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Filter-collected aerosol samples in the PM 1 and PM 10 fractions and particle number concentration were measured during experimental campaigns in a rural area near Bologna (Italy) in the periods 10–21 February 2014 and 19–30 May 2014. Ice nuclei particle (INP) concentrations measured off-line showed prevalently higher average values in the morning with respect to the afternoon, in the PM 1 fraction with respect to PM 1–10 (with the exception of the first campaign, at S w = 1.01), and at water saturation ratio S w = 1.01 with respect to S w = 0.96. The aerosol in the coarse size range (1–10 μm) contributed significantly to the total INP concentration. In the first campaign, the average INP concentration in the coarse fraction was 80% of the total in the morning and 74% in the afternoon, at S w = 1.01. In the second campaign, the contribution of the coarse size fraction to the INP number concentration was lower. On the whole, the results showed that the freezing activity of aerosol diameters larger than 1 μm needs to be measured to obtain the entire INP population. Sahara dust events (SDEs) took place during both campaigns, in the periods 17–20 February and 21–23 May 2014. Results show that the averaged particle number concentration was higher during SDE than during no-Saharan dust events. A low correlation between INP and total aerosol number concentration was generally measured, except for SDEs observed in February, in which the correlation coefficient between aerosol concentration in the coarse fraction and INP in the same range, at water supersaturation, was about 0.8. Precipitation events influenced the aerosol concentration. In the February campaign, lower values of INP and particle concentrations were measured in case of heavy rain events. During the May campaign, an average number concentration of the aerosol in the range 0.5–10 μm was slightly higher than on days when no precipitation was measured, the rainfall intensity being low. Only in a few cases did we note a sharp drop in INP in the PM 10 fraction at S w = 1.01 (26 May, 8 a.m. and 1 p.m.; 27 May, 1 p.m.). [ABSTRACT FROM AUTHOR]

For the first time, falling ice crystals were collected on glass slides covered with a thin layer of 2% formvar in chloroform at the Dome Concordia site (Dome C), Antarctica. Samplings were performed in the framework of the 27th Italian Antarctica expedition of the Italian National Program for Research in Antarctica in the period 21 February–6 August 2012. Events of clear-sky precipitations and precipitations from clouds were considered and the replicas obtained were examined under Scanning Electron Microscope (SEM). Several shapes of ice crystals were identified, including “diamond dust” (plates, pyramids, hollow and solid columns), and crystal aggregates varying in complexity. Single events often contained both small (10 μm to 50 μm) and large (hundreds of microns) crystals, suggesting that crystals can form simultaneously near the ground (height of a few hundred metres) and at higher layers (height of thousands of metres). Images of sampled crystal replicas showed that single bullets are not produced separately, but by the disintegration of combinations of bullets. Rimed ice crystals were absent in the Dome C samples, i.e. the only mode of crystal growth was water vapour diffusion. On considering the aerosol in the sampled crystals, we reached the conclusion that inertial impaction, interception and Brownian motion were insufficient to explain the scavenged aerosol. We therefore presume that phoretic forces play a role in scavenging during the crystal growth process. [ABSTRACT FROM AUTHOR]

The paper provides a review of past and a few new measurements of Ice-forming Nuclei (IN) in Antarctica. The few available published data were mostly obtained adopting different devices and methods and for a limited period of time. Consequently, data are scattered and give an incomplete picture of the Antarctic situation. It should be pointed out, however, that ice nucleation is an intricate process, depending on many parameters (supersaturation relative to ice and water, aerosol physical–chemical properties, possible conditioning and preactivation of particles, different modes of nucleation). Therefore, the uncertainty does not concern the Antarctic continent alone, but all measurements performed world-wide. A comparison of the published data can be made between Saxena and Weintraub (1988) at Palmer Station, and Ardon-Dryer et al. (2011) at the South Pole, as both studies measured IN in the immersion mode, even if at different temperature. Saxena and Weintraub (1988) obtained in three filters IN concentrations of about 104 m−3 at T=−6°C, −11°C and −13°C, and 103 m−3 at T=−17°C, in an additional filter (February–December 1983). At the South Pole Ardon-Dryer et al. (2011) obtained a concentration of about 5×102 m−3 at T=−19°C, and the IN concentration increased until about 40×103 m−3 at the activation temperature of −26°C. Such values are higher than those measured by Bigg (1973) near Antarctica, using a thermal diffusion chamber (deposition or deposition–condensation modes). IN concentrations measured at Terra Nova Bay are lower than those reported above, and are comparable to values reported for the Scott Base, Byrd Station and cruises at latitude 60°–70° S. [ABSTRACT FROM AUTHOR]

Abstract: During austral summer 2006, in the framework of the XXII Italian Antarctic expedition of PNRA (Italian National Program for Research in Antarctica), aerosol particle number size distribution measurements were performed in the 10–500 range nm over the Nansen Ice Sheet glacier (NIS, 74°30′ S, 163°27′ E; 85m a.s.l), a permanently iced branch of the Ross Sea. Observed total particle number concentrations varied between 169 and 1385cm−3. A monomodal number size distribution, peaking at about 70nm with no variation during the day, was observed for continental air mass, high wind speed and low relative humidity. Trimodal number size distributions were also observed, in agreement with measurements performed at Aboa station, which is located on the opposite side of the Antarctic continent to the NIS. In this case new particle formation, with subsequent particle growth up to about 30nm, was observed even if not associated with maritime air masses. [Copyright &y& Elsevier]

Laboratory generated aerosols and aerosol sampled in a field campaign were studied to assess the repeatability of heterogeneous ice activation processes and verify if the ice nuclei particles maintained their nucleating capability. Experiments were performed using a filter technique, i.e. aerosol particles were sampled on black-gridded cellulose nitrate membrane filters and assessed for ice nucleating particles in a dynamic filter-processing chamber at our ISAC-CNR laboratory. The laboratory investigations used Arizona Test Dust (ATD) generated by nebulizing a suspension of ATD. After nebulization, the wet aerosol in the carrier gas was dried and then sampled on a filter. Aerosol field sampling (size range PM1 and PM10) was carried out in the Arctic (Ny-Ålesund, Svalbard) from 12 to 23 April 2019. The activation processes were repeated twice for each filter at temperatures of −22 °C and −18 °C. For aerosol, ATD runs were performed only in conditions of supersaturation (saturation ratio S w = 1.02), while for the Arctic aerosol, conditions below saturation were also considered (S w = 0.96). The experiments showed that approximately 40% of the ATD particles maintain their initial nucleating efficiency, both at T = −22 °C and − 18 °C, and at S w = 1.02, i.e. in the condensation freezing mode. The percentage of repeatability was higher for ATD with respect to the Artic-sampled aerosol processed in the condensation mode. This may depend on greater particle morphology variation of the mixed organic-inorganic aerosol due to the hydration and dehydration cycle. • Experiments showed that about 40% of ATD particles maintains the nucleating efficacy. • The repeatability was higher for ATD with respect to aerosol sampled in Arctic. • Variation of ice nucleating capability of the aerosol has atmospheric implication. • The ice nucleation shows both stochastic and deterministic behavior. [ABSTRACT FROM AUTHOR]

In this work, the ice nucleating effectiveness of Arizona Test Dust (ATD), bare and coated with NaCl, not examined in previous published papers, was investigated. The ATD, NaCl coated ATD, and NaCl aerosols were generated by nebulizing water suspensions of bare ATD, ATD-NaCl and NaCl solution. Dried aerosols were sampled on black-gridded cellulose nitrate membrane filters for ice nuclei assessment through a Dynamic Filter Processing Chamber device (DFPC). After water evaporation ATD-NaCl droplets gave rise to ATD particles coated with NaCl. Processing of filters was performed at −22 °C and − 18 °C, under sub- and super-saturated conditions (water saturation ratio S w < 1 and S w > 1, respectively). Additional experiments were performed by modifying the storage conditions of the filters to simulate variation of atmospheric conditions, i.e. air temperature and relative humidity. For this purpose, the filters were housed in Petri dishes, with silica gel, at +10 °C and −10 °C. As silica gel can desorb water from the aerosol capillary at low temperatures, storage conditions with and without silica gel can simulate the aerosol pre-activation atmospheric process. The highest activated fraction (AF) and ice-active surface site density (n s) values were obtained for ATD at −22 °C and S w = 1.02. Results showed a decrease in the AF and n s between bare and ATD coated with NaCl both at S w = 1.02 and S w = 0.96 and for filters stored in the presence of silica gel. The results obtained show the great influence exerted by NaCl coated insoluble aerosol on the ice nucleation. • Results show a decrease in ice nucleation efficiency in case of NaCl coated ATD. • These results extend toward higher temperatures previous laboratory studies. • Preactivation process was simulated by storing the filters in low RH conditions. • Activated fraction increases from sub to super-saturated water conditions. [ABSTRACT FROM AUTHOR]

Optical detectors for atmospheric aerosol concentration measurements are often used in air quality applications given their potentialities for online measurements of air quality parameters at high temporal resolution. In this work the performances of different optical aerosol detectors used in air quality applications have been tested and compared for urban background aerosol conditions. Simultaneous measurements of aerosol number concentrations, size distributions and mass concentrations were taken in two different periods: November 2013 – February 2014 and May–June 2014 at an urban background site in Lecce (Southeastern Italy). Measurements were carried out using an OPC Grimm (mod. 1.109), an OPC FAI (Multichannel Monitor) and an optical photometer Mie pDR-1200. Good correlation, with determination coefficients R 2 larger than 0.93 were found between particle number concentrations measured by the two OPCs both in accumulation (0.28–0.90 μm for FAI and 0.29–0.90 μm for Grimm) and coarse modes (1.10–10 μm for FAI and 1.15–11.25 μm for Grimm). Absolute counting for the accumulation fraction shows that Grimm OPC detects more particles (about 10%) than FAI OPC at concentration higher than 200,000 particles/L in condition of high RH. This could be due to the changes of the optical properties of particles in high RH conditions visible even if the inlets of the two instruments are conditioned for lowering RH in sampled air. The differences in the absolute counting of the coarse fraction does not seems to be related to RH effects. The performances in evaluating mass concentrations PM10, and PM2.5 were evaluated comparing OPCs and pDR-1200 outputs with reference gravimetric and β-ray methods (that appeared to be essentially equivalent). Good agreement between Grimm OPC and SWAM is found both in PM10 and PM2.5 fractions while FAI OPC revealed greater discrepancy and scatter with respect to reference measurements. The performances of the pDR-1200 photometer were lower with respect to the OPCs with a larger influence of RH and optical properties of particles. The analysis of diurnal average trends in number and mass concentrations as well as the high temporal resolution responses of the instruments showed that optical detectors could be very useful to investigate atmospheric aerosol for air quality applications and to individuate and investigate specific pollution events. However, especially if they are used for evaluating mass concentrations (PM1, PM2.5 or PM10), it is necessary to take into account RH effects (even if the inlet are conditioned) and, possibly, use optical detectors together with reference gravimetric or β-ray methods to check their response in the effective operative conditions. [ABSTRACT FROM AUTHOR]

Abstract: The work presents the results of an experimental campaign performed at the Drop Tower Facility (Bremen) in microgravity conditions, concerning the scavenging process of an evaporating single droplet in stationary conditions. In the experimental conditions the thermo- and diffusiophoretic forces are the only ones that can determine the scavenging of the aerosol. The research is finalized to help solve the open question concerning the contribution of thermo- and diffusiophoretic forces in aerosol scavenging process due to cloud droplets. Although earlier theoretical and experimental papers have addressed this problem, the results are contradictory and inconclusive. As phoretic forces depend on aerosol diameter and water vapour pressure gradient, experiments were performed by changing the aerosol diameter (range 0.4μm–2μm) and the water vapour gradient. The experimental results show a prevalence of the diffusiophoretic over thermophoretic force, for the considered aerosol. The measured values of the particle velocities due to phoretic forces increase with increasing aerosol diameter and vapour pressure gradient. [Copyright &y& Elsevier]

Measurement campaigns at the high mountain Observatory Mt. Cimone (CMN; 2165 m a.s.l.) were performed during May 2014 and October 2015. The concentration of Ice Nucleating Particles (INPs) were measured offline with a dynamic filter processing chamber (DFPC), in the deposition and condensation mode, after collecting PM 1 and PM 10 aerosol samples. Presented INP data are the first ever published for a high mountain site in the Mediterranean basin. During the May campaign, parallel INP measurements were also carried out at San Pietro Capofiume (SPC), a low altitude rural background area within the Po Valley basin, by the same offline technique. The average INP PM10 concentration at CMN was 86 m −3 (saturation ratio S w = 1.01; T = −18 °C) during the May 2014 campaign, while it was 171 m −3 at SPC, in the same period. A lower average INP PM10 concentration was observed at CMN during October 2015 (43 m −3 ). A significantly higher activated fraction (AF) characterized the October 2015 campaign, suggesting that the seasonal changes in the aerosol sources have an impact on the INP efficiency of the aerosol at CMN. Super-micrometer INP contributed for ∼30% of total INP in the May 2014 campaign, at both sites, and for ∼70% in the October 2015 campaign, showing the importance of coarse particles in the INP population. The analysis of meteorological parameters, gaseous tracers concentrations and backwards trajectories suggests that the INP population at CMN is contributed by transport processes occurring at diverse spatial scales, from the local to the synoptic scale. During the Saharan Dust transport Event observed in May 2014, a reduction of the AF was observed, suggesting, for this case, a limited ice nucleating activity for Saharan dust particles. This may be due to physico-chemical aging of the Saharan dust particles during transport or to the relatively high activation temperature at which the experiments were performed in this study. [ABSTRACT FROM AUTHOR]

Indoor air samples from libraries and archives in Florence, Italy, were collected and analysed for a variety of volatile organic compounds. The aim was to perform a characterisation of the indoor air quality, and try to elucidate if there are VOCs that may cause or result from the determination of the cultural heritage institutions. All compounds of interest were regularly detected, with BTEXs (Benzene, Toluene, Ethylbenzene, Xylenes) being the most abundant and followed by cyclic volatile methylsiloxanes, aldehydes, terpenes and organic acids. The prevalence and qualitative characteristics, such as concentrations, profiles and indoor/outdoor ratios of BTEXs underline the important influence of the outdoor air infiltrations on the indoor air concentrations. Acetic acid that is a substance that can oxidise books and other exposed objects was detected at concentrations ranging between 1.04 and 18.9 μg m − 3 , while furfural, that is a known marker of paper degradation, was constantly present at concentrations that ranged between 5.26 and 32.6 μg m − 3 . This work shows the importance that indoor air quality monitoring campaigns can have in order to give early warning to cultural heritage institution managers about the impact that indoor air quality can have on exposed and/or preserved objects. [ABSTRACT FROM AUTHOR]

Cellulose acetate (CA) nanofibers were prepared via electrospinning to obtain a high quality factor (QF) fibrous mat for aerosol particle filtration. To this purpose, special attention was paid to the substrate material used to collect the nanofibers. Different materials (glassine paper, Lyocell, nylon grids) were investigated for use as substrates in the membrane spinning process. Membrane and membrane fiber morphologies were characterized by optical microscope and scanning electron microscope (SEM) analyses. Results show that the arrangement of the membrane fibers is directly correlated to the morphology of the collecting substrate material. Experiments shows that the electrospun nanofiber web tends to recreate the specific character of the supporting textile texture. A support with a pronounced bi-dimensional structure should be preferred. A regular grid, made of nylon, is selected for the composition with CA nanofibres. By maintaining the same support, various electrospinning parameters such as the spinning solution CA concentration (14 wt%, 18 wt%) and spinning volume (15–120 μL) of the membranes are tested in terms of air filtration performance. Filtration tests are performed by measuring the filter penetration against neutralized aerosol particles. Basis weight, solid volume fraction and thickness parameter were investigated to find the best arrangement. The filtration efficiency of stacked layers is analyzed at variable thickness of the building block element. An electrospun membrane of above 60 μm thickness, combined with the selected substrate, increases the QF and improve its reproducibility. The QF can be further increased with an optimized porosity of the nylon substrate. The best QF of 0.080±0.050 Pa −1 at 300 nm was obtained by spinning a 14 wt% CA solution in an acetone- DMSO-acetic acid solvent mixture on a nylon grid with 100 μm mesh size producing fleeces with a very low pressure drop (7 Pa). Thermogravimetric analyses (TGA) and SEM imaging demonstrated the stability of the composite filter morphology up to 200 °C. [ABSTRACT FROM AUTHOR]

Although biogas production can have some benefits, there is a research gap on potential influence of biogas plant emissions on local air quality, thus an accurate and comprehensive evaluation of impacts of this technology is needed. This study deals with this issue by means of a characterisation of air pollution near an industrial area including a biogas production (from biomass) and combustion plant located in South Italy. The methodology consists in advanced statistical analysis on concentration of gaseous pollutants, particles concentration and size distribution in number and mass, and PM 2.5 chemical composition. High-temporal resolution measurements, supported by ancillary meteorological parameters, and source apportionment of PM 2.5 using Positive Matrix Factorization (PMF) receptor model, are performed. The integrated approach provides the emissive picture consisting in different anthropogenic sources (i.e. traffic, biomass burning, and industrial facilities) with particular focus on biogas plant emissions. Results showed that CO and nitrogen oxides were influenced by vehicular traffic and biomass combustion, however, a contribution of the plant to NO was observed. SO 2 was influenced mainly by transport from the industrial zone, but a second local contribution compatible with the emissions of the biogas plant was detected. Number particle concentrations were analysed in four size ranges: nanoparticles (D < 0.05 μm), ultrafine particles (D < 0.3 μm), accumulation (0.3 < D < 1 μm) and coarse particles (D > 1 μm). Nanoparticles and ultrafine particles were mainly influenced by vehicular traffic and biomass burning, instead, a contribution of the plant was individuated in the accumulation mode. PMF5 identified the contribution of six sources: crustal (14.7% ± 2.1% of measured PM 2.5); marine aerosol (aged) (12.9% ± 2.3%); biomass burning (32.8% ± 1.4%); secondary sulphate (19.7% ± 2.4%); primary industrial emissions (5.4% ± 2.3%); traffic and secondary nitrate (17.0% ± 3.9%). The plant is likely to contribute to both sources, the industrial and the traffic plus secondary nitrate. Unlabelled Image • Air quality was investigated near a biogas production and combustion plant. • Biomass burning was the main source for CO, NO X , nanoparticles, and PM 2.5. • Plant's contribution to NO, SO 2 , accumulation mode particles and nitrate were found. • PM 2.5 source apportionment showed relevant secondary contributions. • Biogas plant contributes to specific odorous compounds like DMA in PM 2.5. [ABSTRACT FROM AUTHOR]