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

Pollution characteristics, source apportionment, and health risk assessment of PM10 and PM2.5 in rooftop and kerbside environment of Lanzhou, NW China

To investigate air pollution in the kerbside environment and its associated human health risks, a study was conducted in Lanzhou during December 2018, as well as in April, June, and September 2019. The research aimed to characterize the composition of PM10 and PM2.5, including elements, ions, and carbonaceous components, at both rooftop and kerbside locations. Additionally, source apportionment and health risk assessment were conducted. The results showed that the average mass concentrations of PM10 on the rooftop were 176.01 ± 83.23 μg/m3, and for PM2.5, it was 94.07 ± 64.89 μg/m3. The PM10 and PM2.5 levels at the kerbside are 2.21 times and 1.79 times, respectively, greater than those on the rooftop. Moreover, the concentrations of elements, ions, and carbonaceous components in kerbside PM were higher than those at the rooftop location. Chemical mass closure analysis identified various sources, including organic matter, mineral dust, secondary ions, other ions, elements, and other components. In comparison to rooftop particulate matter (PM), mineral dust makes a more substantial contribution to kerbside PM. Secondary ions show an opposite trend, making a greater contribution to rooftop PM. The contribution of organic components within PM of the same particle size remains relatively consistent. The outcome of the health risk assessment indicates that Co, Cd, and As in PM within the kerbside and rooftop environments do not pose a notable carcinogenic risk. However, Al and Mn do present specific non-carcinogenic risks, particularly in the kerbside environment. Furthermore, children experience elevated non-carcinogenic risk compared to adults. These findings can serve as a scientific foundation for formulating policies within the local health department.

Aerosol characterization and peculiarities of source apportionment in Moscow, the largest and northernmost European megacity

High population and a wide range of activities in a megacity lead to large-scale ecological consequences which require the assessment with respect to distinct characteristics of climate, location, fuel consumption, and emission sources. In-depth study of aerosol characteristics was carried out in Moscow, the largest megacity in Europe, during the cold period (autumn and winter) and in spring. PM10 chemical speciation based on carbonaceous matter, water-soluble ions, and elements was carried out to reconstruct the PM mass and evaluate the primary and secondary aerosol contribution. For the whole study period organic matter, mineral dust, and secondary inorganic/organic accounted for 34, 24, and 16 % of PM10 mass, respectively. PM10, OC, and EC approached a maximum in spring and decreased in winter. Mineral dust seasonal fraction increased from spring (17 %) to autumn (32 %), and then decreased in winter (22 %). Secondary inorganic aerosols (SIA) in opposite showed the maximum 27 % in winter. K+ marked the residential biomass burning in the region surrounding a megacity in spring and autumn, agriculture fires in spring. In winter primary aerosol contribution dropped down 56 % while secondary approached practically equal 44 %. Source factors with the relative contributions are quantified, namely city dust (26 %), traffic (23 %), industrial (20 %), biomass burning (12 %), secondary (12 %), and de-icing salt (7 %); they were significantly varying between the cold heating period and springtime. The relevance of sources to meteorological parameters and mass transportation is investigated by using both bivariate polar plots and Lagrangian integrated trajectory (HYSPLIT) model. Trajectory clustering demonstrates regional sources being crucial contributors to PM10 pollution. Aerosol speciation and source apportion factors identify the differences of the Moscow urban background among large European and Asian cities due to northern climate conditions, fast construction, long-range transport from industrial-developing area surrounding a city, regional biomass burning preferably in spring and autumn, and winter road management.

Source apportionment of suspended particulate matter (PM1, PM2.5 and PM10) collected in road and tram tunnels in Krakow, Poland

Here, we present the results of a comprehensive study of air quality in two tunnels located in the city of Krakow, southern Poland. The study comprised three PM fractions of suspended particulate matter (PM1, PM2.5 and PM10) sampled during campaigns lasting from March 14 to April 24, 2016 and from June 28 to July 18, 2016, in the road tunnel and the tram tunnel, respectively. The collected samples had undergone comprehensive chemical, elemental and carbon isotope analyses. The results of these analyses gave the basis for better characterization of urban transport as a source of air pollution in the city. The concentrations of particulate matter varied, depending on the analysed PM fraction and the place of sampling. For the tram tunnel, the average concentrations were 53.2 µg·m-3 (PM1), 73.8 µg·m-3 (PM2.5), 96.5 µg·m-3 (PM10), to be compared with 44.2 µg·m-3, 137.7 µg·m-3, 221.5 µg·m-3, respectively, recorded in the road tunnel. The isotope-mass balance calculations carried out separately for the road and tram tunnel and for each PM fraction, revealed that 60 to 79% of carbon present in the samples collected in the road tunnel was associated with road transport, to be compared with 15-33% obtained in the tram tunnel. The second in importance were biogenic emissions (17-21% and 41-49% in the road and tram tunnel, respectively. Sixteen different polycyclic aromatic hydrocarbons (PAHs) have been identified in the analysed samples. As expected, much higher concentrations of PAHs were detected in the road tunnel when compared to the tram tunnel. Based on the analysed PAHs concentrations, health risk assessment was determined using 3 different types of indicators: carcinogenic equivalent (CEQ), mutagenic equivalent (MEQ) and toxic equivalent (TEQ).

A PM10 chemically characterized nation-wide dataset for Italy. Geographical influence on urban air pollution and source apportionment

Urban textures of the Italian cities are peculiarly shaped by the local geography generating similarities among cities placed in different regions but comparable topographical districts. This suggested the following scientific question: can different topographies generate significant differences on the PM10 chemical composition at Italian urban sites that share similar geography despite being in different regions? To investigate whether such communalities can be found and are applicable at Country-scale, we propose here a novel methodological approach. A dataset comprising season-averages of PM10 mass concentration and chemical composition data was built, covering the decade 2005-2016 and referring to urban sites only (21 cities). Statistical analyses, estimation of missing data, identification of latent clusters and source apportionment modeling by Positive Matrix Factorization (PMF) were performed on this unique dataset. The first original result is the demonstration that a dataset with atypical time resolution can be successfully exploited as an input matrix for PMF obtaining Country-scale representative chemical profiles, whose physical consistency has been assessed by different tests of modeling performance. Secondly, this dataset can be considered a reference repository of season averages of chemical species over the Italian territory and the chemical profiles obtained by PMF for urban Italian agglomerations could contribute to emission repositories. These findings indicate that our approach is powerful, and it could be further employed with datasets typically available in the air pollution monitoring networks.

Anthropogenic pollutants induce enhancement of aerosol acidity at a mountainous background atmosphere in southern China

Aerosol acidity plays a crucial role in atmospheric physicochemical processes, climate change and human health, particularly in the formation of secondary organic aerosols (SOA). However, understanding the characteristics and driving factors of aerosol acidity in background mountains has been limited. In this study, we conducted intensive field measurements in the Nanling mountains during the dry and wet seasons to analyze aerosol pH characteristics and their driving factors using sensitivity tests. The mean aerosol pH in the background mountains was found to be 2.68 ± 0.55, with values ranging from 0.38 to 4.44, significantly lower than predicted values in northern China. Sensitivity tests revealed that aerosol acidity in the background atmosphere was more responsive to dominant chemical species (T-NH3 (= NH4+ + NH3) and SO42-) rather than relative humidity and temperature. Additionally, we observed that sulfate and ammonium, transported occasionally by dryer northern air masses, had a substantial impact on decreasing aerosol pH at the site. Similar to the southeastern United States, NH4+/NH3 also dominated the total buffer capacity of aerosol acidity in the Nanling mountains. The strong aerosol acidity in this area is expected to have adverse effects on regional air quality and climate by enhancing SOA formation and regulating the dry deposition of inorganic reactive nitrogen.

The variability of mass concentrations and source apportionment analysis of equivalent black carbon across urban Europe

This study analyzed the variability of equivalent black carbon (eBC) mass concentrations and their sources in urban Europe to provide insights into the use of eBC as an advanced air quality (AQ) parameter for AQ standards. This study compiled eBC mass concentration datasets covering the period between 2006 and 2022 from 50 measurement stations, including 23 urban background (UB), 18 traffic (TR), 7 suburban (SUB), and 2 regional background (RB) sites. The results highlighted the need for the harmonization of eBC measurements to allow for direct comparisons between eBC mass concentrations measured across urban Europe. The eBC mass concentrations exhibited a decreasing trend as follows: TR > UB > SUB > RB. Furthermore, a clear decreasing trend in eBC concentrations was observed in the UB sites moving from Southern to Northern Europe. The eBC mass concentrations exhibited significant spatiotemporal heterogeneity, including marked differences in eBC mass concentration and variable contributions of pollution sources to bulk eBC between different cities. Seasonal patterns in eBC concentrations were also evident, with higher winter concentrations observed in a large proportion of cities, especially at UB and SUB sites. The contribution of eBC from fossil fuel combustion, mostly traffic (eBCT) was higher than that of residential and commercial sources (eBCRC) in all European sites studied. Nevertheless, eBCRC still had a substantial contribution to total eBC mass concentrations at a majority of the sites. eBC trend analysis revealed decreasing trends for eBCT over the last decade, while eBCRC remained relatively constant or even increased slightly in some cities.

Mass, composition, and sources of particulate matter in residential and traffic sites of an urban environment

Present study aims to assess the mass, composition, and sources of PM₁₀ and PM_2.5 (particulate matter having aerodynamic diameter less than or equal to 10 and 2.5 µm aerodynamic diameter, respectively) in Vellore city. Seasonal samples collected in traffic and residential sites were analyzed for ions, elements, organic carbon (OC), and elemental carbon (EC). Source apportionment of PM₁₀ and PM_2.5 is carried out using Chemical Mass Balance, Unmix, Positive Matrix Factorization and Principal Component Analysis receptor models. Results showed that traffic site had higher annual concentration (PM_2.5 = 62 ± 32 and PM₁₀ = 112 ± 23 µg m^-3) when compared to residential site (PM_2.5 = 54 ± 22 and PM₁₀ = 98 ± 20 µg m^-3). Al, Ca, Fe, K, and Mg known to have crustal origin dominated the element composition irrespective of PM size and sampling site. Among ions, SO₄^2- accounted highest in both sites with an average of 70 and 60% to PM_2.5 and PM₁₀ ionic mass. Elemental carbon contribution to PM mass was found highest in traffic site (PM_2.5 = 17 to 23% and PM₁₀ = 8 to 10%) than residential site (PM_2.5 = 9 to 17% and PM₁₀ = 4 to 8%). Elements, ions, OC, and EC accounted 12, 28, 34, and 16% of PM_2.5 mass and 12, 21, 20, and 8% of PM₁₀ mass, respectively. Different sources identified by the receptor models are resuspended road dust, crustal material, secondary aerosol, traffic, non-exhaust vehicular emissions, secondary nitrate, construction, cooking, and biomass burning. Since Vellore is aspiring to be a smart city, this study can help the policymakers in effectively curbing PM.

Apportioning PM1 in a contrasting receptor site in the Mediterranean region: Aerosol sources with an updated sulfur speciation

A multi-parametric experimental campaign was performed in Agri Valley (Basilicata, southern Italy) from July 2017 to January 2018. The investigated area, though basically rural and devoted to agricultural activities, hosts a huge on-shore oil reservoir, i.e. Centro Olio Val d'Agri (COVA), bringing substantial environmental modifications and impacts to the district landscape. Daily concentrations of PM₁ aerosol samples, Equivalent Black Carbon and number size distributions were evaluated. Chemical aerosol speciation based on elemental and ion analyses were carried out and source apportionment by Positive Matrix Factorization (PMF) was applied to reconstruct PM₁ source profile. The most significant emission sources found are torches from the oil treatment facility (37 % w/w), an unresolved factor constituted by soil resuspension, Saharan dust, and biomass burning (24 % w/w), ammonium sulphate (23 % w/w), emissions from the oil desulfurization (Claus process) (13 % w/w), and traffic + road dust (3 % w/w). SEM analysis on PM₁ single particles allowed to confirm the finding from PMF including the occurrence of elemental sulfur associated with the Claus process. The novelty of the present study consists in the identification of this latter fingerprint.

Oxidation of Catechols at the Air-Water Interface by Nitrate Radicals

Abundant substituted catechols are emitted to, and created in, the atmosphere during wildfires and anthropogenic combustion and agro-industrial processes. While ozone (O₃) and hydroxyl radicals (HO^•) efficiently react in a 1 μs contact time with catechols at the air-water interface, the nighttime reactivity dominated by nitrate radicals (NO₃) remains unexplored. Herein, online electrospray ionization mass spectrometry (OESI-MS) is used to explore the reaction of NO₃(g) with a series of representative catechols (catechol, pyrogallol, 3-methylcatechol, 4-methylcatechol, and 3-methoxycatechol) on the surface of aqueous microdroplets. The work detects the ultrafast generation of nitrocatechol (aromatic) compounds, which are major constituents of atmospheric brown carbon. Two mechanisms are proposed to produce nitrocatechols, one (equivalent to H atom abstraction) following fast electron transfer from the catechols (QH₂) to NO₃, forming NO₃^- and QH₂^•+ that quickly deprotonates into a semiquinone radical (QH^•). The second mechanism proceeds via cyclohexadienyl radical intermediates from NO₃ attack to the ring. Experiments in the pH range from 4 to 8 showed that the production of nitrocatechols was favored under the most acidic conditions. Mechanistically, the results explain the interfacial production of chromophoric nitrocatechols that modify the absorption properties of tropospheric particles, making them more susceptible to photooxidation, and alter the Earth's radiative forcing.

Dust emission reduction enhanced gas-to-particle conversion of ammonia in the North China Plain

Ammonium salt is an important component of particulate matter with aerodynamic diameter less than 2.5 µm (PM_2.5) and has significant impacts on air quality, climate, and natural ecosystems. However, a fundamental understanding of the conversion kinetics from ammonia to ammonium in unique environments of high aerosol loading is lacking. Here, we report the uptake coefficient of ammonia (γ_NH3) on ambient PM_2.5 varying from 2.2 × 10^-4 to 6.0 × 10^-4 in the North China Plain. It is significantly lower than those on the model particles under simple conditions reported in the literature. The probability-weighted γ_NH3 increases obviously, which is well explained by the annual decrease in aerosol pH due to the significant decline in alkali and alkali earth metal contents from the emission source of dust. Our results elaborate on the complex interactions between primary emissions and the secondary formation of aerosols and the important role of dust in atmospheric chemistry.

Insights to the 3D internal morphology and metal oxidation states of single atmospheric aerosol particles by synchrotron-based methodology

The morphology and metal oxidation states of atmospheric aerosols are pertinent to their formation processes and ensuing interactions with surrounding gases, vapors and other environments upon deposition, such as human respiratory tract, soil and water. Although much progress has been made in recent years through single-particle techniques, considerably less is known with respect to the three-dimensional (3D) internal morphology of single atmospheric aerosol particles due to the limited penetration depth of electron microscopy. In this study, for the first time, a novel synchrotron-based transmission X-ray microscopy (TXM) methodology has been developed to visualize the 3D internal chemical mixing state and structure of single particles. The results show that the TXM is more applicable to the imaging of solid particles containing high-density elements, e.g., iron (Fe), aluminum (Al), silicone (Si), carbon (C) and sulfur (S), and/or solid particles of sizes larger than about 100 nm. In addition, the TXM is capable to reveal the fine 3D topographic features of single particles. The derived 3D internal and external information would be difficult to discern in the 2D images from electron microscopy. The TXM 3D images illustrate that aerosol particles exhibit complex internal mixing state and structure, e.g., homogeneously-, heterogeneously-mixed, multiple inclusions, fibrous, porous, and core-shell configuration. When coupled with the synchrotron-based X-ray fluorescence spectrometry (XRF) and absorption near-edge spectroscopy (XANES) of an X-ray nanoprobe in the energy range of 4-15 keV, the 3D morphology of single particles is further supplemented with the spatial distribution and oxidation sates of selected elements, including Fe, vanadium (V), manganese (Mn), chromium (Cr) and arsenic (As). The presented cross-platform, synchrotron-based methodology shows promise in complementing existing single-particle techniques and providing new insights to the heterogeneity of single-particle micro-physicochemical states relevant to the aerosol chemistry, optical properties, and their environmental and health impacts.

The Physiological Effects of Air Pollution: Particulate Matter, Physiology and Disease

Nine out of 10 people breathe air that does not meet World Health Organization pollution limits. Air pollutants include gasses and particulate matter and collectively are responsible for ~8 million annual deaths. Particulate matter is the most dangerous form of air pollution, causing inflammatory and oxidative tissue damage. A deeper understanding of the physiological effects of particulate matter is needed for effective disease prevention and treatment. This review will summarize the impact of particulate matter on physiological systems, and where possible will refer to apposite epidemiological and toxicological studies. By discussing a broad cross-section of available data, we hope this review appeals to a wide readership and provides some insight on the impacts of particulate matter on human health.

Characteristics of aerosol chemistry and acidity in Shanghai after PM2.5 satisfied national guideline: Insight into future emission control

With continuous endeavors to control air pollutant emissions, the average concentration of PM_2.5 in Shanghai in 2019-2020 satisfied the national secondary standard (35 μg m^-3) for the first time. In this study, the two-year dataset of hourly resolution PM_2.5 compositions observed in downtown Shanghai was used to investigate the relative contribution of sulfate and nitrate as well as particulate acidity. The average concentration of SO₂ was reduced to 7.7 μg m^-3, while the concentration of NO_x remained above 40 μg m^-3, indicating that the control of SO₂ was more effective than that of NO_x during the 13th Five-Year Plan period. Thus, the sulfate pollution was significantly reduced whereas the nitrate loading remained almost constant. The monthly N/S ratio varied from below 0.6 to above 2.0, indicating that the contribution of automobile exhaust to PM_2.5 is seasonally dependent. Contrary to sulfate, the nitrate fraction increased rapidly with the increase of PM_2.5 mass, suggesting that the explosive growth of nitrate has become a major driver of haze formation. ISORROPIA simulations show that PM_2.5 was moderately acidic with pH values following the trend of winter > spring > autumn > summer. The diurnal variation of nitrate was related to the changes in aerosol water content, indicating the effect of heterogeneous aqueous reactions on secondary aerosol formation. The effectiveness of emission control for reducing inorganic PM_2.5 varied with different gas precursors and seasons. The abatement of NH₃ emissions will increase particle acidity and acid rain pollution, although it is more effective than that of NO_x when the emission reduction is larger than 60%. This study suggests that the control of vehicle exhaust should be given priority in the Yangtze River Delta for coordinately mitigating PM_2.5 and acid rain pollution.

Characterization of Aerosol Pollution in Two Hungarian Cities in Winter 2009–2010

In this study, atmospheric particulate matter (APM) pollution was compared in urban background sites of two cities in Hungary—namely the capital Budapest and Debrecen—by analyzing daily aerosol samples collected between 8 December 2009 and 18 March 2010. Concentration, elemental composition, including BC, and sources of fine (PM2.5) and coarse (PM2.5–10) aerosol pollution, as well as their variation due to meteorological conditions and anthropogenic activities, were determined for both cities. The average PM2.5 concentrations were 22 μg/m3 and 17 μg/m3 in Budapest and Debrecen, respectively. In the case of PM10, the mean concentration was 32 μg/m3 in Budapest and 23 μg/m3 in Debrecen. The concentration of the coarse fraction decreased significantly over the weekends compared to working days. The number of exceedances of the WHO recommended limit value for PM2.5 (15 μg/m3) were 67 in Budapest and 46 in Debrecen, which corresponds to 73% and 50% of the sampling days, respectively. At the time of the exceedances the daily average temperature was below freezing. The average PM2.5/PM10 ratio was 70% and 75% for the two sites, indicating the dominance of the fine fraction aerosol particles during the study period. Elements of natural origin (Al, Si, Ca, Ti, Mn, Fe, Ba) and chlorine were found to be dominant in the coarse fraction, while elements of anthropogenic origin (S, K, Cu, Zn, Pb) were characteristic to the fine fraction. Similar concentrations were measured in the two cities in the case of S which originates from regional transport and K which serves as a tracer for biomass combustion. Traffic-related elements were present in 2–3 times higher concentrations in Budapest. The episodic peaks in the Cl time series could be attributed to salting after snowfalls. The following sources of APM pollution were identified by using the EPA Positive Matrix Factorization (PMF) 5.0 receptor model: soil, traffic, road dust, secondary sulfate, biomass burning, and de-icing of streets. On polluted days when the PM2.5 concentration exceeded the 25 μg/m3 value the contribution of secondary sulfate, domestic heating, and traffic increased significantly compared to the average. On weekends and holidays the contribution of soil and traffic decreased. The main pollution sources and their contributions were similar to the ones in other cities in the region. Comparing our findings to results from winter 2015 it can be concluded that while the PM2.5 pollution level remained almost the same, a significant increase in the contribution of biomass burning was observed in both cities from 2010 to 2015, indicating a change of heating habits.

Predicting intraurban airborne PM1.0-trace elements in a port city: Land use regression by ordinary least squares and a machine learning algorithm

Airborne particulate matter (PM) has been associated with cardiovascular and respiratory morbidity and mortality, and there is some evidence that spatially varying metals found in PM may contribute to adverse health effects. We developed spatially refined models for PM trace elements using ordinary least squares land use regression (OLS-LUR) and machine leaning random forest land-use regression (RF-LUR). Two-week integrated measurements of PM_1.0 (median aerodiameter < 1.0 μm) were collected at 50 sampling sites during fall (2010), winter (2011), and summer (2011) in the Halifax Regional Municipality, Nova Scotia, Canada. PM_1.0 filters were analyzed for metals and trace elements using inductively coupled plasma-mass spectrometry. OLS- and RF-LUR models were developed for approximately 30 PM_1.0 trace elements in each season. Model predictors included industrial, commercial, and institutional/ government/ military land use, roadways, shipping, other transportation sources, and wind rose information. RF generated more accurate models than OLS for most trace elements based on 5-fold cross validation. On average, summer models had the highest cross validation R² (OLS-LUR = 0.40, RF-LUR = 0.46), while fall had the lowest (OLS-LUR = 0.27, RF-LUR = 0.31). Many OLS-LUR models displayed overprediction in the final exposure surface. In contrast, RF-LUR models did not exhibit overpredictions. Taking overpredictions and cross validation performances into account, OLS-LUR performed better than RF-LUR in roughly 20% of the seasonal trace element models. RF-LUR models provided more interpretable predictors in most cases. Seasonal predictors varied, likely due to differences in seasonal distribution of trace elements related to source activity, and meteorology.

Role of ammonia in secondary inorganic aerosols formation at an ammonia-rich city in winter in north China: A comparative study among industry, urban, and rural sites

Ammonia is essential for the generation of secondary inorganic aerosols (SIA) in particulate matter, which affects severely the air quality in north China. In this study, PM_2.5 sampling was conducted as well as gaseous pollutant concentration and meteorological parameters were measured from November 2017 to January 2018. PM_2.5 concentration was highest in the industrial site (94.8 ± 41.7 μg m^-3), followed by urban (40.9 ± 24.1 μg m^-3) and rural (35.6 ± 20.3 μg m^-3) sites. The mass ratio of NO₃^-/SO₄^2- exhibited clear site variations, with the highest average value of 1.2 was found at the urban site, likely due to the dense traffic volume resulting in higher emissions of NO₂, and the lowest value of 0.9 at the industry site. The presence of Excess-NHx (E-NHx), raising the pH 24 by 1.4, 1.3, and 1.4 units in industry, urban, and rural sites, respectively, might be vital for raising the aerosol pH. Correlation coefficients of Nitrogen oxidation rate (NOR, NOR = [NO₃^-]/[NO₃^-] + [NO₂]) vs. Photochemical oxidants (O_x, NO₂ +O₃ in our study) and NOR vs. aerosol water content (AWC) at three sites were implied that both homogeneous and heterogeneous reactions occurred for nitrate formation in industry site, while heterogeneous reactions were dominant in urban and rural sites. Oxidation rates were most sensitive to the variation of E-NHx concentration at rural site, followed by the urban and industry sites, which was shown by the fact that the increase in E-NHx concentration by 1.0 μg m^-3 increased the SIA concentration by 1.21, 1.02, and 0.37 μg m^-3 at rural, urban, and industry sites, respectively. With the increase in NH_x emissions at present, the role of NH_x in SIA formation at ammonia-rich atmosphere requires more attention, especially in the less-noticed rural areas.

The impact of stay-home policies during Coronavirus-19 pandemic on the chemical and toxicological characteristics of ambient PM2.5 in the metropolitan area of Milan, Italy

The goal of this study was to characterize changes in components and toxicological properties of PM2.5 during the nationwide 2019-Coronavirus (COVID-19) lockdown restrictions in Milan, Italy. Time-integrated PM2.5 filters were collected at a residential site in Milan metropolitan area from April 11th to June 3rd at 2020, encompassing full-lockdown (FL), the followed partial-lockdown (PL2), and full-relaxation (FR) periods of COVID-19 restrictions. The collected filters were analyzed for elemental and organic carbon (EC/OC), water-soluble organic carbon (WSOC), individual organic species (e.g., polycyclic aromatic hydrocarbons (PAHs), and levoglucosan), and metals. According to online data, nitrogen dioxide (NO2) and benzene (C6H6) levels significantly decreased during the entire COVID-19 period compared to the same time span in 2019, mainly due to the government-backed shutdowns and curtailed road traffic. Similarly, with a few exceptions, surrogates of tailpipe emissions (e.g., traffic-associated PAHs) as well as re-suspended road dust (e.g., Fe, Mn, Cu, Cr, and Ti) were relatively lower during FL and PL2 periods in comparison with year 2019, whereas an increasing trend in mass concentration of mentioned species was observed from FL to PL2 and FR phases due to the gradual lifting of lockdown restrictions. In contrast, comparable concentrations of ambient PM2.5 and black carbon (BC) between lockdown period and the same time span in 2019 were attributed to the interplay between decreased road traffic and elevated domestic biomass burning as a result of adopted stay-home strategies. Finally, the curtailed road traffic during FL and PL2 periods led to ~25% drop in the PM2.5 oxidative potential (measured via 2',7'-dichlorodihydrofluorescein (DCFH) and dithiothreitol (DTT) assays) with respect to the FR period as well as the same time span in 2019. The results of this study provide insights into the changes in components and oxidative potential of PM2.5 in the absence of road traffic during COVID-19 restrictions.

Particulate matter emission sources and meteorological parameters combine to shape the airborne bacteria communities in the Ligurian coast, Italy

Aim of the present study is to explore how the chemical composition of particulate matter (PM) and meteorological conditions combine in shaping the air microbiome in Savona (Italy), a medium-size, heavily inhabited urban settlement, hosting a wide range of industrial activities. In particular, the air microbiome and PM₁₀ were monitored over six months in 2012. During that time, the air microbiome was highly dynamic, fluctuating between different compositional states, likely resulting from the aerosolization of different microbiomes emission sources. According to our findings, this dynamic process depends on the combination of local meteorological parameters and particle emission sources, which may affect the prevalent aerosolized microbiomes, thus representing further fundamental tools for source apportionment in a holistic approach encompassing chemical as well as microbiological pollution. In particular, we showed that, in the investigated area, industrial emissions and winds blowing from the inlands combine with an airborne microbiome which include faecal microbiomes components, suggesting multiple citizens' exposure to both chemicals and microorganisms of faecal origin, as related to landscape exploitation and population density. In conclusion, our findings support the need to include monitoring of the air microbiome compositional structure as a relevant factor for the final assessment of local air quality.

May SARS-CoV-2 Diffusion Be Favored by Alkaline Aerosols and Ammonia Emissions?

Ammonia is a common factor linking air in bat caves and air pollution in the proximity of agricultural fields treated with livestock farming sewage and slaughterhouses, where important clusters of COVID-19 have recently been reported all over the world. Such a commonality has a further connection with the known behavior of some viruses of the coronavirus family, such as the murine hepatitis virus, whose spike glycoprotein (S) can be triggered to a membrane-binding conformation at pH 8.0. Within the airborne route of virus transmission, with particular relevance for crowded and enclosed environments, these observations have prompted a hypothesis that may represent a contributing cause to interpret the geographical variability of the virus diffusion and the surging rise of COVID-19 cases in slaughterhouses all over the world. The hypothesis is that, in these environments, the SARS-CoV-2 S protein may find on a fraction of the airborne particles an alkaline pH, favorable to trigger the conformational changes, needed to induce the fusion of the viral envelope with the plasma membrane of the target cells.

Sustainable Development of the Historic Centre of Naples: The Impact of Vehicular Traffic and Food Service Business on Air Quality

Monitoring campaigns were carried out to assess the impact of vehicular traffic and food service business on the air quality in the historic centre of Naples. These campaigns monitored fine particles (FPs) from 20 to 1000 nm, using a condensation particle counter (CPC) in four connected streets, during a period of four weeks, from 7 November to 7 December 2019. Two streets were pedestrian only, while the others had average traffic. The following variables were considered while analysing the data—street geometry, and traffic and food service business emissions. The results showed prevalent air contamination, with some critical situations. The FP concentration values in the pedestrian streets were similar to the average values measured at the roadside of other European cities. However, the FP concentration values measured on the streets with average traffic, were twice that of their European counterparts. Spatial maps of FP concentration were produced to assess the impact of food service business emissions at the street level. The maps showed an insignificant contribution to FP pollution. However, it must be noted that emissions of the food service businesses were not measured at the roof top level in this study. The aspect ratio (H/W) played a relevant role on FP concentration, as an increase in aspect ratio correlated to an increase in FP concentration. These findings showed critical preliminary information for the sustainable development of the historic centre of Naples, which should be confirmed through a long-term monitoring campaign.

Organic molecular markers and source contributions in a polluted municipality of north-east Italy: Extended PCA-PMF statistical approach

Exceeding the maximum levels for environmental pollutants creates public and scientific interest for the environmental and human health impact it may have. In Northern Italy, the Po Valley, and in particular the Veneto region, is still a hotspot for air quality improvement. Several monitoring campaigns were carried out in this area to acquire information about sources of pollutants which are considered critical. For the first time, a deep study of the aerosol organic fraction was performed in the town Sernaglia della Battaglia, nearby Treviso. During three seasons of 2017, PM₁ and PM_2.5 samples were collected simultaneously. Organic molecular markers have been analyzed by in-situ derivatization thermal desorption gas chromatography time-of-flight mass spectrometry (IDTD-GC-TOFMS). Alkanes, polycyclic aromatic hydrocarbons, oxi-polycyclic aromatic hydrocarbons, anhydrous sugars, resins acids, triterpenoids, and acids were considered. The organic chemical composition has been analyzed based on seasonal variation and source contributions. Principal Component Analysis (PCA) and Positive Matrix Factorization (PMF) have been combined to deeply investigate the main sources of particulate organic matter. On the one hand, PCA evaluates the correlations between the organic markers and their seasonal distribution. On the other hand, the source contributions to aerosol composition are estimated by PMF. Four main emission sources were found by PMF: solid fuel combustion (coal, wood), combustion of petroleum distillates (gas and fuel oil) and exhaust gases of vehicles, industrial combustion processes, home heating, and forest fires are evaluated as the most important sources for the air quality and pollution in this municipality of Northern Italy.