In the last decades, few days a week, several city centres in Italyare closed at vehicular traffic in order to limit the presence of particulate matter, often exceeding the limits set by law [1,2]. The particulate matter have an impact on human health [3,4], in the cultural heritage and natural environment deterioration [5,6]. Many studies have been the carried out in air monitoring in urban areas while the targeted surveys to assess the impact on air quality of snow dispersion for ski activities are rare. Thanks to the Autonomous Province of Trento it has been possible to sample the snowpack in some ski areas inItalyand thanks to stratigraphic profiles it has been possible to observe variations of the chemical composition over time. Natural contribution is strictly related to winds and currents movement, for this reason a deep knowledge of these factors can help in the determination of the prevalent trajectories during the year [7,8]. During a penetrometeric and stratigraphic profile on Presena glacier, the main nivo-meteorological features, air temperature and temperature inside the different layers of the snowpack have been measured. Some snow samples has been collected and analyzed by SEM-EDS, ICP-MS and IC. These qualitative and quantitative analyses allow to obtain chemical and mineralogical composition to define the emitting source.
The study of particulate matter in the snow is not common and few studies are related to the campaigns carried out in Antarctica. Most of the scientific works in Europe verifies the impact of large communication structures on the quality of the snow. This analysis assesses the contributions of local impact on air quality but also verifying the contributions of transboundary aerosol and defines the levels of background, to estimate the impact. It is assumed that the snow sampling particulate matter in the atmosphere during the fall, providing information on the chemical characteristics of the air column crossed. Quantify the changes in the chemistry of snow can be useful to complete the balance of the contributions of particulate matter to the soil and their effects on the ecosystem, knowing that they have potential negative environmental [9-11]. In addition, the trace elements may allow to recognize traces of various sources of aerosols both natural and anthropogenic [
Precipitation, liquid and solid, are important mechanisms of atmospheric deposition, especially in remote areas. Several studies, from the last 20 - 30 years [
The monitoring stations of particulate are difficult to be managed in mountainous areas, which are characterized by long periods with thermal states below zero. Nevertheless, these areas are particularly interesting for the analysis of transboundary aerosol, both for the low human impact that for their localization at high altitudes. Therefore, the present study evaluated the potential of chemical and morphological characteristics of the particles, to determine local and transboundary contributions through samples of stratigraphic sections of snow that have taken place during the entire winter 2010. Some researchers have shown that it is not negligible the impact that the contaminants accumulated during the winter season can have on natural resources during and after the melting of snow in spring [17,18]. In areas of permanent snow and glaciers, contaminants may be subject to deep burial resulting in inclusion in the layers of ice [19,20]. Hence the possibility of having information on the evolution over time of the particulates, through the study of carrots performed in glaciers [19,21,22].
The estimation of the particulate in the snow also has repercussions on the evaluations of the overall energy balance, since the impurities and the sizes of the particles control the absorption of solar radiation, while the temperature controls the emission of radiation at low wavelengths [
Some models have shown that the high absorption of small particles in concentrations of about 1 ppm may decrease the albedo of the visible snow, mainly due to the reduction of the coefficient of scattering. In some studies it has been shown that the albedo decreases exponentially from 20% to 60% in perennial snow with a particulate concentration from 102 to 103 - 104 μg/m3 [24,25].
In literature, studies carried out on the snow and ice of Greenland and Antarctica have shown the presence of toxic trace elements (lead and cadmium). On the basis of stratigraphic position and historical assessments based on light isotopes, it was possible to interpret the causes of these enrichments, attributing the anomalies in atmospheric emissions from anthropogenic sources in the period of the Greek-Roman two millennia before the Industrial Revolution, probably due to ancient mining and smelting activities [26,27]. These anomalies are characterized by relations between elements for emission sources of the industrial revolution. Air pollution from 1700 to the present has been documented for several heavy metals, including Pb, Cd, Cu and Zn [28-30], Hg [
The interest on the study of trace elements present in the snows and glaciers at mid-latitudes is of great interest, because of rapid economic growth and industrialization developed in recent decades, resulting in high levels of anthropogenic pollution in the atmosphere [58,59]. These studies have been done both in relatively remote areas, such as the Andes Mountains [
In this study we analyzed samples of snow, to distinguish the contributions of anthropogenic origin from those of natural origin, taking samples in the Dolomites in winter 2010. All samples were analyzed in ion chromatography and ICP-MS in order to know the chemical composition and in SEM-EDS for morphological characterization.
The samples were made in the central Dolomites and in the Adamello-Presanella Massif (Trentino Alto AdigeNorth of Italy), near Alpe Pampeago (Tesero-Val di Fiemme-Trento), in the snow fields of Monsorno (altitude 2010 m), Tresca (altitude 2080 m) and Presena Glacier (altitude 2730 m). The Monsorno field presents an exposure S while the Tresca field with an exposure NNW, they are far from each other less than one kilometre (
Val di Fiemme is one of the main valleys of the Dolomites and is located in eastern Trentino. Together with Val di Fassa and Val di Cembra, is the catchment area of Avisio, left tributary of the river Adige. This area is very large (~400 Km2) and it is approximately 180 Km from Adriatic Sea. It is surrounded to the N with Dolomites of Gardena and Fassa (Bolzano), to E with Dolomites of Feltre and the Pale di San Martino (Community Primiero), to SE with Pre Alpes Bellunesi (Community Valsugana), to S with Pre Alpes Vicentine, to W with Dolomites of Brenta and Alps of Val di Non (Community Cembra Valley), to NW with Alps Sarentine. The Dolomites di Fiemme are called mountains and not Dolomiti for their composition non-dolomitic, they shall consist, in fact, by silicate (granites and metamorphic rocks as porphyry) with a minor presence of carbonate and dolomite, and are located entirely in Trentino Alto Adige. The highest peak is Cima d’Asta with its 2847 m above sea level. During the winter season, Dolomitic area is often affected by strong continental thermal anticyclones that determine a mostly stable and very cold weather and lead to a strong minimum rainfall between December and February. The snowy weather conditions derived from passages of warm fronts from the Atlantic or the cyclogenesis on the Genoa Gulf, that attract masses of very hot and humid air from the Mediterranean (mainly orographic snowfall).
During the different phases of sampling, the main meteorological characteristics were collected at an altitude from 1760 m to 2730 m: air temperature and temperature of the superficial layer of the snow. Through the penetrometric battage profile, it was possible analysed a layer of snow of 4 m depth (Ghiacciaio Presena—2730 m), identifying each individual substrate. Then, through a process of dec-climatological analysis it was possible to
know the sources that produce volcanic ash, or desert sands, or other contributions of transboundary aerosol. During the stratigraphic analysis, some samples were collected through coring and they were subsequently analyzed by SEM, ICP-MS and ion chromatography in the Department of the University of Ferrara, allow to obtain qualitative and quantitative analysis of the snow, and defining the chemical composition to know the source of emission.
The sampling was done in Pampeago Alp and in Presena Glacier at different times of the year 2010, during monitoring season of avalanches. February 18, March 11, April 11, May 12, therefore different meteorological conditions cannot be avoid. The meteorological data (temperature, humidity, wind direction and wind velocity) were respectively provided by METEOTRENTINO weather station of Cavalese-Alpe Cermis and Capanna Presena (2750 m). The first weather station is situated at 2200 m and was the nearest station to Pampeago Alps. The distance from station to sampling sites ranged from 4 to 5 km from SSW. Near the snow field of Capanna Presena automatic weather station complete with snow gauge ultrasonic is placed.
The sampling during the first campaign (February 18, 2010) was carried out from 10 am to 13 pm (UTC + 1). The synoptic situation is characterized by a depression centred on Ireland, with a secondary low pressure field located on the ground near the Corsica Island and at high altitude (500 hPa geopotential) on the south of Sardinia. This facilitated the arrival of humid and warm current from southern Mediterranean basin (Libeccio at middle altitude and Scirocco at ground) to the Dolomites, with moderate snowfall above 1200 m. The average wind speed were 3 Km/h and direction to the south (the trajectories were created using the software online NOAA HYSPLIT MODEL-GDAS Meteorological Data—
The sampling during the third campaign (April 11, 2010) was carried out at the Presena Glacier (2750 m from 12 am to 2:30 pm (UTC + 1). The synoptic situation is characterized by inflow of cold air from the northeastern and arising from thermal contrast between the Russian anticyclone and a depression extending from eastern France and Styria. These currents cause a sudden drop in temperature, with variable weather and isolated snow showers over 1000 m. At 2500 m, the average wind speed and direction were 9 Km/h and from the north (Figures 2(c) and 3(c)). Low values of relative humidity (37%) and temperature (Tmin −8˚C and Tmax −3˚C at 2730 m) maintained the environment stable and wet during the sampling. Also for this sampling, three samples were collected: 40 cm depth, 100 cm depth and 140 cm depth.
The sampling during the fourth campaign (May 12, 2010) was carried out from 11 am to 2:30 pm (UTC + 1) at Presena Glacier. The synoptic situation shows a range of pressures levelled to a low centre of south-western Europe with a strong anticyclone located on North Africa (
The instruments used for sampling were simple plastic tins, previously cleaned with MilliQ® water, with doublesealed cap. After collection, all samples were transported in a refrigerated cooler to UNIFE laboratory in Ferrara and stored under refrigeration until microscopy analysis was performed [
The samples were used for SEM-EDS analysis to characterize the shape and morphology and the elemental composition of aerosol particles collected. Morphological characteristics, size and elemental analysis of individual particles were performed with a Scanning Electron Microscopy (SEM) (Zeiss EVO 40) equipped with an Energy Dispersive X-ray Spectrometer (EDS) (INCA 300 OXFORD) for X-ray microanalysis. The particle size and the surface morphology of sampled aerosol particles were investigated in high resolution mode (up to 20.000×) with a working voltage of 20 kV which correspond to the detection limit of 1 µm particle size. The analyses were qualitative and were performed in the manually mode. SEM-EDS is often employed to identify airborne particulate deposits and biological materials [
The multi-element analysis was carried out by Inductively Coupled Plasma Mass Spectrometry (ICP-MS, X Series spectrometer, collision/reaction cell CCTED, Thermo Electron Corporation), which has become an increasingly popular technique for characterization of atmospheric aerosols [
• 1 cc of the snow solution was diluted with 8 cc H2O MilliQ® and 1 cc of standard Rh Re (100 ppb);
• 50 cc of the snow solution were filtered by syringe with a polypropylene VWR filter 0.45 μm. Then, 1 cc of the snow filtered solution was diluted with 8 cc H2O MilliQ® and 1 cc of standard Rh Re (100 ppb).
For the IC analysis we used the ion chromatograph Dionex ICS2000, which uses of an eluent of carbonatebicarbonate. The anions are separated by an ion-exchange resin, low-capacity and highly basic and direct in a strong acid cation exchanger (suppressor), where they are converted into an acid form with high conductivity and the eluent is transformed into carbonic acid with weak conductivity. Therefore, the anions are measured for conductometry and compared with the standards on the basis of the retention times. The quantization is done by measuring the peak area or height. For IC analysis, 100 cc of each snow solution samples were injected in the instrument and analyzed.
For each sample, SEM measurements were conducted on particles which were not in contact with any others. High-resolution images of particles were obtained by regulation of vacuum inside the instrument chamber. Several distinct particle shapes were observed, which were single particles rounded (
Aerosol composition of single particle was determined using EDS microanalysis which detected the presence of C, O, Na, Mg, Al, Si, P, S, Cl, K, Ca, Mn and Fe. The chemical composition of the analyzed particles can be divided in five main categories: allumo silicate (