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

Chemical Composition of PM10 in 16 Urban, Industrial and Background Sites in Italy

Italy is characterized by a very variable configuration in terms of altitude, proximity to the sea, latitude and the presence of industrial plants. This paper summarizes the chemical characterization of PM10 obtained from 38 sampling campaigns carried out in 16 sites in Italy during the years 2008–2018. Chemical determinations include all macro-components (six macro-elements, eight ions, elemental carbon and organic carbon). The sum of the individual components agrees well with the PM10 mass. The chemical composition of the atmospheric aerosol clearly reflects the variety in the Italian territory and the pronounced seasonal variations in the meteoclimatic conditions that characterize the country. Macro-sources reconstruction allowed us to identify and evaluate the strength of the main PM10 sources in different areas. On 10 sampling sites, the soluble and insoluble fractions of 23 minor and trace elements were also determined. Principal Component Analysis was applied to these data to highlight the relationship between the elemental composition of PM10 and the characteristics of the sampling sites.

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 PM_2.5 in major cities (Belluno, Conegliano, Vicenza, Mestre, Padua, and Rovigo) in the eastern end of the Po Valley. The measured PM_2.5 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 PM_2.5 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 PM_2.5. 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 PM_2.5 sources were quantitatively identified with multiple-site positive matrix factorization: secondary sulfate (34% of PM_2.5), 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.

Acid-extractable heavy metals in PM2.5 over Xi'an, China: seasonal distribution and meteorological influence

To investigate the acid-extractable heavy metals in fine particulate matter (PM_2.5) over Xi'an, China, 24-h PM_2.5 samples were collected every 3 days from December 2015 through November 2016. The bioavailable fraction, termed here the bioavailability index (BI), of PM_2.5-bound metal (As, Ba, Cd, Co, Cu, Mn, Ni, Pb, Ti, V, and Zn) and potential influencing factors, including relative humidity, temperature, air pressure, wind speed, visibility, PM_2.5, and SO₂ concentrations, were assessed in this study. The annual average PM_2.5 concentration was 50.6 ± 35.6 μg m^-3, 1.5 times higher than the Chinese national secondary standard. Zn, Ti, and As were the most abundant elements of those analyzed in the PM_2.5 samples, accounting for 72.1% of total quantity. The seasonal variations and enrichment factor analysis of heavy metals revealed that coal combustion in winter was a crucial source of Pb, Co, Cu, and Zn; and dust resuspension in spring contributed considerable Mn, Ti, and V. The acid-extractable fractions of the measured metals varied. Pb, Cu, Mn, and Zn exhibited relatively high acid-extractable concentrations and BI values. Pb was mostly in the acid-extractable fraction in PM_2.5, with a mean BI value of 66.7%, the highest in summer (69.8%) and lowest in winter (63.7%). Moreover, the BIs of PM_2.5-bound heavy metals were inversely related to temperature and wind speed, whereas positively correlated with relative humidity, SO₂, and PM_2.5 concentration in this study. This study assessed the seasonal distribution and meteorological influence of acid-extractable heavy metals, providing a deeper understanding of atmospheric heavy metal pollution in Xi'an, China.