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Review Article Atmospheric Deposition: This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract The atmosphere is a carrier on which some natural and anthropogenic organic and inorganic chemicals are transported, and the wet and dry deposition events are the most important processes that remove those chemicals, depositing it on soil and water.
A wide variety of different collectors were tested to evaluate site-specificity, seasonality and daily variability of settleable particle concentrations. Deposition fluxes of POPs showed spatial and seasonal variations, diagnostic ratios of PAHs on deposited particles, allowed the discrimination between pyrolytic or petrogenic sources.
More and more sophisticated and newly designed deposition samplers have being used for characterization of deposited mercury, demonstrating the importance of rain scavenging and the relatively higher magnitude of Hg deposition from Chinese anthropogenic sources.
Recently biological monitors demonstrated that PAH concentrations in lichens were comparable with concentrations measured in a conventional active sampler in an outdoor environment.
In this review the authors explore the methodological approaches used for the assessment of atmospheric deposition, from the analysis of the sampling methods, the analytical procedures for chemical characterization of pollutants and the main results from the scientific literature.
Introduction Atmospheric deposition is the transfer of atmospheric pollutants dust, particulate matter containing heavy metals, polycyclic aromatic hydrocarbons, dioxins, furans, sulphates, nitrates, etc. The research in atmospheric deposition has increased a great deal over the past years, because of its increasing significant contribution to the explanation of pollution phenomena in many environmental compartments along with the possibility to evaluate the impacts of pollution sources at long and short distance as in fugitive emissions and the possibility to carry out long-term studies aimed at performing health impact assessment on exposed population.
The atmosphere is the carrier on which some natural and anthropogenic organic and inorganic chemicals are transported, and deposition events are the most important processes that remove those chemicals, depositing it on soil and water surfaces. The prominent source of aerosols in the atmosphere, at the global scale, is the dust injected from arid regions, followed by soil and marine erosion and the anthropogenic sources [ 1 ].
Aerosol deposition occurs through three mechanisms depicted in Table 1 [ 23 ]. Mechanisms of aerosol deposition [ 2 — 5 ]. Dry deposition occurs with several mechanisms like turbulent diffusion, sedimentation, Brownian diffusion, interception, inertial forces, electrical migration, thermophoresis, and diffusiophoresis [ 6 ].
Deposition rates are governed by meteorological factors wind velocity, relative humidityparticle characteristics size and shapeand surface characteristics friction velocity, microscale roughness, and temperature [ 7 ]. The samplers used to evaluate atmospheric deposition can be differentiated into various categories depending on which deposition is collected: Wet deposition flux is conventionally calculated using the concentration measured in precipitation samples and the amount of precipitation recorded in the analysis period.
Under the approximation that the concentrations of pollutants in precipitation depend on the concentrations in the air within which precipitation is formed, the scavenging ratio is defined as When the amount of precipitation is expressed asthe wet deposition flux of the pollutant is related to, and by Differences in the wet deposition fluxes of the pollutant between two sites may be due to different atmospheric concentrations and scavenging ratios.
In rainy areas dry deposition can be neglected compared with wet deposition [ 8 ] or does not basically modify the chemical characteristics of the wet deposition but can be the dominant fraction in arid and semiarid regions where intense dust loadings take place [ 9 — 12 ] and it is necessary to separate wet and dry deposition.
Conversely in higher precipitation regime areas, wet deposition reflects long-range transport phenomena, while dry deposition is more linked to local pollution levels [ 14 ] and dominates deposition processes of micropollutants in the highly industrialized areas [ 15 ].
Dry deposition of organic micropollutants polycyclic aromatic hydrocarbons PAHspolychlorobiphenyls PCBspolybromodiphenyl ethers PBDEsand dibenzofurans dominates atmospheric deposition during no raining periods in some polluted areas [ 1617 ].
These aerosols remain in the atmosphere until removed by wet or dry deposition and due to the residence time about a week are responsible for long-range transport of sulphur and nitrogen [ 18 ]. Speciation of deposited particle gives the opportunity to study mass balance of some metals as in the case of mercury in Lake Michigan and Lake Superior, which showed that atmospheric deposition contributes largely to the total annual input of mercury [ 1920 ].
Study of atmospheric bulk deposition of PAHs in an urban area reveals the presence of a plume of highest concentrations in zone with heavy vehicular traffic and favourable topography for the concentration of emitted pollutants, like in the active sampling in air, and also the diagnostic ratio analyses apportioned the major source of emissions [ 21 ].
Due to the extreme versatility of the analytical tools recently developed in the study of the atmospheric deposition, the existence of numerous methodological approaches, there is the necessity in the studying of the state of the art of this new environmental subject. In this review, the authors explore the methodological approaches used for the assessment of atmospheric deposition starting from the analysis of the sampling methods, the analytical procedures for chemical characterization of pollutants, and the main results from the scientific literature, dividing pollutants into four major classes, starting from organics, followed by inorganics metals other than mercury, ionsmercury on which particular focus has been dedicated by researches due to its peculiarityand biomonitors.
Sampling and Analytical Techniques 2. You can use wet-only collectors that are designed to collect only sedimenting wet particles or bulk ones to collect all sedimenting wet and dry particles, depending both on the aim of the study and on the sampling site rural, industrial, or urban areas.
The cylindrical vertical section should be of sufficient height to avoid sampling losses resulting from splashing and the diameter for the opening area and the volume of the collector should be selected, in order to collect all the precipitation for the required sampling duration.
Sampling period ranges from one week to one month. The height of the opening area of the collector shall be at least 1. When the volume reached 2 L, the bottles were immediately transported to the laboratory. Bulk deposition sampler positioned round the borders of an industrial site in Taranto Italy.
Stainless steel buckets were used to collect PAHs bulk deposition in remote, rural village, and urban areas [ 23 ]. Distilled water was added into the buckets before sampling, and the amount of distilled water was determined according to the evaporation and precipitation situation, generally 50 mL in summer and winter, and mL in the other seasons.
About 60 mL glycol was also added into each bucket to avoid freezing of water in winter and to reduce the effects of biodegradation. Alternatively to previous collector, bulk deposition samples can be collected with a stainless steel platter whose diameter and depth were 60—76 cm and 19 cm, respectively [ 2226 ].
The collection of bulk deposition of PAHs was achieved by Li et al. The funnel was placed horizontally, 1. After about 30 days, the inner surfaces of the stainless steel funnels were wiped with precleaned cotton. A passive sampling technique using a funnel-absorber-cartridge device was adopted and validated in the field by Gocht et al.About our Guest Writer: CHERYL LEO is Director at Olive Green, a Singapore based retail outlet distributing eco-friendly products.
She is an environmental enthusiast, and is particularly passionate about issues concerning plastics and petroleum. Towards a systematic understanding of the dynamic fate of polychlorinated biphenyls in indoor, urban and rural environments.
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