Yaacov Mamane

Transport of Saharan dust across the eastern Mediterranean

Earlier studies estimated the production of natural dust from the Saharan desert to be between 200 and 260 million ton per year. These figures were based solely on the westward transport of Saharan dust. In this study estimates on the dust transport to the eastern Mediterranean are provided. The data were obtained from several studies concerned with dust storms in Israel including: ground and airborne particle mass concentration, vertical profiles, dust storm trajectories, particle deposition and the climatology of dust storms in the eastern Mediterranean. A simple two dimensional transport model applied to the above data yields a production rate of 70 million tons of Saharan dust y−1 which are transported eastward. About one third of this amount reaches the east Mediterranean coast located at a distance of 2000 km from the Saharan source.

Intercomparison of methods for sampling and analysis of atmospheric mercury species

An intercomparison for sampling and analysis of atmospheric mercury species was held in Tuscany, June 1998. Methods for sampling and analysis of total gaseous mercury (TGM), reactive gaseous mercury (RGM) and total particulate mercury (TPM) were used in parallel sampling over a period of 4 days. The results show that the different methods employed for TGM compared well whereas RGM and TPM showed a somewhat higher variability. Measurement results of RGM and TPM improved over the time period indicating that activities at the sampling site during set-up and initial sampling affected the results. Especially the TPM measurement results were affected. Additional parallel sampling was performed for two of the TPM methods under more controlled conditions which yielded more comparable results.

Nitrate formation on sea-salt and mineral particles—A single particle approach

Heterogeneous reactions of NO2 and HNO3 at sub-ppm levels with individual sea-salt and mineral particles were investigated. Particles deposited on filters and on electron microscope grids placed in a Teflon reaction chamber, were exposed to NO2 or HNO3 under controlled conditions. Experiments were carried out under dark conditions and were repeated under u.v. radiation (solar simulation). Nitrates formed on the particles were determined by bulk and individual particle analyses. Individual sea-salt and mineral particles were observed in a transmission electron microscope for the presence of nitrate on the particle surface. The formation of nitrates on sea-salt particles under dark conditions, was in the range of 0.1–3.3 mg NO3− g−1 NaCl. Higher values were obtained for mineral particles: 0.2–8.2 mg NO3− g−1 aerosol ([NO2] =0.18 and 0.54 ppm; [HNO3] = 0.04 ppm; exposure time 1–7 days; relative humidity = 70%). The formation of nitrates on sea-salt particles increased from 3.0 to 16.1 mg NO3− g− NaCl when u.v. radiation was added. Mineral particles did not show a significant increase in nitrate formation under u.v. radiation. Microscopy showed that about 50% of the soil particles reacted with NO2 and HNO3 to form mixed nitrate particles. Almost all sea-salt particles (above 95%) reacted with both gases, although the reaction was not complete and took place only on the particle surface. Application of electron microscopy and a specific microspot technique provided direct evidence for the formation of nitrate on sea-salt and mineral particles exposed to NO2 and HNO3.

Atmospheric mercury distribution in Northern Europe and in the Mediterranean region

Mercury species in air have been measured at five sites in Northwest Europe and at five coastal sites in the Mediterranean region during measurements at four seasons. Observed concentrations of total gaseous mercury (TGM), total particulate mercury (TPM) and reactive gaseous mercury (RGM) were generally slightly higher in the Mediterranean region than in Northwest Europe. Incoming clean Atlantic air seems to be enriched in TGM in comparison to air in Scandinavia. Trajectory analysis of events where high concentrations of TPM simultaneously were observed at sites in North Europe indicate source areas in Central Europe and provide evidence of transport of mercury on particles on a regional scale.

Aerosol composition of urban and desert origin in the eastern Mediterranean

Aerosol samples were collected in Tel-Aviv, Israel, during two different atmospheric situations, clear days and dust storms, and were analyzed for shape, size distribution, elemental composition, and presence of sulfate in individual particles. Results of two cases are presented in this paper. In both cases about 80% of the 0.2 to 2.0 µm particles contained sulfate. On the clear day over 50% of the total were pure sulfates while 27% were mixed sulfates; on the dusty day 63% were mixed sulfates — desert particles coated with sulfate — and only 20% were pure sulfates. The sulfate content of the desert particles was fairly high, on the order of 0.1 g sulfate g−1 of desert particles. A possible explanation of this phenomenon may be heterogeneous nucleation of SO2 on the surfaces of insoluble desert particles during their passage over the Mediterranean.

Dynamic processes of mercury over the Mediterranean region: results from the Mediterranean Atmospheric Mercury Cycle System (MAMCS) project

The Mediterranean Atmospheric Mercury Cycle System (MAMCS) project was performed between 1998 and 2000 and involved the collaboration of universities and research institutes from Europe, Israel and Turkey. The main goal of MAMCS was to investigate dynamic processes affecting the cycle of mercury in the Mediterranean atmosphere by combining ad hoc field measurements and modelling tasks. To study the fate of Hg in the Mediterranean Basin an updated emission inventory was compiled for Europe and the countries bordering the Mediterranean Sea. Models were developed to describe the individual atmospheric processes which influence the chemical and physical characteristics of atmospheric Hg, and these were coupled to meteorological models to examine the dispersion and deposition of Hg species in the Mediterranean Basin. One intercomparison and four two-week measurement campaigns were carried out over a three-year period. The work presented here describes the results in general terms but focuses on the areas where definite conclusions were unforthcoming and thus highlights those aspects where, in spite of advances made in the understanding of Hg cycling, further work is necessary in order to be able to predict confidently Hg and Hg compound concentration fields and deposition patterns.

Evaluation of Computer-Controlled Scanning Electron Microscopy Applied to an Ambient Urban Aerosol Sample

Concerns about the environmental and public health effects of particulate matter (PM) have stimulated interest in analytical techniques capable of measuring the size and chemical composition of individual aerosol particles. Computer-controlled scanning electron microscopy (CCSEM) coupled with energy-dispersive X-ray analysis (EDX) allows automated analysis of particle size, chemistry, and particle classification. In combination with manual SEM and bulk analytical techniques such as X-ray fluorescence, CCSEM can be a valuable tool for characterizing individual ambient particles and determining sources of ambient PM. The goal of this study was to examine several issues related to the quality and validity of CCSEM data. These included the stability of unattended CCSEM for multihour runs, the number of particles that must be analyzed in order to yield representative results, and errors associated with CCSEM. CCSEM was applied to the analysis of a 24 h ambient particle sample collected in Baltimore, MD. The coarse-fraction sample (PM10-2.5) was collected with a dichotomous sampler on a polycarbonate filter. A total of 2819 particles in 78 randomly selected fields of view were analyzed by CCSEM during an unattended 8 h run. Particle diameter, aspect ratio, particle location, X-ray counts for 20 elements, and digital images of each particle and its field of view were stored. The average number of particles per field (N/F), average particle diameter (Dave), average mass loading per field (Mave), and average particle composition were calculated for subsets of the data and compared against results for the full data set in order to assess the stability of the CCSEM analysis over time and the number of particles needed to obtain representative results. These comparisons demonstrated excellent stability of CCSEM over the 8 h run. Physical properties (represented by N/F, Dave, and Mave) of the sample were well characterized by analyzing approximately 360 particles. Chemical properties of the sample (average elemental composition and major chemical class abundances) converged to within a few percent of their final values after analyzing about 1000 particles. However, for many purposes several hundred particles may provide adequate characterization. Convergence of minor class abundances was limited by statistical fluctuations as the number of particles populating a class became very small. Manual review of the CCSEM data identified errors associated with CCSEM due to missed particles, overlapping particles, contrast artifacts, sizing errors, and heterogeneous particles. Most errors could be corrected or eliminated during manual off-line review of the data or avoided by maintaining a proper particle loading on the filter.

Heterogeneous reactions of minerals with sulfur and nitrogen oxides

Abstract The heterogeneous reactions of SO 2 and NO 2 at sub ppm levels with mineral particles, such as soil and cement, were investigated. These reactions were studied to understand the role of mineral particles in the formation of sulfates and nitrates. Experiments were carried out in a static reaction chamber made of Teflon, where particles are deposited on filters and on electron microscope grids. After exposure to SO 2 or NO 2 , individual mineral particles were studied for their sulfate or nitrate content using electron microscopy techniques. In parallel, sulfates and nitrates were also determined by bulk methods applied to the filter samples. Scanning electron microscopy has also been used for the comparison of mineral particles before and after exposure to SO 2 . Results obtained both in bulk and individual particle analyses showed clearly that minerals reacted with sulfur and nitrogen oxides to form sulfates and nitrates, respectively. The formation of sulfate on minerals was in the range of 25–150 mg SO 4 2− g −1 mineral ([SO 2 ] = 0.86 ppm; exposure time 1–5 days; relative humidity (RH) = 85% and various aerosol mass loading). Lower values were obtained for the formation of nitrate, 0.9–4.5 mg NO 3 − g −1 mineral ([NO 2 ] = 0.18 ppm; exposure time 1–5 days, RH = 60%). Application of electron microscopy and microspot techniques to the same samples showed that minerals reacted with SO 2 or NO 2 to form a layer of sulfate or nitrate on the mineral surfaces. Not all the minerals had reacted. For the conditions given above 20–40% of the minerals (0.5–5.0 μm) reacted with SO 2 , and 60–70% of them reacted with NO 2 . Microscopy provided direct evidence on the heterogeneous reaction of sulfur and nitrogen oxides with minerals.

On the nature of nitrate particles in a coastal urban area

Abstract Application of micro spot and electron microscopy techniques to individual particles in a coastal urban site revealed the following: 1. (a) sulfate particles, some of them mixed, dominated the sub-μm (0.3–0.8 μm) size range; 2. (b) nitrates were found mostly in the μm size range, in the form of NaNO3. The latter was verified by X-ray analysis of individual nitrates. Apparently the NaNO3 particles were formed through heterogeneous reaction of gaseous HNO3 with sea salt particles.

Comparison and evaluation of several mobile-source and line-source models in Israel

This study compares several transportation-related air quality models. Two line-source models were used: Caline4 (California Department of Transportation) and Hiway2 (US Environmental Protection Agency). Two mobile-source models, Mobile5b (US Environmental Protection Agency) and COPERT3 (European Environment Agency), along with real-world emission factors were used and evaluated as well. Model predictions of NOx concentrations were compared to measured values at two sites in Israel, differing by fleet composition and physical layout (‘at-grade’ and a ‘cut/depressed’ road sections). The process indicated that emission factors generated by COPERT3 are the most appropriate for free flowing traffic situations in Israel. Predictions by both line-source models were similar when applied to ‘at-grade’ road sections. When applied to ‘cut/depressed’ sections, Hiway2 better predicted concentrations during unstable conditions, while Caline4 better predicted concentrations during stable conditions and peak concentrations.