G Sangiorgi

Sources of high PM2.5 concentrations in Milan, Northern Italy: Molecular marker data and CMB modelling

In Milan (MI), the largest city in Northern Italy, the annually average PM2.5 concentration is above 25 μg m(-3), the value that the EU established as a target for 2010, and the upper limit from 2015 onwards (2008/30/CE). Over a three-year period (2006-2009) PM concentrations and chemical compositions were measured in an urban site (MI), a rural site (OB) and a remote site (ASC) in Northern Italy. Chemical characterization (EC/OC, inorganic ions, elements, C20-C32 n-alkanes, C2-C5 mono and dicarboxylic acids, levoglucosan and PAHs) was carried out on PM2.5 samples from the three sites, and PM10 from MI. Molecular markers were used in Chemical Mass Balance (CMB) modelling to estimate the contributions of primary sources to OC, and then PM mass from each source was reconstructed in MI, OB and ASC for different seasons. Estimates of the traffic (TR) source contribution to PM2.5 mass ranged from 4.1 (± 2.0) μg m(-3) during the summer, to 13.3 (± 6.7) μg m(-3) during the winter in MI. TR was the main primary source for PM2.5 concentrations in MI (17-24%). Its contribution was lower at the OB site (7-9%) and at the remote ASC site (3-4%). TR is a local source, while biomass burning (BB) is a diffuse regional source in Northern Italy: during fall and winter, BB was 25-30% and 27-31% of PM2.5 at MI and OB respectively. Other primary sources accounted for a small amount of the PM2.5, i.e. natural gas combustion (0-1%), plant debris (0-4%), road dust (RD=0-4%; but 15% at ASC during winter and 10% of PM10 at MI during summer) and sea salt (0-1%). Secondary inorganic+organic aerosol constituted the major part of the PM2.5 mass during spring and summer (50-65%) at the three sites.

Particle size, chemical composition, seasons of the year and urban, rural or remote site origins as determinants of biological effects of particulate matter on pulmonary cells

Particulate matter (PM), a complex mix of chemical compounds, results to be associated with various health effects. However there is still lack of information on the impact of its different components. PM2.5 and PM1 samples, collected during the different seasons at an urban, rural and remote site, were chemically characterized and the biological effects induced on A549 cells were assessed. A Partial Least Square Discriminant Analysis has been performed to relate PM chemical composition to the toxic effects observed. Results show that PM-induced biological effects changed with the seasons and sites, and such variations may be explained by chemical constituents of PM, derived both from primary and secondary sources. The first-time here reported biological responses induced by PM from a remote site at high altitude were associated with the high concentrations of metals and secondary species typical of the free tropospheric aerosol, influenced by long range transports and aging.

Vertical profiles of aerosol absorption coefficient from micro-Aethalometer data and Mie calculation over Milan

Vertical profiles of aerosol number-size distribution and black carbon (BC) concentration were measured between ground-level and 500m AGL over Milan. A tethered balloon was fitted with an instrumentation package consisting of the newly-developed micro-Aethalometer (microAeth® Model AE51, Magee Scientific, USA), an optical particle counter, and a portable meteorological station. At the same time, PM(2.5) samples were collected both at ground-level and at a high altitude sampling site, enabling particle chemical composition to be determined. Vertical profiles and PM(2.5) data were collected both within and above the mixing layer. Absorption coefficient (b(abs)) profiles were calculated from the Aethalometer data: in order to do so, an optical enhancement factor (C), accounting for multiple light-scattering within the filter of the new microAeth® Model AE51, was determined for the first time. The value of this parameter C (2.05±0.03 at λ=880nm) was calculated by comparing the Aethalometer attenuation coefficient and aerosol optical properties determined from OPC data along vertical profiles. Mie calculations were applied to the OPC number-size distribution data, and the aerosol refractive index was calculated using the effective medium approximation applied to aerosol chemical composition. The results compare well with AERONET data. The BC and b(abs) profiles showed a sharp decrease at the mixing height (MH), and fairly constant values of b(abs) and BC were found above the MH, representing 17±2% of those values measured within the mixing layer. The BC fraction of aerosol volume was found to be lower above the MH: 48±8% of the corresponding ground-level values. A statistical mean profile was calculated, both for BC and b(abs), to better describe their behaviour; the model enabled us to compute their average behaviour as a function of height, thus laying the foundations for valid parametrizations of vertical profile data which can be useful in both remote sensing and climatic studies.

Distribution of n-alkanes in the Northern Italy aerosols: data handling of GC-MS signals for homologous series characterization.

The paper describes the characterization of n-alkane homologous series present in PM samples performed by gas chromatography-mass spectrometry analysis. The PM samples were collected in three locations in northern Italy: Milan, a large urban area, Oasi Bine, a rural site far from big city centers, and Alpe San Colombano, a remote, high altitude site in the Alps. They represent different particle sizes (PM(1), PM(2.5), PM(10)) and seasons (summer, fall, and winter). The analyzed samples were characterized in terms of PM total mass, total concentration of C(20)-C(32) n-alkanes and carbon preference index, CPI, to quantify the relative abundance of odd versus even n-alkanes. As alternative to the conventional method based on peak integration, a chemometric approach based on autocovariance function (EACVF) computation was found reliable to characterize the homologous series. In particular two parameters have proven useful chemical markers for tracking the biogenic and anthropogenic origins of n-alkanes: CPI(EACVF) and series %, estimating the % n-alkanes abundance relative to total alkane concentration. The investigated samples display a large variation in the n-alkanes relative abundance: the lowest values (series % = 1-14%) were found in summer and the highest (series % = 24-48%) in winter. In addition, a considerable seasonal variation of CPI(EACVF) values can be identified for all the sampling sites: the CPI(EACVF) values are close to 1 (CPI(EACVF) = 0.8-1.2) in the cold seasons, revealing a strong contribution from anthropogenic emissions, while spreader values (CPI(EACVF) = 0.9-3) were found in the warm season, that is, reflecting a variable contribution from biogenic sources in combination with anthropogenic emissions.

Vertical distribution of hydrocarbons in the low troposphere below and above the mixing height: Tethered balloon measurements in Milan, Italy

A novel approach for measuring vertical profiles of HCs and particle number concentrations was described and applied in the low troposphere over Milan (Italy) during typical spring and summer days. Particle profiles yielded nearly homogeneous concentrations below the mixing height, with level-to-ground concentration ratios of 92-97%, while HCs showed a more pronounced decrease (74-95%). Vertical mixing and photochemical loss of HCs were demonstrated to cause these gradients. Much lower concentrations were observed for the profiles above the mixing height, where the HC mixtures showed also a different composition, which was partially explained by the horizontal advection of air with HC sources different to those prevailing at the site. The application of pseudo-first order kinetics for reactions between HCs and the hydroxyl radical allowed for the estimation of the vertical mixing time scale in the order of 100 ± 20 min.

Vertical Profiles and Chemical Properties of Aerosol Particles upon Ny-Ålesund (Svalbard Islands)

Size-segregated particle samples were collected in the Arctic (Ny-Alesund, Svalbard) in April 2011 both at ground level and in the free atmosphere exploiting a tethered balloon equipped also with an optical particle counter (OPC) and meteorological sensors. Individual particle properties were investigated by scanning electron microscopy coupled with energy dispersive microanalysis (SEM-EDS). Results of the SEM-EDS were integrated with particle size and optical measurements of the aerosols properties at ground level and along the vertical profiles. Detailed analysis of two case studies reveals significant differences in composition despite the similar structure (layering) and the comparable texture (grain size distribution) of particles in the air column. Differences in the mineral chemistry of samples point at both local (plutonic/metamorphic complexes in Svalbard) and remote (basic/ultrabasic magmatic complexes in Greenland and/or Iceland) geological source regions for dust. Differences in the particle size and shape are put into relationship with the mechanism of particle formation, that is, primary (well sorted, small) or secondary (idiomorphic, fine to coarse grained) origin for chloride and sulfate crystals and transport/settling for soil (silicate, carbonate and metal oxide) particles. The influence of size, shape, and mixing state of particles on ice nucleation and radiative properties is also discussed.

Data handling of GC/MS signals for characterization of PAH sources in Northern Italy aerosols.

The paper describes the characterization of polycyclic aromatic hydrocarbons (PAHs) in atmospheric aerosol samples using Gas Chromatography-Mass Spectrometry analysis. A data handling of GC/MS signals based on Experimental Autocovariance Function (EACVF) is described in order to directly characterize PAHs with a simple and reliable method suitable for processing large batches of samples. The method was successfully applied to 42 aerosol samples collected in different seasons (summer, fall and winter) in two locations in Northern Italy: Milan, a large urban area, and Oasi Le Bine, a rural site. The reliability of the EACVF results was verified by comparison with the values computed with the conventional GC/MS signal treatment and the data of independent studies. Two main emission sources were identified and described by PAH concentration profiles: the road traffic source (TR), characterized by high contributions of FLNT, PYR and CHR, and the residential combustion (COMB) mainly containing pyrogenic high molecular weight PAHs, i.e., CHR, BaP, BeP, BbF and BkF. In addition, some PAH diagnostic ratios were directly computed for the EACVF plot, to distinguish between traffic and combustion dominated emissions, i.e. the ratios CHR/BaP, PYR/BaP and PYR/BeP.

Semivolatile PAH and n -alkane gas/particle partitioning using the dual model: up-to-date coefficients and comparison with experimental data

The gas/particle partitioning coefficient Kp, of a semivolatile compound is a key parameter for its atmospheric fate. The most complete method of predicting Kp for polycyclic aromatic hydrocarbons (PAHs) is offered by the dual model, as it describes both the adsorption on soot and absorption into organic matter processes. However, experimental and model data exist almost exclusively for PAHs. In order to bridge this gap, experimental data on the phase partitioning of both PAHs and n-alkanes were collected at an urban and a remote site. Moreover, all the necessary parameters (e.g., octanol–air and soot–air partitioning coefficients) for the dual model have been collected and updated or (if missing) estimated for the first time. The results point out that both absorption and adsorption seem to contribute to the partitioning of PAHs and n-alkanes. However, it seems that the dual model always underestimates the particle sorption not only for PAHs but also for n-alkanes.

Aerosol dynamics upon Terni basin (Central Italy): results of integrated vertical profile measurements and electron microscopy analyses

In this work, aerosol size distribution measurements along with individual particle analyses were performed along the vertical profile in the atmosphere, to shed some light on the dynamics of evolution of aerosol properties upon a basin valley. The case study is the Terni basin, one of the most polluted urban and industrial sites in central Italy. Aerosol vertical profile measurements were performed using a helium-filled tethered balloon equipped with an optical particle counter (OPC), a miniaturized cascade impactor with particle collection filter, and a portable meteorological station. Combined OPC number size measurements and single particle analyses by scanning electron microscopy were employed to reconstruct the pattern and evolution of aerosol properties over the basin. Moreover, the CHIMERE chemistry-transport model was applied over a selected computing domain to obtain a general overview of the driving forces of the aerosol dynamics. Scanning electron microscopy methods along with chemical transport modeling revealed distinct distributions of number, size and geochemical properties of different particles classes in the aerosols. These reflect distinct behaviours and spatial/temporal evolution of the constituent particles, along with the common occurrence of dust inputs from regional to long range sources (e.g., Saharan dust inputs). All these features have to be taken into consideration when approaching the modeling of atmospheric processes, particularly in basin valleys located in Central and Southern Italy where the influence of Saharan dust outbreaks is more pronounced.

Nitration of pollen aeroallergens by nitrate ion in conditions simulating the liquid water phase of atmospheric particles

Pollen aeroallergens are present in atmospheric particulate matter (PM) where they can be found in coarse biological particles such as pollen grains (aerodynamic diameter dae>10μm), as well as fragments in the finest respirable particles (PM2.5; dae<2.5μm). Nitration of tyrosine residues in pollen allergenic proteins can occur in polluted air, and inhalation and deposition of these nitrated proteins in the human respiratory tract may lead to adverse health effects by enhancing the allergic response in population. Previous studies investigated protein nitration by atmospheric gaseous pollutants such as nitrogen dioxide and ozone. In this work we report, for the first time, a study on protein nitration by nitrate ion in aqueous solution, at nitrate concentrations and pH conditions simulating those occurring in the atmospheric aerosol liquid water phase. Experiments have been carried out on the Bovine serum albumin (BSA) protein and the recombinant Phleum pratense allergen (Phl p 2) both in the dark and under UV-A irradiation (range 4-90Wm-2) to take into account thermal and/or photochemical nitration processes. For the latter protein, modifications in the allergic response after treatment with nitrate solutions have been evaluated by immunoblot analyses using sera from grass-allergic patients. Experimental results in bulk solutions showed that protein nitration in the dark occurs only in dilute nitrate solutions and under very acidic conditions (pH<3 for BSA; pH<2.2 for Phl p 2), while nitration is always observed (at pH0.5-5) under UV-A irradiation, both in dilute and concentrated nitrate solutions, being significantly enhanced at the lowest pH values. In some cases, protein nitration resulted in an increase of the allergic response.