Atmospheric Environment (v.40, #30)
Editorial board (i).
Atmospheric ammonia measurement with an ion mobility spectrometer by LaToya Myles; Tilden P. Meyers; Larry Robinson (5745-5752).
An ion mobility spectrometry system was deployed during a field experiment to measure ambient ammonia (NH3). A dual-cell AirSentry ion mobility spectrometer (ASIMS) was utilized to measure ambient NH3 in suburban Tampa, FL from 1 to 16 October 2003. Statistical analysis of half-hourly averaged data showed that the concentration distribution was bimodal. The vicinity of the first mode of the data set had a mean and standard error of 1.4±0.1 ppb, which was ascribed to background levels of NH3, while the mean concentration of the second mode, 3.5±0.1 ppb, probably represented the contribution from local emission sources. Joint frequency distributions of NH3 concentration and 16 wind direction sectors were developed into pollution roses. The largest joint frequency values were from the NNW through NE sectors as well as the SW and SE sectors. Spikes in NH3 concentrations were observed in winds emanating from the N, NNE, S, and NW sectors. A comparison of a cumulative pollution rose and a map of known NH3 emitters in the vicinity of the sampling site showed a direct relationship between winds emanating from the sectors where fertilizer manufacturing facilities were located and high NH3 concentrations.
Keywords: Ion mobility spectrometry; Ammonia; Tampa;
Isoprene and monoterpene emissions from an Inner Mongolia grassland by Jianhui Bai; Bradly Baker; Baosheng Liang; James Greenberg; Alex Guenther (5753-5758).
Terpenoid emissions were measured at a grassland site in Inner Mongolia, China during four campaigns over a 2-year period. Emissions were strongly correlated with light and temperature and the variations could be simulated using a canopy emission model. Substantial seasonal and interannual variations in isoprene emissions were also observed. Area averaged isoprene emissions normalized to standard above-canopy temperature and light conditions (30 °C and 1500 μmol m−2 s−1) ranged from about 50 to 500 μg m−2 h−1. These rates are more than an order of magnitude higher than those previously reported for temperate grasslands but are lower than emission rates observed from ground cover vegetation at higher latitudes. Isoprene emissions from this Inner Mongolia grassland may be dominated by emissions from sedges, e.g. Carex appendiculata. Total monoterpene emissions normalized to a standard temperature of 30 °C were only about 3 μg m−2 h−1 and consisted primarily of carene and limonene with smaller contributions of α-pinene and β-pinene. A model sensitivity study showed that grass and other herbaceous ground cover can contribute >10% of the total isoprene emission from certain regions, such as Inner Mongolia, but are<4% on a global annual scale.
Keywords: Biogenic emissions inventory; Carex; China; Volatile organic compounds (VOCs);
Off-line diagnostic analyses of a three-dimensional PM model using two matrix factorization methods by Jinyou Liang; Ajith Kaduwela; Bruce Jackson; Kemal Gürer; Paul Allen (5759-5767).
Error diagnosis of fine-grid photochemical transport models (CTM) has become a formidable task, which requires thorough understanding of complex microphysical and photochemical processes in the atmosphere as well as scientific computing. In an initial modeling exercise conducted for the California Regional PM10/PM2.5 Air Quality Study (CRPAQS), abnormally high, unrealistic, PM sulfate concentrations were simulated in central California. To aid the error diagnosis, two matrix factorization methods, namely absolute principal component analysis (APCA) and an efficient non-negative matrix factorization method (NMFROC), were used to analyze the relationships among the input and output parameters of a CTM for PM modeling and to apportion the relative importance of individual factors to an abnormal sample. The APCA method corroborated sciences implemented in the PM model, but failed to apportion the relative importance of individual factors to PM sulfate in an abnormal case. On the other hand, the NMFROC method performed well on the apportionment of an abnormally high PM sulfate. The factors produced from the NMFROC method shared common features with the APCA method, but significant differences remain between the two methods, which can be understood from their difference in methodology. Subsequent PM modeling results were shown to validate the results from the NMFROC method.
Keywords: Corroborative analysis tool; Air quality model; Sulfate; San Joaquin Valley;
Formaldehyde measurements in libraries: Comparison between infrared diode laser spectroscopy and a DNPH-derivatization method by B. Hanoune; T. LeBris; L. Allou; C. Marchand; S. Le Calvé (5768-5775).
Formaldehyde concentrations have been measured in the university libraries in Strasbourg (east of France). Infrared diode laser spectroscopy and a conventional DNPH-derivatization method followed by liquid chromatography coupled to UV detection have been used simultaneously for comparison purposes.The formaldehyde concentrations obtained by both the techniques were always in excellent agreement, showing that the infrared diode laser spectroscopy can be used for formaldehyde monitoring in indoor atmosphere, with a time resolution of few minutes.Formaldehyde concentrations were generally found to be in the range 8–33 μg m−3, except for two libraries where concentrations of 82 and 105 μg m−3 have been measured. Using the results obtained by both techniques, the resulting mean formaldehyde level in the investigated libraries was then 33.5±31.2 μg m−3, where the quoted error correspond to the standard deviation.Acetaldehyde and hexanal levels have also been quantified by duplicated measurements in the same libraries by the DNHP-derivatization method. They ranged from 0.0 to 11.3 μg m−3 for acetaldehyde and from 1.0 to 16.7 μg m−3 for hexanal and their mean values were found to be 2.1±3.2 μg m−3 (acetaldehyde) and 4.0±4.4 μg m−3 (hexanal), where the quoted errors correspond to the standard deviation.
Keywords: Formaldehyde; Infrared diode laser spectroscopy; Aldehydes; Libraries; Indoor air; DNPH;
Moss: A powerful tool for dioxin monitoring by Alejo Carballeira; J. Ángel Fernández; Jesús R. Aboal; Carlos Real; Javier A. Couto (5776-5786).
Plants are used as target organisms in most biomonitoring studies of atmospheric deposition of dioxins and furans (PCDD/F) because the most common route of entry of these pollutants into ecosystems is through soils and plants. However, comparison of the results of such studies is difficult because different plant species are used. In the present study we propose the use of mosses as biomonitors of PCDD/F deposition because of their suitable characteristics (absorption of substances from the atmosphere only, large absorbing surface, wide distribution of some species, etc.). We measured the PCDD/F concentrations in tissues of Pseudoscleropodium purum collected in areas far from known sources of pollution and in the surroundings of potential sources of these pollutants (several types of industries, incinerators and burning rubbish dumps). Part of the samples were collected with the aim of monitoring changes in the pollution intensity around some selected sources over time, others were collected to study the spatial gradient of pollution around other sources. Our results indicate that the measurements of the concentration of PCDD/F in the moss tissue allow the detection of strong and weak pollution sources and that these measurements are sensible enough to monitorize changes in the pollution intensity along time, as well as to describe the spatial gradients of pollution created around point sources, and the differences in the relative abundance of isomers (homologue profiles) among different sources. We concluded that mosses are as good biomonitors for PCDD/F as they are for other types of pollutants.
Keywords: Dioxin; Biomonitoring; Pseudoscleropodium purum; Principal component analysis; Homologue profiles;
A comparison of dust properties between China continent and Korea, Japan in East Asia by Xingna Yu; Tiantao Cheng; Jianmin Chen; Yan Liu (5787-5797).
The optical properties of Asian dust were examined from the Aerosol Robotic Network (AERONET) measurements at 10 sites during 2001–2005. A comparison of dust properties was performed between China continent as source regions and Korea, Japan as downwind regions where the dust properties were influenced by long-range transport. Higher aerosol optical thicknesses (AOT) appeared at Chinese sites than Korean and Japanese sites associated with lower Angström exponents (α). The value of α decreased with increasing AOTs, and decreased to zero or negative when the heavy dust events occurred especially in source regions. The aerosol volume size distributions showed a tri-modal structure, one accumulation mode with radius 0.07 μm and two coarse modes with radii 1.3 and 2.9–3.8 μm in source regions, one accumulation mode with radius 0.09 μm and two coarse modes with radii 1.3–2.2 and 2.9–3.8 μm in downwind regions. In view of climate, the single scattering albedo (SSA) at 440, 670, 870 and 1020 nm was used as 0.95 in source regions of China, and in downwind regions such as 0.92 of Korea and 0.95 of Japan. The real parts of refractive index showed a behavior of low sensitivity to wavelengths, 1.51 in source regions of China, and in downwind regions 1.45 of Korea and 1.39 of Japan at the same four wavelengths. The imaginary parts also showed a low sensitivity to wavelengths, with values of 0.0015–0.0044 in source regions and 0.0018–0.0052 in downwind regions at the four wavelengths. The asymmetry factors at the four wavelengths were used as 0.67 over source and downwind regions in climate and radiation models. This difference in dust properties between source regions and downwind regions was mainly attributed to the impacts of dry depositing and wet scavenging during the long-range transport of dust plume.
Keywords: Dust; Optical properties; Dust event; Long-range transport; East Asia;
Improved retrievals of cloud boundaries from MODIS for use in air quality modeling by Keith D. Hutchison; Tatyana Pekker; Solar Smith (5798-5806).
A new approach has been developed at the Center for Space Research (CSR) to determine cloud boundaries from satellite data for use in air quality modeling. The approach combines remotely sensed cloud thickness, obtained from the MODIS cloud optical property products, with cloud base height measurements made at surface weather observing facilities to determine cloud top height. When compared to cloud truth estimates, compiled from measurements made at the Southern Great Plains Atmospheric Radiation Measurement Site in Oklahoma, errors in cloud top height from this new method were found to be significantly smaller than those in the MODIS (MOD06) cloud product. It was also found that relatively small errors in MOD06 cloud top temperatures can be magnified in MOD06 cloud top pressures because the interpolation scheme appears to not adequately consider humidity profiles in the NCEP data used to make these conversions.
Keywords: Cloud boundaries; Cloud top heights; Cloud base heights; MODIS;
Characterizations of resuspended dust in six cities of North China by Pusheng Zhao; Yinchang Feng; Tan Zhu; Jianhui Wu (5807-5814).
Particulate matter is the chief pollutant of urban ambient air in North China, and the contribution of resuspended dust to urban ambient PM10 is very high. Studies on source apportionment for urban ambient particulate matter and resuspended dust were carried out in six north cities (Tianjin, Jinan, Shijiazhuang, Taiyuan, Urumqi and Yinchuan) during 2000 and 2002. About 150 resuspended dust samples were collected in these cities and then resampled PM10 from them in resuspension chamber in the lab. Samples were analyzed by ICP and X-ray fluorescence for 19 elements (Na, Mg, Al, Si, P, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Br, Ba and Pb), ion chromatography for 4 ions (Cl−, NO3−, SO4 2− and NH4 +) and carbon elemental analyzer for TC and OC. Crustal elements and TC are in abundance in resuspended dust. Zn, Cu, and Cr are enriched. According to the results of CMB receptor model, resuspended dust was the greatest source type of ambient PM10 in six cities, and soil, cement and coal combustion were the main contributors to resuspended dust.
Keywords: Resuspended dust; Profiles; Chemical composition; PM10; North China;
Effect of the 1950s large-scale migration for land reclamation on spring dust storms in Northwest China by Wanquan Ta; Zhibao Dong; Caidan Sanzhi (5815-5823).
During the 1950s, China experienced large-scale human migration for the purposes of land reclamation, industrialization, and construction in Northwest China, with a peak of nearly 70 million migrants in 1959 during the Great Leap Forward period. These intense human activities were responsible for the 1950s’ dust storms in Northwest China. Due to large-scale reclamations, the number of spring dust storm days did not show much relationship with the number of spring strong wind days in the Tarim Basin and the Hexi Corridor, but they did correlate with the increase in annual land reclamation areas, with correlation coefficients of 0.82 and 0.88, respectively, in the two regions. Indeed, severe dust storm outbreaks (visibility less than 200 m) in Xinjiang, Gansu and Qinghai provinces in Northwest China were also found to be positively correlated with the number of annual immigrants and the annual increase in cultivated land areas in the period 1953–1968, with coefficients of 0.62 and 0.65, respectively.
Keywords: Large-scale migration; Reclamation; 1950s; Spring dust storm; Northwest China;
Transport to ground of emissions in aircraft wakes. Part II: Effect on NO x concentrations in airport approaches by A. Graham; D.W. Raper (5824-5836).
Predictions as to the transport of aircraft NO x emissions to ground level in the vicinity of an airport are made, taking account of the vortical dynamics of the aircraft wake. A model is used to calculate mean ground-level concentrations. It employs a kinematic approach, harnessing results from dynamical models in the literature. Two aircraft types are considered, a B737-300 (twin turbofan), taken as representative of short-range aircraft, and a B747-400, taken as representative of long-range aircraft. Airport and meteorological parameters are assigned values as holding in the case of Manchester Airport, UK, during a fortnight in May 1999 (prior to the opening of a second runway there). The airport operated at a capacity of about 45 aircraft movements per hour in the peak morning period, with frequencies in the middle of the day being about half this. Aircraft of maximum takeoff weight in excess of 120 tonnes accounted for some 6% of all movements. The simulations predict mean NO x concentrations of maximum 3 μg m−3 at the centre of the runway arising as a result of the vortex-mediated transport (as expressed on conversion of all NO to NO2), with concentrations on the order of 1 μg m−3 arising 0.5 km laterally from the runway.
Keywords: Airport air quality; Aircraft NO x ; Wake vortex; Dispersion model;
Photochemically induced decarboxylation in diesel soot extracts by A. Braun; S. Wirick; A. Kubátová; B.S. Mun; F.E. Huggins (5837-5844).
Aqueous extracts from diesel engine exhaust particulate matter (soot) obtained by hot pressurized water extraction were subject to near-edge X-ray absorption fine structure (NEXAFS) spectroscopy with respect to the carbon K (1 s) absorption edge at a synchrotron radiation source. The highly intense X-ray beam caused a significant decrease of the carboxyl peak intensity at 288 eV, to the benefit of a newly arising carbonate peak at 291.2 eV. The same phenomenon was found in alginic acid when exposed to the same conditions. With knowledge of the molecular structure of alginic acid, we are able to propose a simple photochemical reaction scenario that describes a decay path for carboxyl in soot: the radiolysis of carboxylate into carbonate in diesel soot during irradiation.
Keywords: NEXAFS spectroscopy; Diesel soot extract; Decarboxylation; Photolysis;
Mutagenicity and polycyclic aromatic hydrocarbons associated with extractable organic matter from airborne particles ⩽10 μm in southwest Mexico City by Rafael Villalobos-Pietrini; Omar Amador-Muñoz; Stefan Waliszewski; Leonel Hernández-Mena; Zenaida Munive-Colín; Sandra Gómez-Arroyo; José Luis Bravo-Cabrera; Alejandro Frías-Villegas (5845-5857).
A year-long sampling and analysis of 24 h airborne particles equal to or less than 10 μm (PM10) was conducted in Southwest (SW) Mexico City in 1998. The amount of airborne PM10 and its extractable organic matter (EOM) were highly correlated. The year 1998 was particularly dry with many fires, and higher values of PM10 and EOM were obtained in the fire period (February–May) compared to the without fire period (January, June–December). The indirect-acting mutagenicity (Salmonella typhimurium strain TA98 with mammalian metabolic activation, S9) did not correlate with the monthly concentrations of PM10 and EOM, while the direct-acting mutagenicity (strains TA98 and YG1021, without mammalian metabolic activation) did correlate. The highest monthly mutagenic potency of TA98+S9 and of TA98−S9 were registered in May which correspond to the fire period, while for YG1021 the highest was in December, a without fire month. The highest TA98+S9/TA98−S9 ratios appeared from April to September (with the exception of June), indicating that emission of the direct mutagens occurred in the rest of the year (the coldest months), and December showed the highest mutagenicity of YG1021. The correlation of this mutagenicity with the number of ground-based inversions indicated a greater emissions of nitroarenes in the coldest months emitted mainly by vehicular traffic as shown by the correlation between YG1021 with CO and with NO2. We did not find a correlation in the EOM of the complex mixtures between TA98+S9 and the total concentration of polycyclic aromatic hydrocarbons (PAH) nor between TA98+S9 and specific PAH. The analysis by gas chromatography/mass spectrometry indicated the presence of retene, a PAH found in the fire period and considered a softwood burning marker. The concentrations of fluoranthene and benz[a]anthracene correlated with that of retene and with the burned area; they were the only PAH that presented significant differences between the periods with fire and without fire, showing that these compounds could have a similar origin. Benzo[ghi]perylene, coronene and indeno[1,2,3-cd]pyrene were the most abundant PAH of the 17 analyzed in SW Mexico City, indicating that the main emission source for PAH in the airborne particle phase in this zone were vehicles with the combustion of gasoline and diesel rather than wood burning. The mean concentrations for most PAH were higher during the fire period, except for perylene and coronene, suggesting that the fires were not the emission source for these two last PAH.
Keywords: PM10; PAH; Direct-acting mutagens; Indirect-acting mutagens; Fire period;
Flow reactor studies of the stable carbon isotope composition of secondary particulate organic matter generated by OH-radical-induced reactions of toluene by Satoshi Irei; Lin Huang; Fabrice Collin; Wendy Zhang; Donald Hastie; Jochen Rudolph (5858-5867).
Secondary particulate organic matter (POM) formed in a flow reactor by the OH-radical-induced reactions of toluene was collected on quartz fiber filters, and its stable carbon isotope ratio was analyzed by off-line combustion and subsequent dual-inlet isotope ratio mass spectrometry. The toluene consumption in these experiments ranged from 7% to 29%. The stable carbon isotope composition (δ 13C) of the secondary POM was in the range of −32.2‰ to −32.9‰ (VPDB scale), with some indication for a slight dependence on the extent of toluene consumption. These measured δ 13C values were, on average, 5.8‰ lighter than those of the parent toluene. Those observations are slightly lower than the δ 13C values of the sum of all toluene oxidation products (from −31.6‰ to −32.3‰) that are predicted using the kinetic isotope effect for the reaction of toluene with OH-radical under these reaction conditions and the initial δ 13C of the parent toluene. Therefore, mass balance dictates that the fractionation between gas-phase and particle-phase products is small. On average, the particle-phase products are 0.6‰±0.2‰ lighter than the gas-phase products. This is in agreement with the concept that the initial reaction of toluene with the OH-radical is the slowest step in the reaction sequence resulting in POM formation.
Keywords: Stable carbon isotope; Kinetic isotope effect; Toluene oxidation; Secondary organic aerosols; Aerosol yield;
Long-term trends of greenhouse gases in regional and background events observed during 1998–2004 at Yonagunijima located to the east of the Asian continent by Yukitomo Tsutsumi; Kazumasa Mori; Masaaki Ikegami; Terumasa Tashiro; Kazuhiro Tsuboi (5868-5879).
We performed trend analyses using hourly data of CO, CO2, CH4, and O3 from 1998 to 2004 on Yonagunijima (24°28′N, 123°01′E), which is a small island in south Japan and located close to the Asian continent. The hourly CO concentrations observed were classified as “regional events” or “background events” based on the time scale of the variations. In addition, the hourly mean CO2, CH4, and O3 concentrations observed were also classified as regional or background events based on the CO events. The trends in the regional and background events in the four parameters were analyzed separately.The annual mean CO concentration in the regional event classified above on Yonagunijima was well consistent with the annual coal consumption in China. The annual mean concentrations of all parameters in the regional event were higher than those in the background event. For CO and CO2, the mean growth rates classified as regional events were evidently larger than those classified as background events, and their concentration differences (concentration in the regional event minus that in the background event) have been increasing on Yonagunijima. As the frequency of regional events on Yonagunijima was 44%, the influence of the increase in regional events on the atmospheric environment in East Asia cannot be neglected.
Keywords: Continental outflow; Long-range transport; Regional event; Background event; Trend analyses;
Satellite remote sensing of particulate matter and air quality assessment over global cities by Pawan Gupta; Sundar A. Christopher; Jun Wang; Robert Gehrig; Yc Lee; Naresh Kumar (5880-5892).
Using 1 year of aerosol optical thickness (AOT) retrievals from the MODerate resolution Imaging Spectro-radiometer (MODIS) on board NASA's Terra and Aqua satellite along with ground measurements of PM2.5 mass concentration, we assess particulate matter air quality over different locations across the global urban areas spread over 26 locations in Sydney, Delhi, Hong Kong, New York City and Switzerland. An empirical relationship between AOT and PM2.5 mass is obtained and results show that there is an excellent correlation between the bin-averaged daily mean satellite and ground-based values with a linear correlation coefficient of 0.96. Using meteorological and other ancillary datasets, we assess the effects of wind speed, cloud cover, and mixing height (MH) on particulate matter (PM) air quality and conclude that these data are necessary to further apply satellite data for air quality research. Our study clearly demonstrates that satellite-derived AOT is a good surrogate for monitoring PM air quality over the earth. However, our analysis shows that the PM2.5–AOT relationship strongly depends on aerosol concentrations, ambient relative humidity (RH), fractional cloud cover and height of the mixing layer. Highest correlation between MODIS AOT and PM2.5 mass is found under clear sky conditions with less than 40–50% RH and when atmospheric MH ranges from 100 to 200 m. Future remote sensing sensors such as Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) that have the capability to provide vertical distribution of aerosols will further enhance our ability to monitor and forecast air pollution. This study is among the first to examine the relationship between satellite and ground measurements over several global locations.
Keywords: Aerosols; Satellite remote sensing; Air quality; Mega cities;
Wet deposition and related atmospheric chemistry in the São Paulo metropolis, Brazil. Part 3: Trends in precipitation chemistry during 1983–2003 by Adalgiza Fornaro; Ivano G.R. Gutz (5893-5901).
The metropolitan area of São Paulo (MASP), with 18 million inhabitants, is one of the largest urban areas of the world, with serious environmental problems, including atmospheric pollution. Even though there is an official network monitoring the air quality, it does not include data on the chemical composition of precipitation. However, some research groups have sampled and measured common analytes in rainwater on several sites at MASP during restricted periods. Eventually, available data of pH values and ion concentrations in rainwater since 1983 in the city of São Paulo have been compiled and are, now, discussed in this work, which, besides showing possible trends, gives support for future studies planned in MASP. A decreasing trend of rainwater free acidity in São Paulo occurred along the 2 decades considered. Since 1995, no monthly volume weight mean (VWMm) pH values below 4.5 have been observed which, in part, reflects the gradual decrease in the atmospheric concentrations of the SO2, with annual average of 65 μg m−3 in 1983 and 15 μg m−3 in 2003. Scarce data on sulfate concentration in the rain shows a similar decay from 33±35 μmol L−1 in 1989–1990 to 19±18 μmol L−1 in 2002–2003. Despite the fact that no significant trends can be inferred in the limited nitrate database, for ammonium, high concentrations (47±42 μmol L−1 of NH4 +) have been observed in recent years, indicating the contribution of the NH3 present in the São Paulo's atmosphere to the neutralization of the rain acidity.
Keywords: Acid rain; Historical trend; Nitrate; Sulfate; Megacity;
A review of dispersion modelling and its application to the dispersion of particles: An overview of different dispersion models available by N.S. Holmes; L. Morawska (5902-5928).
This paper provides the first review of the application of atmospheric models for particle dispersion. The different types of dispersion models available, from simple box type models to complex fluid dynamics models are outlined and the suitability of the different approaches to dispersion modelling within different environments, in regards to scale, complexity of the environment and concentration parameters is assessed. Finally, several major commercial and non-commercial particle dispersion packages are reviewed, detailing which processes are included and advantages and limitations of their use to modelling particle dispersion. The models reviewed included: Box models (AURORA, CPB and PBM), Gaussian models (CALINE4, HIWAY2, CAR-FMI, OSPM, CALPUFF, AEROPOL, AERMOD, UK-ADMS and SCREEN3), Lagrangian/Eulerian Models (GRAL, TAPM, ARIA Regional), CFD models (ARIA Local, MISKAM, MICRO-CALGRID) and models which include aerosol dynamics (GATOR, MONO32, UHMA, CIT, AERO, RPM, AEROFOR2, URM-1ATM, MADRID, CALGRID and UNI-AERO).
Metal distribution in road dust samples collected in an urban area close to a petrochemical plant at Gela, Sicily by Emanuela Manno; Daniela Varrica; Gaetano Dongarrà (5929-5941).
Eight samples of road dust were collected from three different localities (industrial, urban, peripheral) of the town of Gela (Italy) to characterize their chemical composition and to assess (a) the influence of the petrochemical plant and the urban traffic on the trace element content in different grain-size fractions of street dust and (b) the solid-phase speciation of the analysed metal using sequential extraction. The samples were sieved into six particle size ranges: 500–250, 250–125, 125–63, 63–40, 40–20 and <20 μm and then analysed for 15 trace elements by ICP-MS. Sequential extraction of metals was performed on each subsample. A principal component analysis was also carried out to define the possible origin of metals in dusts. A comparison was made between the trace metal concentrations in road dust and those in main local outcropping rocks. The obtained results, indicate, that the road dust samples contain non-soil-derived elements, whose primary contributors appear to be vehicular traffic and the nearby petrochemical plant. Traffic appears to be responsible for the high levels of Ba, Cu, Cr, Mo, Pb, Sb and Zn. High concentrations of Ni, V and, partly, Ba and Cr were associated with emissions from the petrochemical plant. With respect to the local background, Sb was the most highly enriched trace element in the road dusts. Results of sequential extraction analysis show that most metals are mainly distributed in the non-residual fractions and particularly in the organic/sulphide and Fe–Mn oxides fractions. They also point to superficial adsorption as an important transfer mechanism of trace metals from their sources to the environment.
Keywords: Air pollution; Heavy metals; Metal speciation; Particulate matter; Roadway dust;