The oxidative potential (OP) of PM2.5 was investigated during two measurement campaigns in 2024 (winter and summer) done simultaneously at an urban background and a traffic site. The research provides unprecedented chemical detail for this region, integrating elemental analysis (ED-XRF), carbonaceous fractions (OC/EC, WSOC), major ions, organic tracers (sugars/levoglucosan), and water-soluble organic nitrogen (WSON). The OP was quantified by using two assays: dithiothreitol (OPDTT) and ascorbic acid (OPAA). Source apportionment revealed competing trends of sources limiting spatial and seasonal variabilities and distinct drivers for the two OP assays. Traffic emerged as the primary contributor to OPAA at both sites, while OPDTT was influenced by traffic, secondary organic aerosols (SOAs), biomass burning, and resuspension/construction. Sea spray, nitrate, and construction-related emissions significantly impacted OPDTT but had a negligible effect on OPAA. Primary biological aerosols (fungal spores) influenced the OPAA. Seasonal variations showed dominance of traffic and biomass burning in winter (50-60% of OP), whereas sulfate and SOA became prominent during summer, for OPDTT. OPAA peaked in summer, while OPDTT peaked in winter. Traffic-induced SOA exhibits a higher redox activity relative to its mass contribution, opposite to sulfate. Season-dependent mitigation strategies could be useful to effectively reduce the oxidative burden of PM2.5.

Urban air pollution from road traffic remains a major public health concern, with its spatial variability at neighbourhood scales strongly influenced by urban morphology. This study investigates how urban form affects the dispersion of traffic-related PM2.5 in four Italian cities (Lecce, Bari, Milan and Rome) representing diverse climatic and morphological contexts. Seasonal simulations were conducted using the ADMS-Roads dispersion model, integrating detailed road geometries, standardized traffic emissions, and city-level meteorological data for 2019-2021. Urban morphology was characterized at 100 m resolution using building plan area fraction (lambda(p)), street-canyon aspect ratio and mean building height derived from GIS analyses. Statistical analysis combined random forest regression with partial dependence plots and quantile regression to explore both average and distributional effects. Results reveal a generally negative association between lambda(p) and PM2.5 in Lecce, Milan, and Rome, particularly at higher concentration quantiles, suggesting that denser urban fabrics may mitigate extreme pollution episodes. Bari exhibits a weaker and more heterogeneous response, highlighting the influence of local wind regimes and traffic distribution. Wind speed and temperature consistently reduce PM2.5 across all cities, while street geometry effects are non-linear and season-dependent. These findings demonstrate the importance of considering urban morphology alongside traffic and meteorology when designing strategies to reduce exposure. Importantly, the methodological framework presented here, combining high-resolution dispersion modelling with interpretable machine-learning analyses, is transferable to other urban contexts, providing a robust approach to assess morphology-pollution interactions beyond the studied cities.

The water-soluble fraction of particulate matter (PM) is the most bio-accessible and potentially harmful component due to its ability to be absorbed through the respiratory tract. This study evaluates the content of water-soluble organic carbon (WSOC) and water-soluble total nitrogen (WSTN) in PM2.5 and PM10 filters collected in the Lecce area (Italy), focusing on monthly samples from different site typologies and daily samples from a single background site. WSOC was quantified using two methods on aqueous extracts with a TOC-L CPH analyser: (1) the total organic carbon (TOC) method, which determines WSOC as the difference between total carbon (TC) and inorganic carbon (IC); and (2) the non-purgeable organic carbon (NPOC) method, which removes inorganic carbon by acidification and air purging before TC measurement. The analytical parameters of the NPOC method were optimized using a Design of Experiment (DoE), while WSTN, equivalent to total soluble nitrogen in the extract, was measured simultaneously using the NPOC method in N-mode. Results showed a strong correlation and high consistency between the two WSOC methods, with overall combined averages of WSOCTOC = (3.3 +/- 0.5) mu g/m3 and WSOCNPOC = (3.2 +/- 0.4) mu g/m3. OC solubility was high and similar in both PM fractions, averaging 65 % in PM2.5 and 66 % in PM10 but demonstrated a clear seasonal variability, with higher WSOC/OC ratios in the cold season. Furthermore, the NPOC approach facilitates the simultaneous quantification of WSTN with a reduced sample volume, and the data confirmed the limited content of watersoluble organic nitrogen (WSON) in this dataset, thus enhancing analytical efficiency for routine monitoring.

In May and June 2025, wildfires in Canada produced atmospheric effects extending beyond North America. Large quantities of gases and aerosols emitted by biomass combustion were transported across the Atlantic and reached Europe. Here, our aim is to investigate how these events affect the variability of climate-altering species in Italy using observations from permanent observatories.Clear evidences of this long-range transport were observed from 8th June 2025 at the GAW/WMO Global Station “O. Vittori” at Monte Cimone (2165 m a.s.l., northern Italy) and at the Potenza CIAO observatory (760 m a.s.l., southern Italy), two co-located sites for the Research Infrastructures ICOS and ACTRIS. It was also observed, albeit with weaker intensity, at the ACTRIS Environmental-Climate Observatory (ECO) in Lecce (37 m a.s.l., southern Italy). Atmospheric transport modelling (LAGRANTO and HYSPLIT back-trajectories) confirmed that the air masses affecting the sites originated in North America.Average daily carbon monoxide (CO) values peaked to 207 ppb on 9th June at CMN and to 247 ppb at ECO, nearly doubling the levels measured during the preceding 7 days. Also, black carbon (BC) showed marked increases, with values more than doubling the average of the preceding days at both sites.Additional confirmation of the plume’s arrival and vertical evolution was provided by the ALICE-Net ceilometer at CMN: between 6th and 8th June, aerosol-rich layers were detected at high altitudes before gradually descending to the measurement site. At CIAO, the aerosol lidar observed smoke layers between 11 and 14 km from 5th to 10th June.CO and ozone (O₃) remained high until 13th June at CMN (average values: 188 ppb and 70 ppb), and at ECO (average CO value of 232 ppb, O3 data not available). Subsequently, intermediate values have been observed from 14th to 21st June. At CIAO, CO increased between 8th and 17th June, reaching up to 250 ppb.No corresponding increases in carbon dioxide (CO₂) have been observed during the wildfire plume event. During the days characterized by the peaks in CO and O3 (8th – 13th June), daily mean CO2 values showed a – 6.4 ppm and – 3.4 ppm decrease with respect to the previous 7 days at CMN and ECO. The analysis of back-trajectories showed air masses travelling at pressure levels representative of the European PBL, where active ecosystems could take up CO₂, in the 24 hours before the arrival at CMN.The analysis of the day-to-day variability of nighttime/daytime N2O, CO2 and δ13CO2, pointed to a significant influence of air masses from the regional PBL to CMN during the daytime on 9th – 14th and 18th – 19th June. This suggests that emissions occurring at regional scale could contribute to the observed atmospheric composition variability. Together with the role of air mass mixing and in-plume chemical processes along transport, this implies that attributing the observed enhancements to wildfire emissions requires careful and critical evaluation.Acknowledgments: Observations/analyses are supported by the ITINERIS (PE0000021, NRRP – NextGenerationEU) and PRO-ICOS MED (PON 2014–2020) projects, funded by the Italian Ministry of University and Research and the European Union.

Biomass burning processes affect many semi-rural areas in the Mediterranean, but there is a lack of long-term datasets focusing on their classification, obtained by monitoring carbonaceous particle concentrations and optical properties variations. To address this issue, a campaign to measure equivalent black carbon (eBC) and particle number size distributions (0.3–10 μm) was carried out from August 2019 to November 2020 at a coastal semi-rural site in the Basilicata region of Southern Italy. Long-term datasets were useful for aerosol characterization, helping to clearly identify traffic as a constant eBC source. For a shorter period, PM2.5 mass concentrations were also measured, allowing the estimation of elemental and organic carbon (EC and OC), and chemical and SEM (scanning electron microscope) analysis of aerosols collected on filters. This multi-instrumental approach enabled the discrimination among different biomass burning (BB) processes, and the analysis of three case studies related to domestic heating, regional smoke plume transport, and a local smoldering process. The AAE (Ångström absorption exponent) daily pattern was characterized as having a peak late in the morning and mean hourly values that were always higher than 1.3.

The study of the atmospheric particulate matter (PM) oxidative potential (OP), a general indicator of human health risks associated with PM exposure, has become a focal point in research. In Italy, the number of studies concerning OP is limited, especially for the fine fraction of PM. This study aims to compare the impact of different natural and anthropogenic sources on fine PM (PM2.5) and its OP on three areas of Southern Italy. A study of PM2.5 sources sampled at a rural site was carried out. The PM2.5 sources were identified and characterized with the Positive Matrix Factorization (PMF5.0) model, while the contribution of each source to the OP estimated with the multi-linear regression (MLR) analysis. Results were compared with those obtained from two similar studies, related to different typology sites in south Italy. The PMF5.0 identified similar sources for the three sites, with different contributions to PM2.5 and OP. The MLR analysis highlights that combustion sources are the main contributors to the OP activity of PM2.5. The relative contributions to OP and PM2.5 are not comparable for all sources. Results of this study represent a contribution to a better understanding of the po- tential health impact caused by PM2.5; of its spatial variability; and role of different sources.

Several research efforts were devoted to investigate long-term trends of carbonaceous aerosols in atmospheric particulate matter. Carbon is known to affect climate, human health, and cultural heritage being an important component also for planning future policies. This work investigates the longest dataset of carbon content (EC and OC) in PM2.5 and PM10 fractions available in south Italy (2015-2022). Equivalent black carbon (eBC) was determined hourly in PM10, using the multi-angle absorption photometer (MAAP), and it was used to evaluate the trend of the mass absorption coefficient (MAC) determined in-situ. PM2.5 and its OC and EC content showed a statistically significant decreasing trend throughout years, since 2017-2018, approximately-5 % yr(-1), falling in the ranges reported for other urban background sites in Europe. The decrease of PM10 and its carbon content was more limited, approximately-2 % yr-1 but it was not statistically significant (p > 0.05). Temporal analysis revealed that seasonality played the most significant role in concentration pattern of PM and carbonaceous species, including secondary organic aerosol (SOC) and EC/OC ratio, compared to weekly or daily variabilities, with the highest daily values in winter/autumn. This was likely due to the contributions of biomass burning (for domestic heating and agricultural practices) and of road traffic both larger at this site during the autumn/winter. The value of MAC in-situ was 12.4 f 1.2 m2g(-1) (as geometric mean f standard deviation) or 12.6 f 2.5 m2g(-1) (as arithmetic mean f standard deviation), showing a slight increase during summer and early autumn compared to the other season. MAC showed an increasing long-term trend of 2.5 % yr(-1).

Carbonaceous aerosols represent a significant component of atmospheric aerosol, with implications for climate and human health. The recent EU Directive 2024/2881 highlights the need to monitor emerging pollutants like black carbon more effectively. This study presents an brief field campaign at an urban background site aimed at characterizing carbonaceous aerosols. Daily samples of PM10 and PM2.5 were analyzed using a Sunset thermal-optical analyzer to determine organic and elemental carbon (OC, EC), while real-time equivalent black carbon (eBC) was measured with three independent instruments: MAAP, AE33, and Giano BC1. Total carbon (TC) was monitored using an online TCA08 thermo-catalytic analyzer. The average concentration of PM10 was 17.1 µg/m3 and 10.4 µg/m3 for PM2.5. On average, OC and EC represented 16.5% and 3.6% of PM10 mass, and 22.6% and 5.5% of PM2.5. SOC accounted for 36% of OC. The in situ Mass Absorption Cross-section (MAC), recalculated for the ECO site, was between 8.0 and 12.2 m2/g. eBC concentrations were modulated by the daily evolution of the planetary boundary-layer height and combustion sources. The apportionment of eBC was 65% from fossil fuel and 35% from biomass burning. Biomass-burning emissions were further confirmed by optical measurements, with BrC contributing 35% of absorption at 370 nm.

Oxidative potential (OP) is a potential indicator of negative health effects of particulate matter (PM). To address mitigation strategies, there is need of understanding how natural and anthropogenic sources influence OP at different sites. This work investigates spatial and seasonal variabilities of PM2.5 and PM10 concentrations, composition, and oxidative potential (OPDTTV, obtained with DTT assay), simultaneously at 22 sites in a central Mediterranean area in south Italy. Source apportionment using PMF5 allowed to evaluate the contributions of eight sources: traffic, biomass burning (BB), nitrate, sulphate-rich, marine, crustal, carbonates/construction, and industrial (only for PM2.5). Nitrate, traffic, and BB had larger contributions during the cold season and presented spatial variability with exclusion of nitrate. Industrial contributions did not have relevant seasonal or spatial variability. The other sources had an opposite trend with larger values during the warm season but only sulphate-rich had non-negligible spatial variability. OPDTTV had relevant spatial variability only during the cold season. Four sources had statistically significant contributions to OPDTTV: traffic, BB, sulphate-rich, and crustal (in descending order). The use of soluble and insoluble fractions of OC and Ca in PMF5 allowed a better separation between traffic and BB sources and allowed to determine the role of local construction works. The results may have implications in future policies for mitigation strategies of OP targeting specific sources categories.

Abstract. Energy-dispersive X-ray fluorescence (ED-XRF) is a versatile non-destructive technique to evaluate elemental composition of atmospheric particulate matter (PM) without the need for sample preparation and with high potentiality in source apportionment studies. It is usually applied on Teflon or polycarbonate substrates; however, it would be preferable to use quartz substrates for the possibility to use the same substrate also for carbon detection. In this work an intercomparison among five laboratories on PM10 samples collected on Teflon and quartz filters was done with the specific purpose of understanding the performance of the ED-XRF technique applied to samples collected on quartz substrates. Limits of detection (LODs) on quartz substrates were significantly larger than those on Teflon for the majority of the elements with the exclusion of Cl, Mn, Cu, and Rb, which had comparable LODs for the two substrates. Repeatability on PM10 samples collected on quartz and Teflon substrates was comparable and, on average, better than 10 % for the majority of the elements analysed and better than 5 % for several elements. Comparisons of analysis on Teflon filters for 20 elements obtained by the different laboratories were in the range of ±15 % of the 1:1 line for most of the elements and laboratories. Comparison of measurements on samples collected on quartz and Teflon substrates showed that 17 elements were well correlated (R > 0.7) with average Cquartz/CTeflon ratios in the range 0.6 ± 0.1 (for light elements, due to self-absorption effects) to 1.1 ± 0.1 for the majority of the cases. This suggested that reasonable results could be obtained on quartz substrates for 17 elements, including Na, Mg, and Al, using calibration on Teflon and the ratios Cquartz/CTeflon as correction factors. However, these correction factors were dependent on the instrument and method used for the analysis.

Atmospheric new particle formation (NPF) is a naturally occurring phenomenon, during which high concentrations of sub-10 nm particles are created through gas to particle conversion. The NPF is observed in multiple environments around the world. Although it has observable influence onto annual total and ultrafine particle number concentrations (PNC and UFP, respectively), only limited epidemiological studies have investigated whether these particles are associated with adverse health effects. One plausible reason for this limitation may be related to the absence of NPF identifiers available in UFP and PNC data sets. Until recently, the regional NPF events were usually identified manually from particle number size distribution contour plots. Identification of NPF across multi-annual and multiple station data sets remained a tedious task. In this work, we introduce a regional NPF identifier, created using an automated, machine learning based algorithm. The regional NPF event tag was created for 65 measurement sites globally, covering the period from 1996 to 2023. The discussed data set can be used in future studies related to regional NPF.

Considering the scarce number of studies investigating the oxidative potential of PM2.5 in Italy, a measurement campaign was conducted from February 2020 to October 2020 in a coastal semi-rural site of Basilicata (Southern Italy) with the goal to characterize the fine fraction of ambient particulate matter (PM) and investigate its chemical and toxicological properties, by means of oxidative potential. Different instruments such as an automatic low-volume sampler, an aethalometer and an optical particle counter, were employed for the measurement of PM2.5 mass concentration, equivalent black carbon (eBC) concentration and absorption Ångström exponent (AAE), and particle number size distribution in 0.25–31 μm size range, respectively. 108 daily PM samples, collected on quartz fibre filters, were chemically analysed. Organic (OC) and elemental (EC) carbon content was estimated by thermo-optical transmittance technique (TOT), the concentrations of the main water-soluble ions and total elements were determined by ion chromatography and ED-XRF technique, while the oxidative potential of the water-soluble fraction was estimated through the dithiothreitol (DTT) assay. The mean value of PM2.5 mass concentration was 9.2 ± 2.5 μg/m3 and the average contribution of measured species on PM2.5 mass was 3.3% EC; 19.3% OC; 27.0% secondary inorganic aerosol (sum of SO42−, NH4+ and NO3−), and 10.2% of the other ions and elements. The OC and EC contributions to PM2.5 mass and their mean ratio (OC/EC = 6.6 ± 3.1) suggest that the site is affected by the combined contribution of traffic emissions and biomass combustion (domestic heating and agricultural activities), with the latter prevailing over the traffic, as supported by the mean AAE value of 1.3. The mean OP normalised by sampled volume, OPDTTV, was as high as 0.34 ± 0.22 nmol/min·m3, a value comparable to those recorded for PM2.5 in suburban areas of Italy. The correlation between OPDTTV and the chemical species observed in the PM2.5 samples showed a good agreement with the carbonaceous component OC (r = 0.62) and with some ions, K+ and SO42− (r = 0.60). These results identify combustion sources as the most responsible for the relatively high OPDTTV activity of PM2.5 recorded in this area.

Urban air pollution, exacerbated by vehicular emissions, poses a significant health threat, especially in densely populated areas. This study, part of the PNRR Italian National Center for Sustainable Mobility (MOST), aims to assess the impact of vehicular pollutants in urban environments. Focusing on Lecce and Bari (Italy), the research integrates data from dispersion models and meteorological analyses to evaluate pollutant concentrations. Preliminary analysis of eight urban areas in Lecce and six in Bari reveals trends in PM10 concentrations influenced by urban morphology and wind dynamics. These findings underscore the essential role of sustainable mobility strategies in mitigating urban air pollution and promoting healthier urban environments.

Ultrafine particles (UFP, those with diameters ≤ 100 nm), have been reported to potentially penetrate deeply into the respiratory system, translocate through the alveoli, and affect various organs, potentially correlating with increased mortality. The aim of this study is to assess long-term trends (5-11 years) in mostly urban UFP concentrations based on measurements of particle number size distributions (PNSD). Additionally, concentrations of other pollutants and meteorological variables were evaluated to support the interpretations. PNSD datasets from 12 urban background (UB), 5 traffic (TR), 3 suburban background (SUB) and 1 regional background (RB) sites in 15 European cities and 1 in the USA were evaluated. The non-parametric Theil-Sen's method was used to detect monotonic trends. Meta-analyses were carried out to assess the overall trends and those for different environments. The results showed significant decreases in NO, NO2, BC, CO, and particle concentrations in the Aitken (25-100 nm) and the Accumulation (100-800 nm) modes, suggesting a positive impact of the implementation of EURO 5/V and 6/VI vehicle standards on European air quality. The growing use of Diesel Particle Filters (DPFs) might also have clearly reduced exhaust emissions of BC, PM, and the Aitken and Accumulation mode particles. However, as reported by prior studies, there remains an issue of poor control of Nucleation mode particles (smaller than 25 nm), which are not fully reduced with current DPFs, without emission controls for semi-volatile organic compounds, and might have different origins than road traffic. Thus, contrasting trends for Nucleation mode particles were obtained across the cities studied. This mode also affected the UFP and total PNC trends because of the high proportion of Nucleation mode particles in both concentration ranges. It was also found that the urban temperature increasing trends might have also influenced those of PNC, Nucleation and Aitken modes.

There is a body of evidence that ultrafine particles (UFP, those with diameters <= 100 nm) might have significant impacts on health. Accordingly, identifying sources of UFP is essential to develop abatement policies. This study focuses on urban Europe, and aims at identifying sources and quantifying their contributions to particle number size distribution (PNSD) using receptor modelling (Positive Matrix Factorization, PMF), and evaluating long-term trends of these source contributions using the non-parametric Theil-Sen's method. Datasets evaluated include 14 urban background (UB), 5 traffic (TR), 4 suburban background (SUB), and 1 regional background (RB) sites, covering 18 European and 1 USA cities, over the period, when available, from 2009 to 2019. Ten factors were identified (4 road traffic factors, photonucleation, urban background, domestic heating, 2 regional factors and long-distance transport), with road traffic being the primary contributor at all UB and TR sites (56-95 %), and photonucleation being also significant in many cities. The trends analyses showed a notable decrease in traffic-related UFP ambient concentrations, with statistically significant decreasing trends for the total traffic-related factors of -5.40 and -2.15 % yr(-1) for the TR and UB sites, respectively. This abatement is most probably due to the implementation of European emissions standards, particularly after the introduction of diesel particle filters (DPFs) in 2011. However, DPFs do not retain nucleated particles generated during the dilution of diesel exhaust semi-volatile organic compounds (SVOCs). Trends in photonucleation were more diverse, influenced by a reduction in the condensation sink potential facilitating new particle formation (NPF) or by a decrease in the emissions of UFP precursors. The decrease of primary PM emissions and precursors of UFP also contributed to the reduction of urban and regional background sources.

Atmospheric particulate matter (PM) is one of the major risks for global health. The exact mechanisms of toxicity are still not completely understood leading to contrasting results when different toxicity metrics are compared. In this work, PM10 was collected at three sites for the determination of acellular oxidative potential (OP), intracellular oxidative stress (OSGC), cytotoxicity (MTT assay), and genotoxicity (Comet assay). The in vitro tests were done on the A549 cell line. The objective was to investigate the correlations among acellular and intracellular toxicity indicators, the variability among the sites, and how these correlations were influenced by the main sources by using PMF receptor model coupled with MLR. The OPDTTV, OSGCV, and cytotoxicity were strongly influenced by combustion sources. Advection of African dust led to lower-than-average intrinsic toxicity indicators. OPDTTV and OSGCV showed site-dependent correlations suggesting that acellular OP may not be fully representative of the intracellular oxidative stress at all sites and conditions. Cytotoxicity correlated with both OPDTTV and OSGCV at two sites out of three and the strength of the correlation was larger with OSGCV. Genotoxicity was correlated with cytotoxicity at all sites and correlated with both, OPDTTV and OSGCV, at two sites out of three. Results suggest that several toxicity indicators are useful to gain a global picture of the potential health effects of PM.

In this work, new particle formation events (NPFs) occurring at two locations in southern Italy, the urban background site of Lecce (ECO station) and the coastal site of Lamezia Terme (LMT station), are identified and analyzed. The study aims to compare the properties of NPF events at the two sites, located 225 km away from each other and characterized by marked differences in terms of emission sources and local weather dynamics. Continuous measurements of particle number size distributions, in the size range from 10 to 800 m, were performed at both sites by a mobility particle size spectrometer (MPSS). The occurrence of NPF events, observed throughout the study period that lasted 5 years, produced different results in terms of frequency of occurrence: 25 % of the days at ECO and 9 % at LMT. NPF events showed seasonal patterns: higher frequency during spring and summer at the urban background site and the autumn–winter period at the coastal site. Some of these events happened simultaneously at both sites, indicating the occurrence of the nucleation process on a large spatial scale. Cluster analysis of 72 h back trajectories showed that during the NPF events the two stations were influenced by similar air masses, most of which originated from the north-western direction. Local meteorological conditions characterized by high pressure, with a prevalence of clear skies, low levels of relative humidity (RH < 52 %), and moderate winds (3–4 m s−1) dominated the NPF events at both sites. Notable differences were observed in SO2 and PM2.5 concentrations and H2SO4 proxy levels, resulting in ∼65 %, ∼80 %, and 50 % lower levels at LMT compared to ECO, respectively. It is likely that the lower level of that which is recognized as one of the main gas precursors involved in the nucleation process could be responsible for the smaller NPF frequency of occurrence (∼60 % less than ECO) observed in LMT.

Many countries imposed lockdown (LD) to limit the spread of COVID-19, which led to a reduction in the emission of anthropogenic atmospheric pollutants. Several studies have investigated the effects of LD on air quality, mostly in urban settings and criteria pollutants. However, less information is available on background sites, and virtually no information is available on particle number size distribution (PNSD). This study investigated the effect of LD on air quality at an urban background site representing a near coast area in the central Mediterranean. The analysis focused on equivalent black carbon (eBC), particle mass concentrations in different size fractions: PM2.5 (aerodynamic diameter Da < 2.5 mu m), PM10 (Da < 10 mu m), PM10-2.5 (2.5 < Da < 10 mu m); and PNSD in a wide range of diameters (0.01-10 mu m). Measurements in 2020 during the national LD in Italy and period immediately after LD (POST-LD period) were compared with those in the corresponding periods from 2015 to 2019. The results showed that LD reduced the frequency and intensity of high-pollution events. Reductions were more relevant during POST-LD than during LD period for all variables, except quasi-ultrafine particles and PM10-2.5. Two events of long-range transport of dust were observed, which need to be identified and removed to determine the effect of LD. The decreases in the quasi-ultrafine particles and eBC concentrations were 20%, and 15-22%, respectively. PM2.5 concentration was reduced by 13-44% whereas PM10-2.5 concentration was unaffected. The concentration of accumulation mode particles followed the behaviour of PM2.5, with

Airborne transmission of SARS-CoV-2 has been object of debate in the scientific community since the beginning of COVID-19 pandemic. This mechanism of transmission could arise from virus-laden aerosol released by infected individuals and it is influenced by several factors. Among these, the concentration and size distribution of virus-laden particles play an important role. The knowledge regarding aerosol transmission increases as new evidence is collected in different studies, even if it is not yet available a standard protocol regarding air sampling and analysis, which can create difficulties in the interpretation and application of results. This work reports a systematic review of current knowledge gained by 73 published papers on experimental determination of SARS-CoV-2 RNA in air comparing different environments: outdoors, indoor hospitals and healthcare settings, and public community indoors. Selected papers furnished 77 datasets: outdoor studies (9/77, 11.7%) and indoor studies (68/77. 88.3%). The indoor datasets in hospitals were the vast majority (58/68, 85.3%), and the remaining (10/68, 14.7%) were classified as community indoors. The fraction of studies having positive samples, as well as positivity rates (i.e. ratios between positive and total samples) are significantly larger in hospitals compared to the other typologies of sites. Contamination of surfaces was more frequent (in indoor datasets) compared to contamination of air samples; however, the average positivity rate was lower compared to that of air. Concentrations of SARS-CoV-2 RNA in air were highly variables and, on average, lower in outdoors compared to indoors. Among indoors, concentrations in community indoors appear to be lower than those in hospitals and healthcare settings.

We present an overview of the concentrations and distributions of water-soluble ion species and elemental components in ambient particulate matter for five measurement sites in southern Italy with the aim of investigating the influence of the different site characteristics on PM levels. The sites encompass different characteristics, ranging from urban to coastal and high-altitude remote areas. PM10 and PM2.5 fractions were collected simultaneously using dual channel samplers during the winter period from November 2015 to January 2016 and analyzed for water-soluble ion species, using ion chromatography, and elemental composition, using inductively coupled plasma mass spectrometry (ICP-MS). In all sites, PM2.5 represented the higher contribution to particulate mass, usually more than two times that of the coarse fraction (PM2.5−10). At the coastal site in Capo Granitola (Western Sicily), sea salts constituted about 30% of total PM10 mass. On average, ion species accounted for 30% to 60% of total PM10 mass and 15% to 50% of PM2.5 mass. We found that secondary ion species, i.e., SO42−, NO3− and NH4+ dominated the identifiable components within both PM2.5 and PM10 fractions. The chlorine–sodium ratio was usually lower than that expected from the natural level in sea salt, evidencing aged air masses. At the monitoring site in Naples, a highly urbanized area affected by high levels of anthropogenic source emissions, an increased contribution of ammonium was found, which was imputed to the increased ammonia emissions from industrial combustion sources and road traffic. The concentrations of the investigated elements showed noteworthy differences from one site to another. The PM10 fraction was highly enriched by sources of anthropogenic origin in the samples from the most urbanized areas. In general, the enrichment factors of the elements were similar between the PM10 and PM2.5 fractions, confirming common sources for all elements.