Hybrid multiple-site mass closure and source apportionment of PM2.5 and aerosol acidity at major cities in the Po Valley.

This study investigates the major chemical components, particle-bound water content, acidity (pH), and major potential sources of PM2.5 in major cities (Belluno, Conegliano, Vicenza, Mestre, Padua, and Rovigo) in the eastern end of the Po Valley. The measured PM2.5 mass was reconstructed using a multiple-site hybrid chemical mass closure approach that also accounts for aerosol inorganic water content (AWC) estimated by the ISORROPIA-II model. Annually, organic matter accounted for 31-45% of the PM2.5 at all sites, followed by nitrate (10-19%), crustal material (10-14%), sulfate (8-10%), ammonium (5-9%), elemental carbon (4-7%), other inorganic ions (3-4%), and trace elements (0.2-0.3%). Water represented 7-10% of measured PM2.5. The ambient aerosol pH varied from 1.5 to 4.5 with lower values in summer (average in all sites 2.2 ± 0.3) and higher in winter (3.9 ± 0.3). Six major PM2.5 sources were quantitatively identified with multiple-site positive matrix factorization: secondary sulfate (34% of PM2.5), secondary nitrate (30%), biomass burning (17%), traffic (11%), re-suspended dust (5%), and fossil fuel combustion (3%). Biomass burning accounted for ~90% of total PAHs. Inorganic aerosol acidity was driven primarily by secondary sulfate, fossil fuel combustion (decreasing pH), secondary nitrate, and biomass burning (increasing pH). Secondary nitrate was the primary driver of the inorganic AWC variability. A concentration-weighted trajectory (multiple-site) analysis was used to identify potential source areas for the various factors and modeled aerosol acidity. Eastern and Central Europe were the main source areas of secondary species. Less acidic aerosol was associated with air masses originating from Northern Europe owing to the elevated presence of the nitrate factor. More acidic particles were observed for air masses traversing the Po Valley and the Mediterranean, possibly due to the higher contributions of fossil fuel combustion factor and the loss of nitric acid due to its interaction with coarse sea-salt particles.

A procedure to evaluate the factors determining the elemental composition of PM2.5. Case study: the Veneto region (northeastern Italy).

The Po Valley is one of the most important hot spots in Europe for air pollution. Morphological features and anthropogenic pressures lead to frequent breaching of air quality standards and to high-pollution episodes in an ~46 × 103-km2-wide alluvial lowland. Therefore, it is increasingly important to study the air quality in a wide geographical scale to better implement possible and successful mitigation measures. The Veneto region lies in the eastern part of the Po Valley and the elemental composition of PM has been mainly studied in the Venice area, whereas scarce data are available for the remaining territory of the region. In this study, the elemental composition of PM2.5 was investigated over 1 year (2012-2013) at six major cities of the Veneto region. Samples were analyzed for 16 elements (Ca, Al, Fe, S, K, Mg, Ti, Mn, Zn, Ba, As, Ni, Pb, Sb, V, and Cu), and results were processed to investigate spatial and seasonal variations, the influence of meteorological factors, and the most probable sources by using a procedure based on (i) elemental ratios (Cu/Sb, Cu/Zn, Cu/Pb, Mn/V, V/Ni, and Zn/Pb), (ii) cluster analysis on wind data, and (iii) conditional probability function (CPF). The percentage of elements in PM2.5 ranged between 11 and 20%, and Ca and S were the most abundant elements in the region. Typical seasonal variations and similar trends were exhibited by each element, especially in the lowland. Some elements such as Zn, K, Mn, Pb, and Sb were found at high concentrations during the cold period. However, no similar dispersion processes were observed throughout the region, and their concentrations were mostly depending on individual local sources. In the alpine and foothill parts of the region, lower concentrations were recorded with respect to the Po Valley cities, which resulted enriched of most of the elements considered in this study. The cluster analysis on wind data and the CPF of the ratio-related sources demonstrated that a widespread pollution condition exists in the region, apart from the coastal area. However, specific directions (e.g., a link with high-traffic roads, industrial areas, and airports) resulted the most probable explanation for each ratio-related source. In addition, the Veneto region hosts one of the most important Mediterranean ports for the cruise sector (Venice harbor), and its impact was previously demonstrated in the historical city center. In this study, the impact of Venice shipping emissions was estimated to be 3.5% of PM2.5 in some particular days.

Estimation of local and external contributions of biomass burning to PM2.5 in an industrial zone included in a large urban settlement.

A total of 85 PM2.5 samples were collected at a site located in a large industrial zone (Porto Marghera, Venice, Italy) during a 1-year-long sampling campaign. Samples were analyzed to determine water-soluble inorganic ions, elemental and organic carbon, and levoglucosan, and results were processed to investigate the seasonal patterns, the relationship between the analyzed species, and the most probable sources by using a set of tools, including (i) conditional probability function (CPF), (ii) conditional bivariate probability function (CBPF), (iii) concentration weighted trajectory (CWT), and (iv) potential source contribution function (PSCF) analyses. Furthermore, the importance of biomass combustions to PM2.5 was also estimated. Average PM2.5 concentrations ranged between 54 and 16 µg m-3 in the cold and warm period, respectively. The mean value of total ions was 11 µg m-3 (range 1-46 µg m-3): The most abundant ion was nitrate with a share of 44 % followed by sulfate (29 %), ammonium (14 %), potassium (4 %), and chloride (4 %). Levoglucosan accounted for 1.2 % of the PM2.5 mass, and its concentration ranged from few ng m-3 in warm periods to 2.66 µg m-3 during winter. Average concentrations of levoglucosan during the cold period were higher than those found in other European urban sites. This result may indicate a great influence of biomass combustions on particulate matter pollution. Elemental and organic carbon (EC, OC) showed similar behavior, with the highest contributions during cold periods and lower during summer. The ratios between biomass burning indicators (K+, Cl-, NO3-, SO42-, levoglucosan, EC, and OC) were used as proxy for the biomass burning estimation, and the contribution to the OC and PM2.5 was also calculated by using the levoglucosan (LG)/OC and LG/PM2.5 ratios and was estimated to be 29 and 18 %, respectively.