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Numerous studies have shown negative health effects related to exposure to ambient particulate matter (PM), likely due to induced oxidative stress. In this study, we have examined ambient PM samples from Birr, a small (~5000 inhabitants) town in central Ireland, for their water-soluble DTT-based oxidative potential (OP_DTT) with a resolution of 6 h, together with online chemical characterization measurements, to assess the OP of organic aerosols, in particular from residential solid fuel burning. The OP_DTT normalized by the volume of sampled air shows a high variability, ranging from <0.1 to 3.8 nmol min−1 m−3, and a high correlation with PM mass. A lower variability was associated with the mass-normalized OP. Nevertheless, both tended to present higher values during night-time pollution episodes. Simple and multivariate linear regression approaches linked OP_DTT to residential solid fuel burning, and in particular to wood (~87%) and peat (~13%) combustion. The results of the present study show how residential solid fuel burning can have a severe impact on air quality, even in small towns, with potential negative health effects on the exposed population. [ABSTRACT FROM AUTHOR]

New particle formation (NPF) is a major source of aerosol particles and cloud condensation nuclei in the troposphere, playing an important role in both air quality and climate. Frequent NPF events have been observed in heavily polluted urban environments, contributing to the aerosol number concentration by a significant amount. The Po Valley region in northern Italy has been characterized as a hotspot for high aerosol loadings and frequent NPF events in southern Europe. However, the mechanisms of NPF and growth in this region are not completely understood. In this study, we conducted a continuous 2-month measurement campaign with state-of-the-art instruments to elucidate the NPF and growth mechanisms in northern Italy. Our results demonstrate that frequent NPF events (66 % of all days during the measurement campaign) are primarily driven by abundant sulfuric acid (8.5×106 cm -3) and basic molecules in this area. In contrast, oxygenated organic molecules from the atmospheric oxidation of volatile organic compounds (VOCs) appear to play a minor role in the initial cluster formation but contribute significantly to the consecutive growth process. Regarding alkaline molecules, amines are insufficient to stabilize all sulfuric acid clusters in the Po Valley. Ion cluster measurements and kinetic models suggest that ammonia (10 ppb) must therefore also play a role in the nucleation process. Generally, the high formation rates of sub-2 nm particles (87 cm -3 s -1) and nucleation-mode growth rates (5.1 nm h -1) as well as the relatively low condensational sink (8.9×10-3 s -1) will result in a high survival probability for newly formed particles, making NPF crucial for the springtime aerosol number budget. Our results also indicate that reducing key pollutants, such as SO 2 , amine and NH 3 , could help to substantially decrease the particle number concentrations in the Po Valley region. [ABSTRACT FROM AUTHOR]

New particle formation (NPF) is a major source of aerosol particles and cloud condensation nuclei in the troposphere, playing an important role in both air quality and climate. Frequent NPF events have been observed in heavily polluted urban environments, contributing to the aerosol number concentration by a significant amount. The Po Valley region in northern Italy has been characterized as a hotspot for high aerosol loadings and frequent NPF events in Southern Europe. However, the mechanisms of NPF and growth in this region are not completely understood. In this study, we conducted a continuous 2-month measurement campaign with state-of-the-art instruments to elucidate the NPF and the growth mechanisms in Northern Italy. Our results show that abundant sulfuric acid, ammonia and amines from agricultural activities may be the dominant components driving the frequent NPF events (66 % of all days during the measurement campaign) in this area. In contrast, organics seem to have a smaller role in cluster formation but contribute to the consecutive growth process. According to ion cluster measurements and kinetic model results, dimethylamine is not sufficient to stabilize all of the sulfuric acid during springtime in the Po Valley, suggesting that other amines and ammonia can also be involved. Generally, the high formation rates of sub-2 nm particles (87 cm−3 s−1) and nucleation mode growth rates (5.1 nm h−1) together with the relatively low condensational sink (8.9 × 10−3 s−1) will result in a high survival probability of newly formed particles, making NPF crucial for the springtime aerosol number budget in the Po Valley region. [ABSTRACT FROM AUTHOR]

The RHAPS (Redox-Activity And Health-Effects Of Atmospheric Primary And Secondary Aerosol) project was launched in 2019 with the major objective of identifying specific properties of the fine atmospheric aerosol from combustion sources that are responsible for toxicological effects and can be used as new metrics for health-related outdoor pollution studies. In this paper, we present the overall methodology of RHAPS and introduce the phenomenology and the first data observed. A comprehensive physico-chemical aerosol characterization has been achieved by means of high-time resolution measurements (e.g., number size distributions, refractory chemical components, elemental composition) and low-time resolution analyses (e.g., oxidative potential, toxicological assays, chemical composition). Preliminary results indicate that, at the real atmospheric conditions observed (i.e., daily PM1 from less than 4 to more than 50 μg m−3), high/low mass concentrations of PM1, as well as black carbon (BC) and water soluble Oxidative Potential (WSOP,) do not necessarily translate into high/low toxicity. Notably, these findings were observed during a variety of atmospheric conditions and aerosol properties and with different toxicological assessments. Findings suggest a higher complexity in the relations observed between atmospheric aerosol and toxicological endpoints that go beyond the currently used PM1 metrics. Finally, we provide an outlook to companion papers where data will be analyzed in more detail, with the focus on source apportionment of PM1 and the role of source emissions on aerosol toxicity, the OP as a predictive variable for PM1 toxicity, and the related role of SOA possessing redox-active capacity, exposure-response relationships for PM1, and air quality models to forecast PM1 toxicity. [ABSTRACT FROM AUTHOR]

Sub-Saharan Africa (SSA) is a global hot spot for aerosol emissions, which affect the regional climate and air quality. In this paper, we use ground-based observations to address the large uncertainties in the source-resolved emission estimation of carbonaceous aerosols. Ambient fine fraction aerosol was collected on filters at the high-altitude (2590 m a.s.l.) Rwanda Climate Observatory (RCO), a SSA background site, during the dry and wet seasons in 2014 and 2015. The concentrations of both the carbonaceous and inorganic ion components show a strong seasonal cycle, with highly elevated concentrations during the dry season. Source marker ratios, including carbon isotopes, show that the wet and dry seasons have distinct aerosol compositions. The dry season is characterized by elevated amounts of biomass burning products, which approach ∼95 % for carbonaceous aerosols. An isotopic mass-balance estimate shows that the amount of the carbonaceous aerosol stemming from savanna fires may increase from 0.2 µ g m -3 in the wet season up to 10 µ g m -3 during the dry season. Based on these results, we quantitatively show that savanna fire is the key modulator of the seasonal aerosol composition variability at the RCO. [ABSTRACT FROM AUTHOR]

The Po Valley (Italy) is a well-known air quality hotspot characterized by particulate matter (PM) levels well above the limit set by the European Air Quality Directive and by the World Health Organization, especially during the colder season. In the framework of Emilia-Romagna regional project "Supersito", the southern Po Valley submicron aerosol chemical composition was characterized by means of high-resolution aerosol mass spectroscopy (HR-AMS) with the specific aim of organic aerosol (OA) characterization and source apportionment. Eight intensive observation periods (IOPs) were carried out over 4 years (from 2011 to 2014) at two different sites (Bologna, BO, urban background, and San Pietro Capofiume, SPC, rural background), to characterize the spatial variability and seasonality of the OA sources, with a special focus on the cold season. On the multi-year basis of the study, the AMS observations show that OA accounts for averages of 45±8 % (ranging from 33 % to 58 %) and 46±7 % (ranging from 36 % to 50 %) of the total non-refractory submicron particle mass (PM 1 -NR) at the urban and rural sites, respectively. Primary organic aerosol (POA) comprises biomass burning (23±13 % of OA) and fossil fuel (12±7 %) contributions with a marked seasonality in concentration. As expected, the biomass burning contribution to POA is more significant at the rural site (urban / rural concentration ratio of 0.67), but it is also an important source of POA at the urban site during the cold season, with contributions ranging from 14 % to 38 % of the total OA mass. Secondary organic aerosol (SOA) contributes to OA mass to a much larger extent than POA at both sites throughout the year (69±16 % and 83±16 % at the urban and rural sites, respectively), with important implications for public health. Within the secondary fraction of OA, the measurements highlight the importance of biomass burning aging products during the cold season, even at the urban background site. This biomass burning SOA fraction represents 14 %–44 % of the total OA mass in the cold season, indicating that in this region a major contribution of combustion sources to PM mass is mediated by environmental conditions and atmospheric reactivity. Among the environmental factors controlling the formation of SOA in the Po Valley, the availability of liquid water in the aerosol was shown to play a key role in the cold season. We estimate that the organic fraction originating from aqueous reactions of biomass burning products ("bb-aqSOA") represents 21 % (14 %–28 %) and 25 % (14 %–35 %) of the total OA mass and 44 % (32 %–56 %) and 61 % (21 %–100 %) of the SOA mass at the urban and rural sites, respectively. [ABSTRACT FROM AUTHOR]

One of the most important natural aerosol systems at the global level is marine aerosol that comprises both organic and inorganic components of primary and secondary origin. The present paper reviews some new results on primary and secondary organic marine aerosol, achieved during the EU project MAP (Marine Aerosol Production), comparing them with those reported in the recent literature. Marine aerosol samples collected at the coastal site ofMaceHead, Ireland, show a chemical composition trend that is influenced by the oceanic biological activity cycle, in agreement with other observations. Laboratory experiments show that seaspray aerosol from biologically active sea water can be highly enriched in organics, and the authors highlight the need for further studies on the atmospheric fate of such primary organics. With regard to the secondary fraction of organic aerosol, the average chemical composition and molecular tracer (methanesulfonic-acid, amines) distribution could be successfully characterized by adopting a multitechnique analytical approach. [ABSTRACT FROM AUTHOR]

Nature-based solutions can represent beneficial tools in the field of urban transformation for their contribution to important environmental services such as air quality improvement. To evaluate the impact on urban air pollution of a CityTree (CT), an innovative wall-type green infrastructure in passive (deposition) and active (filtration) modes of operation, a study was conducted in a real urban setting in Modena (Italy) during 2017 and 2018, combining experimental measurements with modelling system evaluations. In this work, relying on the computational resources of CRESCO (Computational Centre for Research on Complex Systems)/ENEAGRID High Performance Computing infrastructure, we used the air pollution microscale model PMSS (Parallel Micro-SWIFT-Micro SPRAY) to simulate air quality during the experimental campaigns. The spatial characteristics of the impact of the CT on local air pollutants concentrations, specifically nitrogen oxides (NOx) and particulate matter (PM10), were assessed. In particular, we used prescribed bulk deposition velocities provided by the experimental campaigns, which tested the CT both in passive (deposition) and in active (filtration) mode of operation. Our results showed that the PM10 and NOx concentration reductions reach from more than 0.1% up to about 0.8% within an area of 10 × 20 m2 around the infrastructure, when the green infrastructure operates in passive mode. In filtration mode the CT exhibited higher performances in the abatement of PM10 concentrations (between 1.5% and 15%), within approximately the same area. We conclude that CTs may find an application in air quality hotspots within specific urban settings (i.e., urban street canyons) where a very localized reduction of pollutants concentration during rush hours might be of interest to limit population exposure. The optimization of the spatial arrangement of CT modules to increment the "clean air zone" is a factor to be investigated in the ongoing development of the CT technology. [ABSTRACT FROM AUTHOR]

Suspected detrimental health effects associated with ultrafine particles (UFPs) are impressive. However, epidemiological evidence is still limited. This is potentially due to challenges related to UFP exposure assessment and the lack of consensus on a standard methodology for UFPs. It is imperative to focus future health studies on those UFP metrics more likely to represent health effects. This is the purpose of this paper, where we extend the results obtained during the CARE ("Carbonaceous Aerosol in Rome and Environs") experiment started in 2017 in Rome. The major purpose is to investigate features of airborne UFPs associated with pro-inflammatory and oxidative responses. Aerosol chemical, microphysical, and optical properties were measured, together with the oxidative potential, at temporal scales relevant for UFPs (minutes to hours). The biological responses were obtained using both in-vivo and in-vitro tests carried out directly under environmental conditions. Findings indicate that caution should be taken when assessing health-relevant exposure to UFPs through the conventional metrics like total particle number concentration and PM2.5 and Black Carbon (BC) mass concentration. Conversely, we recommend adding to these, a UFP source apportionment analysis and indicators for both ultrafine black carbon and the size of particles providing most of the total surface area to available toxic molecules. [ABSTRACT FROM AUTHOR]

Soot particles form during combustion of carbonaceous materials and impact climate and air quality. When freshly emitted, they are typically fractal-like aggregates. After atmospheric aging, they can act as cloud condensation nuclei, and water condensation or evaporation restructure them to more compact aggregates, affecting their optical, aerodynamic, and surface properties. Here we survey the morphology of ambient soot particles from various locations and different environmental and aging conditions. We used electron microscopy and show extensive soot compaction after cloud processing. We further performed laboratory experiments to simulate atmospheric cloud processing under controlled conditions. We find that soot particles sampled after evaporating the cloud droplets, are significantly more compact than freshly emitted and interstitial soot, confirming that cloud processing, not just exposure to high humidity, compacts soot. Our findings have implications for how the radiative, surface, and aerodynamic properties, and the fate of soot particles are represented in numerical models. [ABSTRACT FROM AUTHOR]

Aerosol liquid water (ALW) influences aerosol radiative properties and the partitioning of gas-phase water-soluble organic compounds (WSOCg) to the condensed phase. A recent modeling study drew attention to the anthropogenic nature of ALW in the southeastern United States, where predicted ALW is driven by regional sulfate. Herein, we demonstrate that ALW in the Po Valley, Italy, is also anthropogenic but is driven by locally formed nitrate, illustrating regional differences in the aerosol components responsible for ALW. We present field evidence for the influence of controllable ALW on the lifetimes and atmospheric budgets of reactive organic gases and note the role of ALW in the formation of secondary organic aerosol (SOA). Nitrate is expected to increase in importance due to increased emissions of nitrate precursors, as well as policies aimed at reducing sulfur emissions. We argue that the impacts of increased particulate nitrate in future climate and air quality scenarios may be under predicted because they do not account for the increased potential for SOA formation in nitrate-derived ALW, nor do they account for the impacts of this ALW on reactive gas budgets and gas-phase photochemistry. [ABSTRACT FROM AUTHOR]

This paper synthesizes data on aerosol (particulate matter, PM) physical characteristics, which were obtained in European aerosol research activities at free-troposphere, natural, rural, near-city, urban, and kerbside sites over the past decade. It covers only two sites in the semi-arid Mediterranean area, and lacks data from Eastern Europe. The data include PM10 and/or PM2.5 mass concentrations, and aerosol particle size distributions. Such data sets are more comprehensive than those currently provided by air quality monitoring networks (e.g. EMEP, EUROAIRNET). Data available from 31 sites in Europe (called “The Network”) were reviewed. They were processed and plotted to allow comparisons in spite of differences in the sampling and analytical techniques used in various studies. A number of conclusions are drawn as follows:Background annual average PM10 and PM2.5 mass concentrations for continental Europe are 7.0±4.1 and 4.8±2.4 μg m−3, respectively.The EU 2005 annual average PM10 standard of 40 μg m−3 is exceeded at a few sites in The Network. At all near city, urban and kerbside sites, the EU 2010 annual average PM10 standard of 20 μg m−3, as well as the US-EPA annual average PM2.5 standard of 15 μg m−3 are exceeded. In certain regions, PM10 and PM2.5 in cities are strongly affected by the regional aerosol background.There is no “universal” (i.e. valid for all sites) ratio between PM2.5 and PM10 mass concentrations, although fairly constant ratios do exist at individual sites. There is no universal correlation between PM mass concentration on the one hand, and total particle number concentration on the other hand, although a ‘baseline’ ratio between number and mass is found for sites not affected by local emissions. This paper is the first part of two companion papers of which the second part describes chemical characteristics. [Copyright &y& Elsevier]

This paper synthesizes data on aerosol (or particulate matter, PM) chemical characteristics, which were obtained in European aerosol research activities at natural, rural, near-city, urban, and kerbside sites over the past decade. It includes only two (nearby) sites in the semi-arid Mediterranean area, and lacks data from Eastern Europe. PM chemical compositions are compared with the PM mass concentrations in PM10, PM2.5, and further size resolved PM fractions (chemical mass closure). Such data sets are more comprehensive than those currently provided by air quality monitoring networks (e.g. EMEP, EUROAIRNET). Data available from 24 sites in Europe were reviewed. They were processed and plotted to allow comparisons in spite of differences in the sampling and analytical techniques used in various studies. A number of conclusions are drawn among which are the following.Organic matter appears to be the major component of PM10 and PM2.5, except at natural and rural background sites, where sulphate contribution may be larger. Mineral dust shows up as a major component of PM10 at kerbside sites. Black carbon contributes 5–10% to PM2.5 and somewhat less to PM10 at all sites, including the natural background sites. Its contribution seems higher (15–20%) at some of the kerbside sites, but these data may be affected by analytical artefacts. On days when PM10 >50 μg m−3, nitrate concentrations can overtake organic matter concentrations in PM10 and PM2.5. High PM concentration episodes are often observed in cold periods, when the pollutant dispersion is least. Measurements indicate that the condensation in the particle phase of semi-volatile species like nitrate and (unspecified) organics is also favoured by cold temperatures. In particles with a diameter <150 nm (i.e., most atmospheric particles), organic matter and black carbon are by far the major components.More data are known to be available within the scientific community, which could enrich the present data set and strengthen the conclusions made above. Most of them are not made available yet. The investment in new approaches, which would bridge the technological gap between scientific measurements and regulatory monitoring networks, is strongly needed. [Copyright &y& Elsevier]

The increasing exposure to air pollutants associated with the world-wide process of urbanization is among the most important risk factors for human health. In this context, the development of green infrastructures has gained interest for providing new win-win solutions for improving air quality and urban climate. In the present work, we have characterized an innovative, engineered green infrastructure, the CityTree (CT), in a real urban setting. Abatement rate of priority pollutants (PMx, NOx, black carbon) by a CT unit was determined, during three intensive field campaigns in the city of Modena (Italy). The measurements of the air filtered through the CT (active mode) showed significant reductions in particulate matter concentration: 19–23% for PM 10 aerosol mass, 15–20% for PM 2.5 , 11–13% for PM 1 , 38% for ultrafine particle number concentration and 17% for black carbon concentration. The measurements in passive mode (with ventilation off) enabled the estimation of the deposition velocities of aerosol particles and gases onto the device surface. The average deposition velocities for PM 10 and NO x observed for the CT mosses fall in the range reported in the scientific literature for other types of green surfaces (e.g., grass lawns, hedges). A comparison of the pollutant removal efficiency between passive and active CT mode was performed. The aerosol removal efficiency of the CT resulted from ~3 to almost 20 times higher in filtration than in deposition mode, according to the selected aerosol parameter. These results indicate that moss bio-filters can be more effective in removing air pollutants than standard green infrastructures for in situ applications. Image 1 • Effectiveness of an innovative green wall (CityTree) in improving air quality was evaluated. • Air pollutants filtration efficiency (up to 38%) was calculated for a CityTree. • Air pollutants deposition velocity was measured at the both sides of the CityTree. • Active mode (filtration) system is more efficient than passive (deposition) mode. [ABSTRACT FROM AUTHOR]