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

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)

Optical properties of aerosol particles over the Amazon rain forest: From background to biomass burning conditions

Atmospheric aerosols over the Amazon rainforest are strongly influenced by biomass burning activities in the southern regions of the Amazon Basin between July and October. This implies a complete change of the physical and chemical aerosol properties from the wet season, which is dominated by Primary Biological Aerosol Particles (PBAP) and biogenic secondary organic aerosols. Biomass burning emissions are highly loaded with light-absorbing aerosols, like black and brown carbon (BC and BrC, respectively). The latter one consists of a fraction of organic carbon that is able to absorb visible radiation (Andreae and Gelencs\ue9r, 2006). BrC is a strong absorber at near-UV to UV wavelengths. Therefore, light absorption by this component is wavelength dependent. This wavelength dependency, expressed as the absorption \uc5ngstr\uf6m exponent (AAE), has been used as a parameter to estimate the influence of biomass burning aerosols to total aerosol light absorption. However, the biogenic BrC contribution remains to be studied and could be significant under pristine conditions. The measurements presented here were carried out at the Amazon Tall Tower Observatory (ATTO), located 150 km NE of the city of Manaus, in the Uatum\ue3 Sustainable Development Reserve in Amazonas State, Brazil. The aerosol inlet (60 m high, 2.5 cm diameter) is installed on an 81-m triangular mast. The measurement period, from June to September 2014, includes the wetto- dry transition season (June-July) and part of the dry season (August and beginning of September). The optical properties were measured online by different instruments: 3-wavelengths nephelometer, Multi-Angle Absorption Photometer (MAAP), Single Particle Soot Photometer (SP2) and a 7-wavelength Aethalometer. Additionally, MAAP filter samples were analyzed by the Multi-Wavelength Absorbance Analyzer (MWAA) (Massab\uf2 et al, 2013), as well as levoglucosan analysis was carried out for filters collected between 18-22 August 2014. The average light absorption coefficient at 637 nm was 1.0 \ub1 0.6 Mm-1 and 5.5 \ub1 3.9 Mm-1, during the wet-to-dry transition and the dry season, respectively. Here we concentrate on measurements during 18-22 August 2014 (Figure 1) when a high absorption coefficient was measured at 637 nm, averaging 10 \ub1 3 Mm-1. The AAE calculated from MWAA measurements increased from less than 1.0 to values higher than 1.4, indicating the presence of BrC aerosol particles. This period is characterized by a long-range transport of biomass burning aerosol (confirmed by backward trajectory analysis). Levoglucosan analysis reveals significantly increased concentration but is still relatively low compared to measurements close to the source (Graham et al, 2002). Nevertheless, AAE and levoglucosan concentration show a significant correlation (r\ub2 > 0.9)

Trace Metals in Soot and PM2.5from Heavy-Fuel-Oil Combustion in a Marine Engine

Heavy fuel oil (HFO) particulate matter (PM) emitted by marine engines is known to contain toxic heavy metals, including vanadium (V) and nickel (Ni). The toxicity of such metals will depend on the their chemical state, size distribution, and mixing state. Using online soot-particle aerosol mass spectrometry (SP-AMS), we quantified the mass of five metals (V, Ni, Fe, Na, and Ba) in HFO-PM soot particles produced by a marine diesel research engine. The in-soot metal concentrations were compared to in-PM2.5measurements by inductively coupled plasma-optical emission spectroscopy (ICP-OES). We found that <3% of total PM2.5metals was associated with soot particles, which may still be sufficient to influence in-cylinder soot burnout rates. Since these metals were most likely present as oxides, whereas studies on lower-temperature boilers report a predominance of sulfates, this result implies that the toxicity of HFO PM depends on its combustion conditions. Finally, we observed a 4-to-25-fold enhancement in the ratio V:Ni in soot particles versus PM2.5, indicating an enrichment of V in soot due to its lower nucleation/condensation temperature. As this enrichment mechanism is not dependent on soot formation, V is expected to be generally enriched within smaller HFO-PM particles from marine engines, enhancing its toxicity

Tracking the international spread of SARS-CoV-2 lineages B.1.1.7 and B.1.351/501Y-V2

Publisher Copyright: © 2021 O'Toole Á et al.Late in 2020, two genetically-distinct clusters of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) with mutations of biological concern were reported, one in the United Kingdom and one in South Africa. Using a combination of data from routine surveillance, genomic sequencing and international travel we track the international dispersal of lineages B.1.1.7 and B.1.351 (variant 501Y-V2). We account for potential biases in genomic surveillance efforts by including passenger volumes from location of where the lineage was first reported, London and South Africa respectively. Using the software tool grinch (global report investigating novel coronavirus haplotypes), we track the international spread of lineages of concern with automated daily reports, Further, we have built a custom tracking website (cov-lineages.org/global_report.html) which hosts this daily report and will continue to include novel SARS-CoV-2 lineages of concern as they are detected.Peer reviewe

A homogenized model for progressive delamination of laminated structures with cohesive interfaces loaded dynamically

none1Massabo' RMassabo', Robert

Modeling laminated composites with cohesive interfaces: a homogenization approach

A mechanical model is formulated for laminated shells with cohesive interfaces loaded dynamically. The model decomposes the shell into sub-shells joined by cohesive interfaces, which describe actual and potential fracture surfaces. A homogenization technique is applied to reduce the number of unknowns of the problem and make it independent of the numbers of sub-shells used to discretize the system. The accuracy of the approach in the presence of highly imperfect interfaces and delaminations is verified using an exact elasticity solution based on an extension of Pagano\u2019s (1969) model for multilayered plates with perfect interfaces

Characterizing bridged cracks in fibrous high-strength concrete

An inverse problem based on a bridged-crack model is formulated to characterize the toughening mechanisms in fibrous high-strength concretes. Experimental data of short three-point bend specimens are used in the analysis

An efficient model for laminated beams with cohesive interfaces

A mechanical model formulated by the authors to study laminated shells with cohesive interfaces loaded dynamically is particularized here to plates deforming in cylindrical bending under quasi-static loading. The plate is modeled as an assembly of sub-layers joined by cohesive interfaces, which define actual and potential fracture surfaces. A homogenized displacement field is derived by imposing a-priori continuity conditions between sub-layers, thus reducing the number of unknowns of the problem and making it independent of the number of layers. The accuracy of the model is verified through a comparison with an exact elasticity solution