METODOLOGIE GEOCHIMICHE DI ANALISIDEL PARTICOLATO SOLIDO AERODISPERSOE VALUTAZIONE DEI CONTRIBUTI ANTROPICI E NATURALI

Abstract

The particulate matter is a complex mixture of liquid and solid particles in a suspension. The chemical composition of the particles can be very different depending on the emission sources: anthropogenic (combustion, industrial emissions…) or natural (sea spray, soil re-suspension, biogenic aerosol, forest fires, volcanic ashes, Saharan dust). Different studies have showed that the anthropogenic particulate are formed as a result of low quality of the air, but is important the natural particulate too. Such emissions do not create big pollution problems, because they occur on a small temporal scale. Some particular cases have formerly reported in this regard; for instance, the Saint Helens volcano, erupted in May 1980, caused a worsening in the quality of the air in the United States and in all north-west Pacific Sea, or in another case, the Tambora volcano in Indonesia erupted in April 1815 with an emission of ashes one hundred times greater than the Saint Helens eruption, causing death and famine and a reduction of the solar radiation, which let to very cold winter. The Saharan dust can travel in the air for thousands of miles coming until Italy, Greece or United Kingdom. Therefore, it is important to study the natural and anthropogenic emissions of the particulate matter to reduce the concentrations of aerosol in atmosphere and to protect the human health [Pope, 2000a e b; Harrison, et al., 2004]. The United Nations Economic Commission for Europe (UNECE) showed how important is to define the local and transboundary background levels to reduce the emissions. The aim of this thesis was to adopt a methodology to analysis the particulate matter according to the measures provided in Directive 2008/50/CE [Directive 2008/50/CE, EU Parliament], which explains the necessity of reducing the air pollution to protect ambient and human health with good monitoring and valuation of the quality of the air [UE n. 1600/2002/CE, 22 July 2002]. The researchers of ENEA developed a data processing in order to estimate the importance of some natural sources of emissions in the increasing of the particulate matter, through MINNI project (Modello Integrato Nazionale a supporto della Negoziazione Internazionale sui temi dell’Inquinamento Atmosferico - National Integrated Model to support the international negotiation on atmospheric pollution). The main target of this thesis is to develop an analytical methodology to analyze the chemical composition of the aerosol emitted from different sources in different area in Italy. To do so, different samples of aerosols were obtained on filters and their chemical composition was determined by ICP-MS. The sample preparation for ICP-MS analysis involved the extraction of the inorganic ions in a water solution with ultrasonic [EMEP, 1996]. However, some problems were created with this methodology; for example, the loss of the samples on the filter. For this reason, the sample preparation for ICP-MS involved the dissolution of both the aerosol and the filter. The new analysis protocol was taken place as follows: a low quantity of reagent was used and ensured the complete dissolution of the filter and the aerosol in an acid solution on a hotplate. The acid solutions of HF, HNO3 e H2O2 were used through different steps. The quartz filters showed the best results for ICP-MS analysis, because they provide a low background value during the analysis. Different typologies were also tested: Whatman, Pallflex and SKC. Pallflex® and SKC, however, showed the best results for acid dissolution. On the other side, Teflon filters showed the best results for SEM-EDS analysis, because they allow the collection of an accurate particle size of the aerosol, and they are not made of silica. This is important because they allow to determine the silica particles. Various monitoring and sampling approaches were carried out in different areas of Italy, during 2009 and 2010, to identify the natural contribution of the aerosol in atmosphere. The first approach was tested as part of the MINNI project “determination of PM10 and PM2,5 mass due to natural sources (Saharan dust, sea spray and wind re-suspension of crustal material) and temporary anthropogenic activity (construction sites and agricultural operations)” with ENEA collaboration. The aim of this project was to evaluate the increase of PM in atmosphere during agricultural activity. The sampling area is located in the Po Valley, near Adriatic Sea. It is an area with an elevate concentration of aerosol and with a lot of agricultural area, without farms or industries in a ratio of 30 km Sampling was carried out in 2009, during the main activity of the wheat cycle: wheat threshing (June 2009), plowing (October 2009) and wheat sowing (November 2009). The aerosol emitted during these three agricultural operations was gathered on filters through Marple Impactor. These filters were analyzed by ICP-MS to know the chemical composition of the aerosol and by SEM-EDS to know the morphology of the particles. The comparison of these two methodologies has allowed determining the markers of the natural sources of the particulate matter. The results showed a low contribution of the aerosol emitted from these agricultural operations, because the particles had large size and they fall down rapidly on the ground. The imaging by SEM-EDS showed high amount of organic materials (pollen, spores, molds and bacteria) on the filters in all agricultural activity, which can create serious problem on human health, because their size is very small (less than 2.5 μm). This could be very important for epidemiological studies, especially in people who work with soil. Within the MINNI project, the concentrations of particulate matter analyzed in an area in the south of Italy (Trisaia – Matera), to evaluate the levels of background and the anomalies of PM concentrations during Saharan events and sea spray contributions. Trisaia was chosen as a test site because it is an area near the sea and subjects to Saharan dust in the summer, and also there is no industrial district in the region. For this reasons, it could be a perfect site to analyze the natural contribution of particulate matter. The sampling and analysis methodologies were defined during the 2009, and in the summer 2010 (May and June). Sampling was carried out in Trisaia, which is 4 Km far from the sea and on the border between Basilicata and Calabria. The aerosol was sampled on filters through Andersen Impactor for PM10 and PM2,5 in a time of 23 hours and 30 minutes for all days of the sampling. These filters were analyzed by ICP-MS to know the chemical composition of the aerosol. Moreover, SEM-EDS was performed to know the morphology of the particles. The ICP-MS data showed a negligible presence of pollutants that validate a low anthropogenic contribution and confirmed that the test site is a good site to study the particulate from natural sources. The SEM imaging showed that the major contribution of the aerosol was due to crustal material and sea salt in the fine fraction and in the coarse fraction. In June, the concentrations of PM were higher than in May, because of the Saharan dust event (11 – 19 June 2010). The contribution of sea spray is evident through the high presence of Sodium and salt hydrates. The ICP-MS and SEM results showed a considerable concentration of carbonate by re-suspension of lithologies from the mountains near the test site. The conclusion of this study is that the contribution of sea salt is high in areas near the sea, which can influence the increase of aerosol in atmosphere. Also, the Saharan dust contributes at increasing the aerosol in atmosphere especially in areas in the south of Italy, exceeding the limits allowed by law. Po Valley and Friuli Plain in Italy and Belgian Plain in Europe, are areas with the highest concentration of solid particulate matter in all the world [European Space Agency, 2004]. This implies that those areas do not follow the limits imposed by European Parliament in 2008 [EU Parliament legislative, 2007; EU Parliament directive, 2007]. Aim of this study is the characterization of the particulate matter through direct sampling in atmosphere to define physical properties and source of this particulate. A first campaign was carried out in June-July 2009 in the Po Valley during farming activities of threshing. A second campaign has been carried out in June-September 2009 in the city of Trieste during activity and no activity of the Servola iron foundry. In both campaigns, the aerosol was collected by means of a small aircraft (Cessna 172P), in collaboration with OGS (l’Istituto Nazionale di Oceanografia e Geofisica Sperimentale - Trieste). Particle concentration was measured for five particle sizes (0.5, 1.0, 2.5, 5.0, 10.0 microns) using a laser counter (LIGHTHOUSE HH 3016). The acquisition has been carried out vertically profiling the atmosphere from 150 to 2400 meters. SEM, as well as SEM-XPD analysis on single particles, was carried out with the aim to obtain detailed dimensional and morphological information to define origin, toxicity and the nature of organic matter. An impactor was located in the ram air intake. The collection of the particles was conducted using the direct flux of air. It was assumed that the speed of the aircraft has been maintained steady, this causes the entrance of the ram air in the filter at a constant flow, so it is possible to know the quantity of air passing through Teflon filter. This was possible in the Po Valley, because there is no mountain, but it was impossible in Trieste, because the presence of mountains and of updrafts not allow to maintain a constant velocity. SEM-EDS analysis of the samples of Po Valley showed the presence of particles that are not influenced by agricultural activity. This confirms that the threshing operation not influenced the increase of PM in atmosphere. Instead, in the samples of Trieste SEM-EDS analysis showed a high contribution of carbonate particles, originated from the erosion of the carbonate quarry near the sampling site. The analysis showed also carbon particles, but in a percentage negligible. Despite this, the data showed that the percentage of carbon particles in June is higher than in September, probably the Servola iron foundry is not the only anthropogenic source that increases the carbon concentration in atmosphere. It is important to consider the high impact of the harbor pollution, because there is a big industrial harbor near the city of Trieste. In a last project, the concentration of particulate matter in atmosphere was analyzed by sampling the snow in different period of the winter 2009-2010. The analytical methodologies were defined to characterize the morphological and chemical composition of the particles inside the snow and discriminate the local and transboundary contributions. In literature, a few studies analyzed the aerosol less than 2,5 μm, because it is difficult to sample and analyze aerosols with this size [Brunekreef, et al., 2002]. The snow were analyzed and collected in Ferrara and in Dolomite. It is noted that extreme conditions of snowfall can remove the particulate in atmosphere and create good conditions to collect this pollutant [Loranger, et al., 1996] and hypothesize its source, transport and deposition [Barrie & Vet, 1984; Hautala, et al., 1995]. Chemical analysis might be a good way to know the contamination level in urban area. Despite this, the identification of the sources is difficult, especially for the trace elements that are present both in anthropogenic and natural event. Sample the snowfall was important to understand if it might be considered an indicator to evaluate the anthropogenic impact and/or transboundary of particulate matter. The samples were collected in urban and rural area in Ferrara (Po Valley) and in the Dolomite, and they were analyzed by SEM, IC and ICP-MS. Thanks to this project, the sampling of snow samples allowed to characterize alkaline elements and the particulate matter. This is important, because the soluble particles can interact with biomass and penetrate in groundwater, creating serious environmental problems. Also, the snow melts on the leaves or on the trees and the particulate can be re-suspended creating serious problem on human health. SEM analysis, in collaboration with Birmingham University Department of Geography Earth & Environmental Sciences, showed that the particles are characterized by silica, carbonate, carbon and organic material. Also, ICP-MS data showed high concentration of alkaline elements only in the samples collected near streets (anthropogenic contribution). Chemical and morphological analysis allowed us to know the contamination of the air in urban areas. Despite this, the identification of the particulate matter is not easy, especially for trace elements that are present both in anthropogenic and natural events. This study suggests that there is a direct contamination of the snow from anthropogenic sources (road traffic) and so an important concentration of trace elements near the streets with large number of vehicles passing nearby. The results showed that the snow is interesting to understand the critical level, the contribution of the different sources and the risks for human health and the environmental