Towards a Formal Verification Methodology for Collective Robotic Systems

We introduce a UML-based notation for graphically modeling systems’ security aspects in a simple and intuitive way and a model-driven process that transforms graphical specifications of access control policies in XACML. These XACML policies are then translated in FACPL, a policy language with a formal semantics, and the resulting policies are evaluated by means of a Java-based software tool

High time-resolved multi-wavelength measurements of light absorption properties of atmospheric aerosol using a polar photometer

Black Carbon (BC) is the main absorber of solar radiation among the aerosol components, it influences cloud processes, and alters the melting of snow and ice cover. On global scale, it is currently identified as the second most important individual climate-warming component after CO2, but uncertainties on the radiative forcing related to BC-radiation interaction still cover more than one order of magnitude. Moreover, weakly absorbing organic material (brown carbon, BrC) in the form of particle coating or as particle as-is can be considered a further important contributor to aerosol absorption. The peculiarity of BrC is that it is very effective in the absorption of short-\u3bb radiation whereas its contribution to aerosol absorption is negligible in the red or near-IR bands. It is noteworthy that BC and BrC can also be used for source apportionment purposes (e.g. they can be helpful for the discrimination between fossil fuels combustion vs. biomass burning). Thus, work is currently ongoing to develop instrumentation able to give more and more detailed information on the absorption properties of atmospheric aerosol, possibly related to mixing and/or size information, and BC content. Moving in this frame, a multi-\u3bb polar photometer (PP_UniMI) has been developed at the Department of Physics of the University of Milan in the last years. The instrument is based on the measurement on the scattering plane of the light transmitted and scattered in the forward and back hemispheres by unloaded and loaded samples using a rotating photodiode. Data reduction aiming at the determination of the sample absorbance follows Petzold et al. (2004) and therein cited literature. In its original version (see details in Vecchi et al., 2013) the PP_UniMI allowed measuring aerosol deposited on 47 mm diameter filters at a single wavelength (\u3bb), then further upgraded to 4-\u3bb (870, 633, 532, 405 nm). In this work, we improved PP_UniMI to provide the absorption properties of the aerosol collected with high-time resolution using a streaker sampler. Such sampler collects aerosol segregated in two size-classes (fine and coarse) on a rotating frame with hourly resolution. The deposit corresponding to 1-hour sampling is collected on 1x8 mm2 streaks. To analyse such deposits, suitable pairs of lenses were used to reduce the spot-size down to about 1 mm diameter (see Figure 1). A 1-mm diameter pinhole was added to the set-up in order to ensure that the spot was small enough to allow the single-streak measurement. It is noteworthy that some laser sources are placed at 90\ub0 respect to the incident direction on the filter, thus mirrors are present in the set-up. The new set-up or the instrument was validated against independent measurements carried out using a Multi-Angle Absorption Photometer for what concerns the red-light results. The results presented here will include the validation of the instrumentation and the results of one-week winter campaign. Data reduction will aim at evidencing high time-resolved trends of multi-wavelength aerosol absorption. This is important both for gaining insight into aerosol absorption properties (still poorly known) and for source identification purposes

Saharan dust impact in central Italy: An overview on three years elemental data records

In southern European countries, Saharan dust may episodically produce significant increases of PM10, which may also cause the exceedance of the PM10 daily limit value established by the European Directive (2008/50/EC). The detection with very high sensitivity of all the elements that constitute mineral dust makes PIXE technique a very effective tool to assess the actual impact of these episodes. In this work, a review of long-term series of elemental concentrations obtained by PIXE has been accomplished with the aim of identifying the occurrence of Saharan dust transport episodes over long periods in Tuscany and characterising them in terms of composition and impact on PM concentration, tracing back their contribution to the exceedances of the PM10 limit value. The impact of the different Saharan intrusions on PM10 showed a very high variability. During the most intense episodes (which occurred with a frequency of few times per year) the calculated soil dust concentration reached values as high as 25\u201330 \u3bcg m 123, to be compared with background values of the order of 5 \u3bcg m 123. The Saharan dust contribution was decisive to cause the exceedance of the PM10 daily limit value in the 1\u20132% of the days considered in the present work

Nuclear techniques and the particulate matter pollution in big harbours

The impact of big harbours on the air quality is an important issue both from the environmental and the economical point of view. The harbour of Genoa is the largest in Italy and one of the major ports of the Mediterranean. We have determined the fraction of Particulate Matter (PM) concentration in town due to the heavy oil combustion of the diesel engines of the vessels in the harbour. This turned out to be 12% in PM10 and 25% in PM2.5 and PM1, with about 85% of the PM from this source concentrated in particles with aerodynamic diameter, Dae < 1 μm. We could also point out a link between concentration peaks of the tracers of heavy oil combustion (V and Ni) and the ferryboats traffic. The key tool in this work was the coupling between particular sampling devices and some Ion Beam Analysis (IBA) techniques, in particular Particle Induced X-ray Emission (PIXE), which belong to the broader category of nuclear techniques in applied physics

Exploiting multi-wavelength aerosol absorption coefficients in a multi-time resolution source apportionment study to retrieve source-dependent absorption parameters

In this paper, a new methodology coupling aerosol optical and chemical parameters in the same source apportionment study is reported. In addition to results on source contributions, this approach provides information such as estimates for the atmospheric absorption Angstrom exponent (alpha) of the sources and mass absorption cross sections (MACs) for fossil fuel emissions at different wavelengths. A multi-time resolution source apportionment study using the Multilinear Engine (ME-2) was performed on a PM10 dataset with different time resolutions (24, 12, and 1 h) collected during two different seasons in Milan (Italy) in 2016. Samples were optically analysed by an in-house polar photometer to retrieve the aerosol absorption coefficient b(ap) (in Mm 1) at four wavelengths (lambda = 405, 532, 635, and 780 nm) and were chemically characterized for elements, ions, levoglucosan, and carbonaceous components. The dataset joining chemically speciated and optical data was the input for the multi-time resolution receptor model; this approach was proven to strengthen the identification of sources, thus being particularly useful when important chemical markers (e.g. levoglucosan, elemental carbon) are not available. The final solution consisted of eight factors (nitrate, sulfate, resuspended dust, biomass burning, construction works, traffic, industry, aged sea salt); the implemented constraints led to a better physical description of factors and the bootstrap analysis supported the goodness of the solution. As for b(ap) apportionment, consistent with what was expected, biomass burning and traffic were the main contributors to aerosol absorption in the atmosphere. A relevant feature of the approach proposed in this work is the possibility of retrieving a lot of other information about optical parameters; for example, in contrast to the more traditional approach used by optical source apportionment models, here we obtained source-dependent alpha values without any a priori assumption (alpha biomass burning = 1:83 and alpha fossil fuels = 0:80). In addition, the MACs estimated for fossil fuel emissions were consistent with literature values. It is worth noting that the approach presented here can also be applied using more common receptor models (e.g. EPA PMF instead of multi-time resolution ME-2) if the dataset comprises variables with the same time resolution as well as optical data retrieved by widespread instrumentation (e.g. an Aethalometer instead of in-house instrumentation)

Characterization of aerosol sources in Le&#243;n (Spain) using Positive Matrix Factorization and weather types

A one-year aerosol sampling campaign, between 2016 and 2017, was conducted in a suburban area of León city, Spain. An association between the Positive Matrix Factorization (PMF) results and air masses through circulation weather types was carried out, through the construction of linear models from the PM10 concentrations and its chemical composition. The aerosol sources, identified by PMF six-factor solution, were: traffic (29%), aged sea salt (26%), secondary aerosols (16%), dust (13%), marine aerosol (7%) and biomass burning (3%). Traffic and secondary factors showed the highest PM10 contribution in the hybrid cyclonic types with wind component from the first and second quadrant. Anticyclonic types with wind component from the first quadrant exhibited high values of secondary, aged sea salt and dust factors. The highest contributions of the dust factor were also associated with northerly types. The linear models built for estimating the source apportionment of PM10, from aerosol chemical composition and geostrophic flow, showed positive coefficients for: westerly flows (WF) in marine factor, southerly flows (SF) in secondary and traffic factors, and shear southerly vorticities (ZS) in dust factor. Negative dependences were observed for ZS in aged sea salt factor and for SF in dust factor. The PM10 mass concentration calculated by the linear models and by the PMF model were strongly correlated. This can be very useful to determine the contribution of a specific source to PM10 in León, only by knowing some meteorological and chemical variables.publishe

Carbonaceous aerosol in polar areas: First results and improvements of the sampling strategies

While more and more studies are being conducted on carbonaceous fractions—organic carbon (OC) and elemental carbon (EC)—in urban areas, there are still too few studies about these species and their effects in polar areas due to their very low concentrations; further, studies in the literature report only data from intensive campaigns, limited in time. We present here for the first time EC–OC concentration long-time data records from the sea-level sampling site of Ny-Ålesund, in the High Arctic (5 years), and from Dome C, in the East Antarctic Plateau (1 year). Regarding the Arctic, the median (and the interquartile range (IQR)) mass concentrations for the years 2011–2015 are 352 (IQR: 283–475) ng/m3 for OC and 4.8 (IQR: 4.6–17.4) ng/m3 for EC, which is responsible for only 3% of total carbon (TC). From both the concentration data sets and the variation of the average monthly concentrations, the influence of the Arctic haze on EC and OC concentrations is evident. Summer may be interested by high concentration episodes mainly due to long-range transport (e.g., from wide wildfires in the Northern Hemisphere, as happened in 2015). The average ratio of EC/OC for the summer period is 0.05, ranging from 0.02 to 0.10, and indicates a clean environment with prevailing biogenic (or biomass burning) sources, as well as aged, highly oxidized aerosol from long-range transport. Contribution from ship emission is not evident, but this result may be due to the sampling time resolution. In Antarctica, a 1 year-around data set from December 2016 to February 2018 is shown, which does not present a clear seasonal trend. The OC median (and IQR) value is 78 (64–106) ng/m3; for EC, it is 0.9 (0.6–2.4) ng/m3, weighing for 3% on TC values. The EC/OC ratio mean value is 0.20, with a range of 0.06–0.35. Due to the low EC and OC concentrations in polar areas, correction for the blank is far more important than in campaigns carried out in other regions, largely affecting uncertainties in measured concentrations. Through the years, we have thus developed a new sampling strategy that is presented here for the first time: samplers were modified in order to collect a larger amount of particulates on a small surface, enhancing the capability of the analytical method since the thermo-optical analyzer is sensitive to carbonaceous aerosol areal density. Further, we have recently coupled such modified samplers with a sampling strategy that makes a more reliable blank correction of every single sample possible

Impact of vacuum cleaning on indoor air quality

Vacuum cleaning can be a household source of particulate matter (PM) both from the vacuum motor and from settled dust resuspension. Despite the evidence of this contribution to PM levels indoors, the effect of this source on PM composition is still unknown. In this study, four vacuum cleaners (washable filter bag less, wet, bagged and HEPA filter equipped robot) were tested for the emission rate of particulate mass and number. The detailed PM chemical characterisation included organic and elemental carbon, metals and organic speciation. PM10 emission rates from bagged vacuum operation were much higher (207 ± 99.0 μg min−1) compared with the ones obtained from wet (86.1 ± 16.9 μg min−1) and washable filter bag less vacuums (75.4 ± 7.89 μg min−1). Particle (8–322 nm) number emission rates ranged from 5.29 × 1011 (washable filter bag less vacuum) to 21.2 × 1011 (wet vacuum) particles min−1. Ratios of peak to background levels indicate that vacuuming can elevate the ultrafine particle number concentrations by a factor ranging from 4 to 61. No increase in PM mass or number concentrations was observed during the HEPA filter equipped vacuum operation. The increase in copper and elemental carbon PM10 contents during vacuuming suggested motor emissions. Organic compounds in PM10 included alkanes, PAHs, saccharides, phenolics, alcohols, acids, among others. However, it was not possible to establish a relationship between these compounds and vacuuming due to the vast array of possible household sources. The cancer risks associated with metals and PAH inhalation were negligible.publishe