Atmospheric Environment (v.35, #4)
Fine particle measurements at two background sites in Korea between 1996 and 1997 by Jong Hoon Lee; Yong Pyo Kim; Kil-Choo Moon; Hui-Kang Kim; Chong Bum Lee (635-643).
Five intensive field measurements were carried out at two background sites in Korea; Kosan and Kangwha during spring, fall, and winters of 1996 and 1997 to investigate the characteristics of long-range transport of air pollutants in northeastern Asia. Fine particles (PM2.5) were collected by low-volume samplers and the concentrations of major ions, organic and elemental carbons, and nitric acid were quantified. The concentrations of anthropogenic species in PM2.5 measured at both sites were generally higher than those at other background areas, Nagano, Japan and San Nicolas Is., USA due to continental outflow of air pollutants, but lower than those at an urban background site, Qingdao, China. The major components of PM2.5 were sulfate, organic carbon (OC), and ammonium for Kosan and sulfate, OC, ammonium, and nitrate for Kangwha. The major fractions of sulfate at both sites are non-sea-salts (nss) sulfate. Based on the relationship among major anthropogenic species, analysis of the nss sulfate to total nitrate molar ratios, and backward air parcel trajectories, it was found that fine particles measured at both sites during the measurement periods are mainly coming from China. At Kosan, the concentrations of anthropogenic species were higher when air parcels were coming from southern China than when air parcels were from northern China. At Kangwha, however, the differences of the concentrations were not statistically significant since most air parcels were from northern China and local effects are prominent.
Keywords: PM2.5; Ammonium to nss sulfate ratio; Nss sulfate to nitrate ratio; Long-range transport; Northeastern Asia;
Chemical characteristics of cloud water over the Japan Sea and the Northwestern Pacific Ocean near the central part of Japan: airborne measurements by Koichi Watanabe; Yutaka Ishizaka; Chisato Takenaka (645-655).
Cloud water was collected by aircraft over the Japan Sea and the Northwestern Pacific Ocean during the winter and early spring seasons. The concentrations of major ions in the cloud water were higher at cloud bases than at cloud tops. The equivalents based ratio of Na+/nssSO4 2− and NO3 −/nssSO4 2− at cloud bases was higher than that at cloud tops, whereas the nssCa2+/nssSO4 2− ratio was higher at cloud tops. The concentrations of nssSO4 2− were higher than those of NO3 − over the Japan Sea. The ratio of NO3 −/nssSO4 2− in the cloud water over the Pacific Ocean was higher than that over the Japan Sea. Especially, when the winter monsoon wind pressure pattern collapsed, the concentrations of NO3 − were much higher than those of nssSO4 2−. The concentrations of peroxides in the cloud water ranged from below the detection limit to 6.2 μM, and were much lower than those in the fog water near the summit of Mt. Norikura during the summer season. Most of the samples showed the condition (NH4 ++nssCa2+)<(NO3 −+nssSO4 2−), which implies insufficient amounts of bases to neutralize the acids. Chloride loss in the cloud water was observed, and this may be caused by the deposition of HCl gas to the sea surface.
Keywords: Transport; Non-sea-salt sulfate; Nitrate; Non-sea-salt calcium; Peroxides;
Characteristics of PM2.5 carbonaceous aerosol in the Sihwa industrial area, Korea by Seung S. Park; Young J. Kim; Kochy Fung (657-665).
In order to investigate the characteristics of carbonaceous fine aerosols, PM2.5 particulate samples were collected in the Sihwa industrial complex area between February 1998 and 1999 and in Seoul between 31 May and 9 June 1999, respectively. The carbonaceous species were analyzed by the selective thermal manganese dioxide oxidation (TMO) method. In Sihwa, average OC and EC concentrations for the entire data set were measured to be 9.8 and 1.8 μg m−3, respectively. The OC concentrations were higher than those measured in other urban environments. The EC concentrations were lower than those of other urban environments. The OC/EC ratio measured at the Sihwa area was higher than those at other urban and rural environments. Backward trajectories of sampled air masses were performed to find out the sources of those higher OC/EC levels. Enrichment in the organic compounds during winter periods can be explained by the combination of primary local emissions from the industrial complex area and long-range transport of organic species from outside the Sihwa area. High OC values in June resulted from primary anthropogenic emissions and secondary organic aerosol formation rather than the atmospheric transport of organic compounds from the outside. In urban area of Seoul, the OC and EC concentrations in PM2.5 during the summer were higher than those measured at other urban atmospheres. OC/EC ratios obtained in Seoul were lower than Sihwa. It can be concluded that carbonaceous species in Seoul were mainly emitted from primary anthropogenic sources.
Keywords: OC–EC ratio; Secondary organic carbon; Backward trajectory; Long-range transport; Thermal manganese dioxide oxidation;
Characterization of atmospheric air pollutants at two sites in northern Kyushu, Japan – chemical form, and chemical reaction by Takaaki Shimohara; Okihiro Oishi; Akira Utsunomiya; Hitoshi Mukai; Shiro Hatakeyama; Jang Eun-Suk; Itsushi Uno; Kentaro Murano (667-681).
Airborne gaseous and particulate matter in winter was measured over for 37 days in January and December 1997 at 2 sampling sites in northern Kyushu, Japan. One sampling site, Goto Island (an isolated island in the East China Sea), was about 200 km southwest of the other sampling site, Dazaifu city. In winter, acidic sulfates generated over the East Asian continent were transported to northwest Kyushu, to places such as Goto Island and the inland Kyushu area, and high sulfate concentrations were observed at the 2 sampling sites when strong NW winds blew. Acidity around Goto was mainly influenced by particulate NH4HSO4. The concentrations of NH3 at Goto Island were lower than at Dazaifu city. The difference in NH3 levels at the 2 sampling sites plays an important role in the chemical forms and sizes of the particulate matter. Nitrates at Goto Island were mostly present as NaNO3 and Ca(NO3)2 in coarse-size particles. During the process of long-range transport of air pollutants from the Asian continent to Goto, gaseous HNO3 was produced by a photochemical reactions of nitrogen oxides in the atmosphere, and particulate NaNO3 and gaseous HCl were formed by a chlorine-loss reaction between NaCl and gaseous HNO3. When strong NW winds blew, acidic sulfates together with some of the NaNO3 and/or Ca(NO3)2 and some of gaseous HCl and HNO3, which exist in the sea to the west of Kyushu and Goto Island, were transported to inland Kyushu such as Dazaifu city. During the process of transport, most of the acidic sulfates and acidic gases were mixed with regional air pollutants such as chlorides and nitrates existing around Dazaifu city, and neutralized forming (NH4)2SO4, NH4Cl and NH4NO3 in an environment of excess NH3. Therefore, the main chemical forms of NO3 − at Dazaifu city varied day-by-day from fine-sized NH4NO3 to coarse-sized NaNO3 and/or Ca(NO3)2. The appearance of NO3 − in coarse-size particles at Dazaifu city was due to the transport of NO3 − from around the sea to the west of Kyushu.
Keywords: Acidic aerosols; Sulfate; Nitrate; Winter monsoon; Long-range transport model; Chlorine-loss reaction;
Internal boundary layer structure under sea-breeze conditions in Hong Kong by Heping Liu; Johnny C.L Chan; Andrew Y.S Cheng (683-692).
A three-dimensional atmospheric model is used for modelling the airflow pattern and internal boundary layer (IBL) development over the Hong Kong region that comprises hilly terrain and complex coastline. Observations used to verify the model are drawn from 32 meteorological stations and a ground-based lidar system. It is found that the modelled results are in good agreement with the observed airflow field and IBL development. Due to the interaction of complex terrain and sea-breeze circulations, several confluence zones of wind fields are found in different locations, depending on the background wind velocity and the differential-heating rate between land and sea. Subsequently, these kinds of wind field patterns give rise to a three-dimensional dome-shaped IBL distribution that forms an impediment to air-pollutant dispersion outside of the layer.
Keywords: Three-dimensional atmospheric model; Complex terrain in Hong Kong; Airflow field; Internal boundary layer height; Lidar measurements;
Study of size distribution of atmospheric aerosol at Agra by R.S. Parmar; G.S. Satsangi; M. Kumari; A. Lakhani; S.S. Srivastava; S. Prakash (693-702).
Measurements on size distribution of atmospheric aerosol were made at Dayalbagh, Agra during July to September 1998. A 4-stage cascade particle sampler (CPS - 105) which fractionates particles in sizes ranging between 0.7 and >10.9 μm, was used. Samples were collected on Whatman 41 filters. The filters were analyzed for the major water-soluble ions. The anions (F, Cl, NO3 and SO4) were analyzed by Dionex DX-500 ion chromatograph while atomic absorption and colorimetric techniques were used for the analysis of cations (Na, K, Ca and Mg) and NH4, respectively. The average mass of aerosol was found to be 131.6 μg m−3 and aerosol composition was found to be influenced by terrigeneous sources. The mass size distribution of total aerosol and the ions NH4, Cl, NO3, K, Ca, Mg, SO4 and Na was bimodal while that of F was unimodal. SO4, F, K and NH4 dominated in the fine mode while Ca, Mg, Cl and NO3 were in abundance in coarse fraction. Na was found in both coarse as well as fine mode. Coarse mode SO4 and NO3 have been ascribed to contribution from re-suspension of soil and formation by heterogeneous oxidation on soil derived particles. Preponderance of K in fine mode is attributed to emissions from vegetation and from burning of plant materials. Ca, Mg, Cl and NO3 are largely soil derived and hence dominate in coarse fraction. Equivalent ratios of NH4/(SO4+NO3) were calculated for both fine and coarse aerosols. The coarse mode ratio varied between 0.7 and 1.4 while in fine mode it ranged between 1.4 and 1.9. It shows that aerosol is basic, the basicity of coarse mode is due to higher concentration of soil-derived alkaline components while the basicity in fine mode is due to neutralization of acidity by NH3.
Keywords: Aerosol; Mass size distribution; Coarse and fine particles; Sources;
Sub-region (district) and sector level SO2 and NO x emissions for India: assessment of inventories and mitigation flexibility by A. Garg; P.R. Shukla; S. Bhattacharya; V.K. Dadhwal (703-713).
Sub-regional and sector level distribution of SO2 and NO x emissions inventories for India have been estimated for all the 466 Indian districts using base data for years 1990 and 1995. Although, national level emissions provide general guidelines for assessing mitigation alternatives, but significant regional and sectoral variability exist in Indian emissions. Districts reasonably capture this variability to a fine grid as 80% of these districts are smaller than 1°×1° resolution with 60% being smaller than even 1/2°×1/2°. Moreover, districts in India have well-established administrative and institutional mechanisms that would be useful for implementing and monitoring measures. District level emission estimates thus offer a finer regional scale inventory covering the combined interests of the scientific community and policy makers. The inventory assessment methodology adopted is similar to that prescribed by the Intergovernmental Panel on Climate Change (IPCC) for greenhouse gas (GHG) emissions. The sectoral decomposition at district level includes emissions from fossil fuel combustion, non-energy emissions from industrial activities and agriculture. Total SO2 and NO x emissions from India were 3542 and 2636 Gg, respectively (1990) and 4638 and 3462 Gg (1995) growing at annual rate of around 5.5%. The sectoral composition of SO2 emissions indicates a predominance of electric power generation sector (46%). Power and transport sector emissions equally dominate NO x emissions contributing nearly 30% each. However, majority of power plants are situated in predominantly rural districts while the latter are concentrated in large urban centers. Mitigation efforts for transport sector NO x emissions would therefore be higher. The district level analysis indicates diverse spatial distribution with the top 5% emitting districts contributing 46.5 and 33.3% of total national SO2 and NO x emissions, respectively. This skewed emission pattern, with a few districts, sectors and point sources emitting significant SO2 and NO x , offers mitigation flexibility to policy makers for cost-effective mitigation.
Keywords: Emissions inventory; SO2 emissions; NO x emissions; Emissions mitigation;
Contributions to CO concentrations from biomass burning and traffic during haze episodes in Singapore by P. Mukherjee; S. Viswanathan (715-725).
Prediction of ambient carbon monoxide (CO) due to haze in the presence of transportation sources at a busy expressway site in Singapore was made using street Canyon and Gaussian line source modules of a regional-scale Indic Airviro dispersion model for the haze episodes that occurred in the years 1994 and 1997. The fleet average emission factors for each vehicle category were estimated from US EPA MOBILE 5 A guidelines as a function of speed, vehicle deterioration rates and model years. One hour CO concentrations during the non-haze period for the year 1995 were first simulated and compared with measured readings to test the accuracy of the proposed approach. The calibrated model was then used to compute hourly CO values for the 1994 and 1997 haze episodes. The difference between the modeled CO values with and without haze provided CO contribution due to haze. An analysis of CO values estimated through modeling with experimental measurements made during haze periods confirmed this unique approach to establish concentration of CO due to haze in the presence of transportation sources.
Keywords: Biomass burning; Carbon monoxide; Haze; Traffic pollution;
Transport of SO2 and aerosol over the Yellow sea by Byung-Gon Kim; Jin-Seok Han; Soon-Ung Park (727-737).
Aircraft measurements of air pollutants were made to investigate the characteristic features of long-range transport of sulfur compounds over the Yellow Sea for the periods of 26–27 April and 7–10 November in 1998, and 9–11 April and 19 June in 1999, together with aerosol measurements at the Taean background station in Korea. The overall mean concentrations of SO2, O3 and aerosol number in the boundary layer for the observation period ranged 0.1–7.4 ppb 32.1–64.1 ppb and 1.0–143.6 cm−3, respectively. It was found that the air mass over the Yellow Sea had a character of both the polluted continental air and clean background air, and the sulfur transport was mainly confined in the atmospheric boundary layer. The median of SO2 concentration within the boundary layer was about 0.1–2.2 ppb. However, on 8 November, 1998, the mean concentrations of SO2 and aerosol number increased up to 7.4 ppb and 109.5 cm−3, respectively, in the boundary layer, whereas O3 concentration decreased remarkably. This enhanced SO2 concentration occurred in low level westerly air stream from China to Korea. Aerosol analyses at the downstream site of Taean in Korea showed 2–3 times higher sulfate concentration than that of other sampling days, indicating a significant amount of SO2 conversion to non sea-salt sulfate during the long-range transport.
Keywords: Long-range transport; Aircraft measurement; SO2; Sulfate; Ozone; Aerosol;
Chemical characteristics of principal PM2.5 species in Chongju, South Korea by Hak Sung Lee; Byung-Wook Kang (739-746).
Fine particles were collected over four seasons from October 1995 to August 1996 to evaluate the chemical characteristics of principal PM2.5 components in Chongju, South Korea. The annual mean concentrations of PM2.5 (d p⩽2.5 μm), sulfate, nitrate, ammonium, elemental carbon (EC) and organic carbon (OC) were 44.2, 8.22, 3.63, 2.84, 4.44 and 4.99 μg m−3, respectively. The sum of the species measured from this study accounted for 50–62% of the PM2.5 mass. Sulfate was the most abundant species and constituted 13–23% of the PM2.5 mass. The EC and OC accounted for 17–28% of PM2.5. The correlation between OC and EC was strong, and the annual mean ratio of OC/EC was 1.12, suggesting that OC measured in the Chongju area may be emitted directly in particulate form as a primary aerosol.
Keywords: PM2.5 (d p⩽2.5 μm); SO4 2−; NO3 −; NH4 +; Elemental carbon (EC); Organic carbon (OC); Urban area; South Korea;
Characterization of the winter atmospheric aerosols in Kyoto and Seoul using PIXE, EAS and IC by Chang-Jin Ma; Mikio Kasahara; Susumu Tohno; Kyung-Chul Hwang (747-752).
Characteristics of atmospheric aerosols in Kyoto, Japan and Seoul, Korea were investigated using particle-induced X-ray emission (PIXE), elemental analysis system (EAS) and ion chromatograph (IC). Atmospheric aerosols were collected into fine and coarse fractions using a two-stage filter pack sampler in Kyoto and Seoul in winter of 1998. PIXE was applied to analyze the middle and heavy elements with atomic number greater than 14 (Si), and EAS was applied to analyze the light elements such as H, C and N. The total mass concentration in Seoul was about two times higher than in Kyoto and the concentration of Ca, Si, and Ti that are mainly originated from soil were remarkably higher in Seoul. During an Asian dust storm event, the concentration of soil components increased dramatically and amounted to about 15 times higher than average concentration. The fine/coarse ratios of NH4 +, NO3 −, and SO4 2− were extremely high in both sites. The fact that nearly 70% of fine particles in both Kyoto and Seoul consist of the light elements (N, C, and H) suggests the importance of light elements measurement. Good mass closure for fine particles with light element data was achieved.
Keywords: Light element; PIXE; Element analysis system; Mass closure; Asian dust storm;
Volatile organic compounds in the air of Izmir, Turkey by Aysen Muezzinoglu; Mustafa Odabasi; Levent Onat (753-760).
A sampling program was conducted to determine the ambient VOC levels in the city of Izmir, Turkey during daytime and overnight periods between mid-August and mid-September 1998. Sampling sites were selected at high-density traffic roads and junctions far from stationary VOC sources. Samples were analyzed for benzene, toluene, m, p-xylene and o-xylene (BTX), alkylbenzenes (ethylbenzene, 1,3,5-trimethylbenzene, 1,2,4-trimethylbenzene), n-hexane and, n-heptane. Results were compared with similar data from other cities around the world and for probable health dangers and sources of the compounds. Results of this study indicated that Izmir has rather high ambient BTX concentrations compared to many polluted cities in the world. Toluene was the most abundant VOC in Izmir air and was followed by xylenes, benzene and alkylbenzenes, respectively. All were strongly dependent on the expected daily variations of traffic flow in the city. The concentrations of other VOCs correlated well with benzene concentration at most sampling sites, excluding Gumuldur station indicating that ambient VOC levels were mainly affected by motor vehicle emissions. The toluene-to-benzene ratios for urban and non-urban sites were in good agreement with previously reported values, indicating a good relationship between the motor vehicle emissions and ambient VOC levels.
Keywords: VOCs in urban air; BTX in urban air; Alkyl benzenes in urban air; Hexane and heptane in urban air; Air quality in Izmir;
Estimation of atmospheric inorganic water-soluble particulate matter in Muharraq Island, Bahrain, (Arabian Gulf), by ion chromatography by Ahmed Y Ali-Mohamed; Hussain A.N Ali (761-768).
Inorganic particulate matter was sampled weekly during the period, from March to August of 1996 at eight different sites on Muharraq Island at height of ∼8 m above the ground level. Muharraq is the second most populated of the islands in the country (after the Bahrain island), but in terms of population per square kilometer, it is the most densely populated. Deposited aerosols were chemically analysed by ion chromatography and a comparison was made between these sites. The results were in good correlation with the meteorological and surface features of Bahrain.
Keywords: Dry deposition; Ion chromatography; Cl−; SO4 2−; NO3 − anions; Na+; Ca+ cations; Muharraq; Bahrain;
The content and contributions of deposited aeolian organic matter in a dry land ecosystem of the Negev Desert, Israel by E Zaady; Z.Y Offer; M Shachak (769-776).
The northern Negev desert in Israel has a mosaic of two types of plant community patches. One is dominated by vascular plants (shrub patches) and the other by a nonvascular crust community (crust patches) consisting of cyanobacteria, bacteria, algae, mosses and lichens. The crust patches are sources of soil material and sediment – laden runoff water while the shrub patches are the sinks and function as ‘islands of fertility’ in the desert environment. Accumulation of resources is often a limiting factor in this ecosystem. The aim of this study was to investigate the contribution of high nutrient organic residues that are readily decomposable, to the aeolian deposition on the crust patches. During the five years of the study, three dominant groups were found in the organic matter: plant material, insect and snail residue (feces). The average accumulation of the aeolian deposition of the organic matter showed significant spatial and temporal differences. Similar quantities were found on the north and the south-facing slopes of the watershed with a minimum in the wadi. A significant difference in average accumulated organic matter for the five years was found. The maximum was for the third year (1995) and the minimum for the fifth year (1997). This may be due to the variations in the annual rainfall amount. The results showed that the origin of most of the organic matter content is from native sources. The highest and most significant amount was registered during the spring season, which is the flowering season in the northern Negev. This may explain the high quantity of plant material obtained and the great amounts of insect and snail (feces) residue that were also found during this season. Since the crust patches serve as a source of water and nutrients in this ecosystem, the organic residues that are of high nutrient quality and readily decomposable, contribute to the productivity of the shrub patches and thus of the overall ecosystem.
Keywords: Aeolian deposition; Organic matter; Arid landscape;
Trace gas variations at Cape Point, South Africa, during May 1997 following a regional biomass burning episode by E.-G Brunke; C Labuschagne; H.E Scheel (777-786).
During the continuous monitoring of atmospheric parameters at the station Cape Point (34°S, 18°E), a smoke plume originating from a controlled fire of 30-yr-old fynbos was observed on 6 May 1997. For this episode, which was associated with a nocturnal inversion and offshore airflow, atmospheric parameters (solar radiation and meteorological data) were considered and the levels of various trace gases compared with those measured at Cape Point in maritime air. Concentration maxima in the morning of 6 May for CO2, CO, CH4 and O3 amounted to 370.3 ppm, 491 ppb, 1730 ppb and 47 ppb, respectively, whilst the mixing ratios of several halocarbons (F-11, F-12, F-113, CCl4 and CH3CCl3) remained at background levels. In the case of CO, the maritime background level for this period was exceeded by a factor of 9.8. Differences in ozone levels of up to 5 ppb between air intakes at 4 and 30 m above the station (located at 230 m above sea level) indicated stratification of the air advected to Cape Point during the plume event. Aerosols within the smoke plume caused the signal of global solar radiation and UV–A to be attenuated from 52.4 to 13.0 mW cm−2 and from 2.3 to 1.3 mW cm−2, respectively, 5 h after the trace gases had reached their maxima. Emission ratios (ERs) calculated for CO and CH4 relative to CO2 mixing ratios amounted to 0.042 and 0.0040, respectively, representing one of the first results for fires involving fynbos. The CO ER is somewhat lower than those given in the literature for African savanna fires (average ER=0.048), whilst for CH4 the ER falls within the range of ERs reported for the flaming (0.0030) and smouldering phases (0.0055) of savanna fires. Non-methane hydrocarbon (NMHC) data obtained from a grab sample collected during the plume event were compared to background levels. The highest ERs (ΔNMHC/ΔCH4) have been obtained for the C2–C3 hydrocarbons (e.g. ethene at 229.3 ppt ppb−1), whilst the C4–C7 hydrocarbons were characterised by the lowest ERs (e.g. n-hexane at 1.0 and n-pentane at 0.8 ppt ppb−1).
Keywords: Carbon monoxide; Methane; Ozone; Emission ratios; Biomass burning;
Polar and non-polar volatile organic compounds (VOCs) in urban Algiers and saharian sites of Algeria by Noureddine Yassaa; Brahim Youcef Meklati; Enzo Brancaleoni; Massimiliano Frattoni; Paolo Ciccioli (787-801).
For the first time, polar and non-polar organic compounds from C4 to C20 have been identified and quantified in one urban and two saharan sites located in Algeria. They were collected on adsorption traps filled with graphitic carbons and analyzed by high-resolution gas chromatography–mass spectrometry after thermal desorption. More than 190 compounds released by man-made and biogenic sources or formed in air by degradation of photochemical smog precursors were identified in the city center of Algiers. Some of them were never reported before. During our determinations, high levels of pollution characterized the city. Transport of anthropogenic pollutants together with some biogenic emission from date palm trees was mainly responsible for the levels of VOCs measured in Melika oasis located at the entrance of the Sahara desert. Background tropospheric levels of VOCs were instead detected in Bouchene sandy site of the Sahara desert where no biogenic sources were present.
Keywords: Volatile organic compounds (VOCs); Aerometric concentrations; Urban and remote areas; Algiers city; Sahara desert; GC–MS.;
Dry atmospheric inputs of trace metals at the Mediterranean coast of Israel (SE Mediterranean): sources and fluxes by Barak Herut; Malcolm Nimmo; Angela Medway; Roy Chester; Michael D Krom (803-813).
This study presents the first detailed data on aerosol concentrations of trace metals (Cd, Pb, Cu, Zn, Cr, Mn, Fe and Al) at the SE Mediterranean coast of Israel, and assesses their sources and fluxes. Aerosol samples were collected at two sampling stations (Tel-Shikmona and Maagan Michael) along the coast between 1994 and 1997. Two broad categories of aerosol trace metal sources were defined; anthropogenic (Cd, Cu, Pb and Zn) and naturally derived elements (Al, Fe, Mn and Cr). The extent of the anthropogenic contribution was estimated by the degree of enrichment of these elements compared to the average crustal composition (EFcrust). High values (median >100) were calculated for Cd, Pb and Zn, minor values for Cu and relatively low values (<10) for Fe, Mn and Cr. The crustal-derived elements exhibited a statistically significant seasonal pattern of higher concentrations during spring and autumn (e.g. Al concentrations in some cases during these periods were observed to be in excess of 1500 ng m−3). In the eastern Mediterranean basin crustal-dominated elements are enriched by 2–3 times while others (Cd and Pb) are comparable to the northwestern Mediterranean. The Pb : Cd ratios of ∼150 are higher than in coastal European sites (60–116) or emission materials (∼50). It is speculated that these differences are attributed mainly to the mixing of crustal material with local and European emissions. At present, it is impossible to quantify the latter two fractions. Back trajectory analysis and the subsequent categorization of two main aerosol populations, ‘European’ and ‘North Africa–Arabian’, exhibited a significantly different geochemical imprint on the aerosol chemical composition. ‘European’-derived air masses indicated significantly higher EFcrust values for Cd and Pb due to the greater anthropogenic character of the aerosol population, with a dilution by crustal material of this population leading to comparatively lower EFcrust values associated with the North African–Arabian air masses.
Keywords: Trace metals; Aerosol; Atmosphere; Fluxes; Mediterranean; Pollution; Sahara;