PIXE and receptor models applied to remote aerosol source apportionment in Brazil

doi:10.1016/0168-583X(87)90339-9

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms

Volume 22, Issues 1–3, 3 March 1987, Pages 259-263

https://doi.org/10.1016/0168-583X(87)90339-9 Get rights and content

Abstract

We have used PIXE together with receptor modeling for quantiative source apportionment of remote aerosols. The Sao Paulo PIXE system uses an 8 MeV alpha particle beam, and it can detect elements with Z > 11 with a detection limit between 1 and 30 ng m³ . We sampled atmospheric aerosols in six remote sites: Amazon Basin. Atlantic Forest, Arembepe, Fernando de Noronha, Firminopolis and Itaherai. Sampling was performed using stacked filter units, cascade impactors with 6 or 10 stages and linear streakers.

Source apportionment of the coarse mode aerosols was done using three receptor models: chemical mass balance, principal factor analysis and stepwise multiple regression analysis. Three sources of aerosols were quantiatively distinguished: marine aerosols, soil dust and aerosols released by plants. The emission of aerosols by vegetation is very clear for all sampling sites and with all three receptor models. In the Amazon Basin and Atlantic Forest the aerosol released by plants is the major source and accounts for 60–80% of airborne concentrations.

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Polycarbonate filters were analyzed for particulate mass, BCe and elemental composition (Maenhaut et al., 2002). PIXE analysis (Particle Induced X-Ray Emission) were made at University of São Paulo LAMFI (Laboratório de Análise de Materiais por Feixes Iônicos) to determine the concentration of 22 elements (Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Se, Br, Rb, Sr, Zr and Pb) (Artaxo and Orsini, 1987). BCe concentrations were obtained using a light reflectance technique.
Aerosol physical and chemical properties were measured in a forest site in central Amazonia (Cuieiras reservation, 2.61S; 60.21W) during the dry season of 2004 (Aug–Oct). Aerosol light scattering and absorption, mass concentration, elemental composition and size distributions were measured at three tower levels (Ground: 2 m; Canopy: 28 m, and Top: 40 m). For the first time, simultaneous eddy covariance fluxes of fine mode particles and volatile organic compounds (VOC) were measured above the Amazonian forest canopy. Aerosol fluxes were measured by eddy covariance using a Condensation Particle Counter (CPC) and a sonic anemometer. VOC fluxes were measured by disjunct eddy covariance using a Proton Transfer Reaction Mass Spectrometer (PTR-MS). At nighttime, a strong vertical gradient of phosphorus and potassium in the aerosol coarse mode was observed, with higher concentrations at Ground level. This suggests a source of primary biogenic particles below the canopy. Equivalent black carbon measurements indicate the presence of light-absorbing aerosols from biogenic origin. Aerosol number size distributions typically consisted of superimposed Aitken (76 nm) and accumulation modes (144 nm), without clear events of new particle formation. Isoprene and monoterpene fluxes reached respectively 7.4 and 0.82 mg m⁻² s⁻¹ around noon. An average fine particle flux of 0.05 ± 0.10 10⁶ m⁻² s⁻¹ was calculated, denoting an equilibrium between emission and deposition fluxes of fine mode particles at daytime. No significant correlations were found between VOC and fine mode aerosol concentrations or fluxes.
Assessment of atmospheric metallic pollution in the metropolitan region of São Paulo, Brazil, employing Tillandsia usneoides L. as biomonitor
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In many cases, the highest increase in concentration occurred in winter time (Exposure B: June–July/2002), in opposition of a period of lower enrichment in relation to the control sample observed in summer (Exposure C: Nov/2002–Jan/2003). In fact, the concentrations of pollutants in São Paulo, especially PM10, are higher in winter than in summer (Orsini et al., 1984, 1986; Artaxo and Orsini, 1987). For a better understanding of the behavior of the elements analyzed in the plants exposed in the polluted sites, a cluster analysis was applied by using Statistica software and the dendrogram obtained from the data is presented in Fig. 3.
Tillandsia usneoides L. is an epiphytic bromeliad plant able to absorb water and nutrients directly from the air. For this reason this species was selected to carry out a monitoring study of air pollution in the metropolitan region of São Paulo, Brazil. Five consecutive transplantation experiments (8 weeks each) were performed in 10 sites of the city, submitted to different sources of air pollution (industrial, vehicular), using plants collected from an unpolluted area. After exposure, trace metals were analyzed in the plant by instrumental neutron activation analysis. Traffic-related elements such as Zn and Ba presented high concentrations in exposure sites near to heavy traffic avenues (cars, buses and trucks) and may be associated to vehicular sources. For Zn and Co the highest contents were related to industrial zones and can be associated to the presence of anthropogenic emission sources. The rare earth elements, Fe and Rb, probably have soil particles as main source.
Wintertime and summertime São Paulo aerosol source apportionment study
2001, Atmospheric Environment
A detailed aerosol source apportionment study was performed with two sampling campaigns, during wintertime and summertime in the heavily polluted metropolitan area of São Paulo, Brazil. In addition to 12 h fine and coarse mode filter sampling, several real time aerosol and trace gas monitors were used. PM₁₀ was sampled using stacked filter units that collects fine (d<2.5 μm) and coarse (2.5<d<10 μm) particulate matter, providing mass, black carbon (BC) and elemental concentration for each aerosol mode. The concentration of about 20 elements was determined using the particle induce X-ray emission technique. Real time aerosol monitors provided PM₁₀ aerosol mass (TEOM), organic and elemental carbon (Carbon Monitor 5400, R&P) and BC concentration (Aethalometer). A complex system of sources and meteorological conditions modulates the heavy air pollution of the urban area of São Paulo. The boundary layer height and the primary emissions by motor vehicles controls the strong pattern of diurnal cycles obtained for PM₁₀, BC, CO, NO_x, and SO₂. Absolute principal factor analysis results showed a very similar source pattern between winter and summer field campaigns, despite the different locations of the sampling sites of both campaigns, pointing that there are no significant change in the main air pollution sources. The source identified as motor vehicle represented 28% and 24% of the PM_2.5 for winter and summer, respectively. Resuspended soil dust accounted for 25% and 30%. The oil combustion source represented 18% and 21%. Sulfates accounts for 23% and 17% and finally industrial emissions contributed with 5% and 6% of PM_2.5, for winter and summer, respectively. The resuspended soil dust accounted for a large fraction (75–78%) of the coarse mode aerosol mass. Certainly automobile traffic and soil dust are the main air pollution sources in São Paulo. The sampling and analytical procedures applied in this study showed that it is possible to perform a quantitative aerosol source apportionment in a complex urban area such as São Paulo.
Precipitation chemistry in the coast of the Metropolitan Region of Rio de Janeiro, Brazil
2001, Environmental Pollution
Precipitation chemistry was studied in the Metropolitan Region of Rio de Janeiro (MRRJ). This study reveals that rainwater in the MRRJ is affected by emissions of air pollutants and provides essential data for future estimates of regional biogeochemical cycles and the impacts of acid deposition on tropical ecosystems. The volume-weighted mean (VWM) pH was 4.77, varying from 3.50 to 6.85. Sea-salt aerosols were the dominant sources of the Na⁺, Cl⁻ and Mg²⁺. Excess SO₄^2-, Ca²⁺ and K⁺ comprised 82, 91, and 87% of their total VWM concentrations, respectively. There were very strong correlations (r>0.75, P<0.01) for NO₃⁻ and H⁺, NO₃⁻ and excess(exc-)SO₄²⁻, NH₄⁺ and exc-K⁺, and exc-SO₄²⁻ and exc-Ca²⁺, suggesting causal relationships between these ion pairs. The VWM concentrations of all major ions, except H⁺, were higher in the dry season, with dry to wet VWM concentration ratios varying from 1.1 (NH₄⁺) to 4.7 (for total K⁺).
Trace elements in lake sediments measured by the PIXE technique
1999, Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms
Lakes are ecosystems where there is a great potential of metal accumulation in sediments due to their depositional characteristics. Total concentration of trace elements was measured on a 50 cm long sediment core from the Infernão Lake, that is an oxbow lake of the Moji-Guaçu River basin, in the state of São Paulo, Brazil. Dating of the core shows up to 180 yrs old sediment layers. The use of the PIXE technique for elemental analysis avoids the traditional acid digestion procedure common in other techniques. The multielemental characteristic of PIXE allows a simultaneous determination of about 20 elements in the sediment samples, such as, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Rb, Sr, Zr, Ba, and Pb. Average values for the elemental composition were found to be similar to the bulk crustal composition. The lake flooding pattern strongly influences the time series of the elemental profiles. Factor analysis of the elemental variability shows five factors. Two of the factors represent the mineralogical matrix, and others represent the organic component, a factor with lead, and another loaded with chromium. The mineralogical component consists of elements such as, Fe, Al, V, Ti, Mn, Ni, K, Zr, Sr, Cu and Zn. The variability of Si is explained by two distinct factors, because it is influenced by two different sources, aluminum-silicates and quartz, and the effect of inundation are different for each other. The organic matter is strongly associated with calcium, and also bounded with S, Zn, Cu and P. Lead and chromium appears as separated factors, although it is not clear the evidences for their anthropogenic origin. The techniques developed for sample preparation and PIXE analysis was proven as advantageous and provided very good reproducibility and accuracy.
Analysis of atmospheric aerosols by PIXE: the importance of real time and complementary measurements
1999, Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms
Particle-Induced X-ray Emission (PIXE) has been used for more than 30 yr in many urban and background air pollution studies. The technique has certainly contributed to the understanding of source-receptor relationship for aerosol particles as well as to aerosol physics and chemistry. In the last few years, where aerosol issues were strongly linked to global climate change through the relationship between aerosol and atmospheric radiation points to new challenges in atmospheric sciences, where PIXE could play an important role. Also the recognition for the inter-relationship between aerosol and liquid and gas phases in the atmosphere makes important to integrate PIXE aerosol analysis with other complementary measurements. The use of Nephelometers and Aethalometers to measure scattering and absorption of radiation by aerosol particles can be done in parallel with particle filter collection for PIXE analysis. Parallel measurements of trace gases using traditional monitors as well as with new techniques such as Differential Optical Absorption Spectroscopy (DOAS) that can provide concentration of O₃, SO₂, NO₃, NO₂, HCHO, HNO₃, Benzene, Toluene, and Xylene, is also important for both urban and remote aerosol studies. They provide information that allows a much richer interpretation of PIXE data. Recently developed instruments that provide real time aerosol data such as the Tapered Element Oscillating Microbalance (TEOM) PM₁₀ monitor and automatic real time organic and elemental carbon analyzers provide extremely useful data to complement PIXE aerosol analysis. The concentrations of trace elements measured by PIXE comprise only 10–30% of the aerosol mass, leaving the organic aerosol characterization and measurement with an important role. The aerosol source apportionment provided by PIXE analysis can be extended with other aerosol measurements such as scattering and absorption, estimating for example, the radiative impact of each discriminated aerosol source. The aerosol bulk PIXE measurements can be complemented with soluble concentrations provided by Ion Chromatography (IC) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). Recent developments in remote sensing techniques and products also enhance significantly regional aerosol studies. Three-dimensional air mass trajectories should be integrated in aerosol studies for urban and remote areas. The applications of these techniques to study urban aerosols from São Paulo and Santiago de Chile have broadened extensively the scientific scope of these studies.

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PIXE and receptor models applied to remote aerosol source apportionment in Brazil

Abstract

Atmos. Environ.

Atmos. Environ.

Nucl. Instr. and Meth.

Atmos. Environ.

Atmos. Environ.