M. ALMEIDA, M.M. FARINHA, M.G. VENTURA, C.A. PIO, M.C. FREITAS, M.A. REIS, M.A. TRANCOSO, Water Air Soil Pollut, 179 (2007) 43. 13. S.M. ALMEIDA, C.A. PIO, M.C. FREITAS, M.A. REIS, M.A. TRANCOSO, Atmospheric Environment, 39 (2005) 3127. 14. S.M. ALMEIDA, C.A. PIO, M.C. FREITAS, M.A. REIS, M.A. TRANCOSO, Atmospheric Environment, 40 (2006) 2058. 15. S.M. ALMEIDA, C.A. PIO, M.C. FREITAS, M.A. REIS, M.A. TRANCOSO, Science of the Total Environment, 368 (2006) 663.
Figures' captions
Figure 1. a) Mean hourly levels of PM2.5 in Entrecampos (g.m-3). b) Ratio Weekday/Sunday concentrations for PM2.5 and species associated with vehicles emissions. Figure 2. Average concentration of PM2.5 species (ng.m-3) and its contribution for total mass of PM2.5 (%) Figure 3. SO42-, NH4+ and NO3- (a) and Na+, Cl- and Mg2+ (b) average concentrations discriminated by air mass type (Marit. – Maritime air masses; Marit. Transf. – Maritime Transformed air masses, North/Centre Cont. - North Centre Continental air masses, Cont. Transf. – Continental Transformed air masses, South Cont. – South Continental air masses. Values in ng.m-3.
Weekday/Sunday
00:00 01:00 02:00 03:00 04:00 05:00 06:00 07:00 08:00 09:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00
[PM2.5] (µg.m-3 )
a) 25
23
21
19
17
15
b)
3.0
2.5
2.0
1.5
1.0
0.5
0.0
PM2.5 NO 3 -
Fig. 1
Zn Sb
%PM2.5
70
100000
60
10000
50
1000
40
100
30
10
20
1
10
0.1
0
0.01 PM2.5 Sc
Co
La As Se
Sb Br Cr Zn
Fig. 2
Fe Mg2+ K+ Ca2+ Cl- Na+ NO3 - NH4 + SO4 2-
Concentration (ng.m -3)
Contribution to PM2.5 (%)
Concentration
a) SO42SO42-
NH4+ NH4+
NO3NO 3
North/Centre Cont. 12000 8000 4000
Marit. Transf.
Cont. Transf.
0
Marit.
South Cont.
b) + Na+ Na
Cl-Cl
Mg2+ Mg2+
North/Centre Cont. 1500 1000 500
Marit. Transf.
Cont. Transf.
0
Marit.
South Cont.
Fig. 3
