Jan Cafmeyer

Regional atmospheric aerosol composition and sources in the eastern Transvaal, South Africa, and impact of biomass burning

As part of the Southern Africa Fire-Atmosphere Research Initiative (SAFARI-92), size-fractionated aerosol samples were collected during September–October 1992 at three fixed ground-based sites in the eastern Transvaal, i.e., at two sites within the Kruger National Park (KNP) and at a third site on the Transvaal highveld (about 150 km WSW of the KNP sites), and near a number of prescribed fires in the KNP. The collection devices consisted of stacked filter units, which separate the aerosol into a coarse (2–10 μm equivalent aerodynamic diameter (EAD)) and a fine (<2 μm EAD) size fraction, and of eight-stage cascade impactors, which provide more detailed size fractionation. The samples were analyzed for particulate mass (PM), black carbon (BC), and up to 47 elements. The prescribed fires gave rise to high levels of airborne soil dust, but several species (elements) were particularly enriched in the pyrogenic emissions. This was the case for BC, P, K, Ca, Mn, Zn, Sr, and I in the coarse fraction, and for BC, the halogens (Cl, Br, I), K, Cu, Zn, Rb, Sb, Cs, and Pb (and in the flaming phase also Na and S) in the fine fraction. The aerosol concentrations, compositions, and time trends at the two KNP sites were quite similar, suggesting that regionally representative samples were collected. Receptor modeling calculations, using both absolute principal component analysis and chemical mass balance, indicated that the KNP coarse PM was essentially attributable to mineral dust and sea salt, with average relative apportionments of 75% and 25%, respectively. At the highveld site, mineral dust and sea salt contributed in a 99-to-1 ratio to the coarse PM. In the fine size fraction at all three fixed sites, four components were identified, i.e., mineral dust, sea salt, biomass burning products, and sulfate. The pyrogenic component was the dominant contributor to the atmospheric concentrations of BC, K, Zn, and I, a major source for PM, Cl, Cu, Br, and Cs, but only a minor source for S. About 40% of the fine PM was, on the average, attributed to the pyrogenic particles, and about one third of it to the sulfate component. Relation of the time trends of the various components with three-dimensional air mass back trajectories indicated that elevated levels of pyrogenic products were mostly found in air masses arriving from the north. The levels of the sulfate component tended to be higher at the highveld site than at the two KNP sites, and this component was generally associated with continental air. It was concluded that the major contribution to this fine sulfate came from fossil fuel burning and various industrial activities on the Transvaal highveld.

Saharan dust in Brazil and Suriname during the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA)- Cooperative LBA Regional Experiment (CLAIRE) in March 1998

Advection of Saharan dust was observed via chemical and optical measurements during March 1998 in Brazil and Suriname during the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA)-Cooperative LBA Airborne Regional Experiment (CLAIRE)-98 experiment. In Brazil the dust outbreak produced an increase of a factor of 3 in the daily mean mass concentration (up to 26±7 μg m−3) of particles smaller than 10 μm equivalent aerodynamic diameter (EAD), and in the daily mean aerosol particle scattering coefficient σs (up to 26±8 Mm−1 STP, ambient humidity). Background levels of aerosol scattering (ambient) were σs ∼ 10 Mm−1. The effect of dust advection was evident for all major crustal elements (Al, Si, Ca, Ti, Mn, and Fe), as well as the sea-salt elements (Na, Cl, and S), as the dust layer was transported at low altitude (below 800 hPa). Coarse P and organic carbon (OC) concentrations were not influenced by the occurrence of dust, and were mainly emitted by the rain forest. The dry scattering mass efficiency of dust (particles smaller than 10 μm EAD) was estimated to be between 0.65 (±0.06) and 0.89 (±0.08) m2 g−1. Airborne profiles of aerosol scattering showed two distinct types of vertical structure in the dust layer over Suriname, either vertically uniform (15, 26 March), or plume-like (25 March). Dust layers extended generally up to 700 hPa, while scattering layers occasionally encountered at higher altitudes resulted from smoke emitted by biomass burning in Venezuela and Colombia. Observations in South America were supported by measurements in Israel and Tenerife (Canary Islands), where the dust outbreaks were also detected.

Biomass burning in Southern Africa: individual particle characterization of atmospheric aerosols and savanna fire samples

Ambient atmospheric aerosols and savanna fireparticulate emission samples from southern Africa werecharacterised in terms of particle classes and theirnumber abundance by electron probe X-ray microanalysis(EPXMA). About ten particle classes were identifiedfor each sample. The major classes werealuminosilicates and sea salts for ambient coarse(2–10 μm equivalent aerodynamic diameter (EAD))samples, and K-S and S-only particles for ambient fine(<2 μm EAD) samples. The K-S particles are oneof the major products of biomass burning. The EPXMAresults were found to be consistent with the resultsfrom bulk analyses on a sample by sample basis. Forsavanna fire fine samples, quantitative EPXMA revealedthat many particles had a composition of simple saltssuch as KCl. Some particles had a deviatingcomposition in the sense that more ionic species wereinvolved in sustaining the balance between cations andanions, and they were composite or mixed salts.Because of extensive processing during the atmospherictransport, the composition of the K-S particles in theambient samples was different from K2SO4,and such particles were enriched with S. The finepyrogenic KCl particles and the fine sea-saltparticles were much depleted in chlorine.

Particle-induced x-ray emission (PIXE) analysis of biological materials: Precision, accuracy and application to cancer tissues

Abstract An autopsy kidney, a human serum sample and NBS bovine liver were analyzed by both PIXE and instrumental neutron activation analysis (INAA). Several target preparation procedures were investigated. The reproducibility of the PIXE analysis, as determined by analyzing up to 20 targets from the same material, was of the order of 10% or better. For most elements a good agreement was obtained between PIXE and INAA, indicating that PIXE can yield data which are accurate to within 10%. The PIXE technique was also applied to cancerous and normal tissue sections of the same organ of patients, showing renal cell and other types of carcinoma. Substantial differences were often observed between the trace element concentration patterns of the cancerous and normal sections.

Carbonaceous aerosol characterization in the Amazon basin, Brazil: novel dicarboxylic acids and related compounds

Abstract High-resolution capillary gas chromatography (GC) and GC/mass spectrometry (MS) were employed for the quantitative determination of dichloromethane-extractable organic compounds in total and size-fractionated aerosol samples which were collected in the Amazon basin, Brazil, during the wet season, as part of the LBA–CLAIRE-98 experiment. Special emphasis was placed on the characterization and identification of several novel unknown dicarboxylic acids and related oxidative degradation products. This class of acidic products was enriched in the fine size fraction, suggesting that they were secondary organic aerosol products formed by gas-to-particle conversion. Some of the unknowns contributed more to the class of dicarboxylic acids than the major known compound, nonadioic acid (azelaic acid). The same unknowns were also observed in urban aerosol samples collected on hot summer days in Gent, Belgium. For the characterization and structure elucidation of the unknowns, various types of derivatizations and fractionation by solid-phase extraction were employed in combination with GC/MS. Four unknowns were identified. The most abundant were two derivatives of glutaric acid, 3-isopropyl pentanedioic acid and 3-acetyl pentanedioic acid. The other two identified unknowns were another oxo homologue, 3-acetyl hexanedioic acid, and, interestingly, 3-carboxy heptanedioic acid. To our knowledge, the occurrence of these four compounds in atmospheric aerosols has not yet been reported. The biogenic precursors of the novel identified compounds could not be pinpointed, but most likely include monoterpenes and fatty acids.

Influence of sampling artefacts on measured PM, OC, and EC levels in Carbonaceous aerosols in an urban area

Sampling of particulate matter (PM) with filter media is subject to the influence of positive and negative artefacts. The complexity of these measurements derives from the use of different instrumentation, face velocities, and filter types. Carbonaceous compounds are one of the main PM chemical components affected by these artefacts. In this study, two main types of artefacts were evaluated at an urban site in Ghent (Belgium) during the summer period: those related to the sampling procedure (high- or low-volume samplers) and those related to the adsorption and/or volatilization of carbonaceous species. For their measurement, two high-volume (PM10 and PM2.5) samplers with single quartz fiber filters and two low-volume PM2.5 samplers (one of them coupled to an annular diffusion denuder) with double quartz fiber filters (front and backup) were used. PM2.5 mass concentrations measured by means of the low-volume sampler (front filter) were, on average, 31% higher than those registered with the high-volume sampler. PM2.5 mass concentrations registered with the low-volume sampler coupled to the diffusion denuder represented 88% of the PM2.5 mass collected with the undenuded low-volume sampler. Similar values for organic carbon (OC) were recorded for the high- and low-volume samplers. Front filter OC levels for the denuded samples represented 66% of the front filter OC mass on the undenuded samples. Using the backup filter OC data to apply a correction to the front filter data as suggested by Mader et al. (2003) only marginally reduced the discrepancy between the undenuded and denuded OC data, indicating that such correction does not result in consistent OC data for an urban area in Western Europe during summer.

Physical and chemical characteristics of aerosols over the Negev Desert (Israel) during summer 1996

Sde Boker, in the Negev Desert of Israel (30°51′N, 34°47′E; 470 m above sea level (asl), is a long-term station to investigate anthropogenic and natural aerosols in the eastern Mediterranean in the framework of the Aerosol, Radiation and Chemistry Experiment (ARACHNE). Ground-level measurements of physical and chemical properties of aerosols and supporting trace gases were performed during an intensive campaign in summer 1996 (ARACHNE-96). Fine non sea salt (nss)-SO42− averaged 8±3 μg m−3 and fine black carbon averaged 1.4±0.5 μg m−3, comparable to values observed off the east coast of the United States. Optical parameters relevant for radiative forcing calculations were determined. The backscatter ratio for ARACHNE-96 was β = 0.13±0.01. The mass absorption efficiency for fine black carbon (αa,BCEf) was estimated as 8.9±1.3 m2 g−1 at 550 nm, while the mass scattering efficiency for fine nss-SO42− (αs,nss-SO42−f) was 7.4±2.0 m2 g−1. The average dry single-scattering albedo, ω0 characterizing polluted conditions was 0.89, whereas during “clean” periods ω0 was 0.94. The direct radiative effect of the pollution aerosols is estimated to be cooling. At low altitudes (below 800 hPa), the area was generally impacted by polluted air masses traveling over the Balkan region, Greece, and Turkey. Additional pollution was often added to these air masses along the Israeli Mediterranean coast, where population and industrial centers are concentrated. At higher altitudes (700 and 500 hPa), air masses came either from eastern Europe or from North Africa (Algerian or Egyptian deserts). The combination of measurements of SO2, CO, CN (condensation nuclei), and accumulation mode particles allowed to characterize the air masses impacting the site in terms of a mixture of local and long-range transported pollution. In particular, the lack of correlation between SO2 and nss-SO42− indicates that the conversion of regional SO2 into the particulate phase is not an efficient process in summer and that aged pollution dominates the accumulation mode particle concentrations.

Long-term atmospheric aerosol study at urban and rural sites in Belgium using multi-elemental analysis by particle-induced x-ray emission spectrometry and short-irradiation instrumental neutron activation analysis

The Ghent PM10 stacked filter unit (SFU) sampler was used to collect size-fractionated atmospheric aerosol samples, first at an urban residential site in Ghent, Belgium, and subsequently at a rural site (Waasmunster, about half way between the cities of Ghent and Antwerp). The samplings at Ghent took place in 1993–94 (over a 14 month period) and a total of 118 daily SFU samples were collected. At Waasmunster, 142 daily SFU samples were taken in 1994–95 (over a 16 month period). All samples were analyzed for the particulate mass, black carbon, and up to 29 elements. The elements were measured by particle-induced x-ray emission spectrometry (PIXE) and short-irradiation instrumental neutron activation analysis (INAA). The data for common elements measured by both techniques were compared. This permitted an assessment of the magnitude of the particle size effect for the lighter elements in PIXE. The data sets were subjected to receptor modeling with absolute principal component analysis, and relationships between the intensities of the components (i.e. the component scores) and various meteorological variables were examined. The anthropogenic and crustal components were consistently negatively correlated with wind speed. Overall, the aerosol concentrations, compositions, sources and source contributions to the particulate mass were remarkably similar for the urban and rural sites.

Interrelationships between aerosol characteristics and light scattering during late winter in an Eastern Mediterranean arid environment

An intensive field campaign involving measurement of various aerosol physical, chemical, and radiative properties was conducted at Sde Boker (also written as Sede Boqer) in the Negev Desert of Israel, from 18 February to 15 March 1997. Nephelometer measurements gave average background scattering coefficient values of about 25 Mm−1 at 550 nm wavelength, but strong dust events caused the value of this parameter to rise up to about 800 Mm−1. Backscattering fractions did not depend on aerosol loading and generally fell in the range of 0.1 to 0.25, comparable to values reported for marine and Arctic environments. Chemical analysis of the aerosol revealed that in the coarse size range (2–10 μm equivalent aerodynamic diameter (EAD)), calcium (Ca) was by far the most abundant element followed by silicon (Si), both of which are indicators for mineral dust. In the fine size fraction (<2 μm EAD), sulfur (S) generally was the dominant element, except during high dust episodes when Ca and Si were again the most abundant. Furthermore, fine black carbon (BC) correlates with S, suggesting that they may have originated from the same sources or source regions. An indication of the short-term effect of aerosol loading on radiative forcing was provided by measurements of global and diffuse solar radiation, which showed that during high-turbidity periods (strong dust events), almost all of the solar radiation reaching the area is scattered or absorbed.

Chemical composition of atmospheric aerosol in the European subarctic: Contribution of the Kola Peninsula smelter areas, central Europe, and the Arctic Ocean

An 18-month set of concentration data of various elements in fine (diameter D <2.5 μm) and coarse (2.5 μm<D<15 μm) particles is presented. Measurements were done at Sevettijarvi, ∼60 km WNW of Nikel, a large pollution source on the Kola Peninsula, Russia. The concentrations in aerosol arriving from the Norwegian Sea and the Arctic Ocean are very close to the values observed at more remote Arctic sites. In air from the Kola Peninsula, approximately one third of the samples, concentrations of some trace elements were ∼2 orders of magnitude above the background concentrations. The elements most clearly transported in the pollution plumes from Kola Peninsula were Cd, Ni, Cu, V, Pb, As, Fe, and Co. Penner et al. [1993] presented a method for estimating black carbon (BC) emissions by comparing BC/SO2 (S) close to the sources and used a ratio 0.6 for the former USSR. We found that this ratio was <0.1 in the clearest pollution plumes from Kola peninsula. The ratio of the chemical mass to the gravimetric mass of the aerosol samples was ∼80% both for the fine and coarse particle filters, regardless of the source area. Comparison of the aerosol concentrations with the concentrations of elements in snow showed that the deposition was proportional to the aerosol exposure. The contribution of Kola Peninsula to the deposition is high, ∼80% for Ni, Cu, and Co and somewhat lower for other anthropogenic elements.