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

PM10 source apportionment based on PMF and chemical tracers during different cruises in Western Mediterranean

In the Western Mediterranean Basin, frequently exposed to high levels of air pollutants, an important source of pollution which influence the emission, is the intensive ship traffic. The Joint Research Centre of the European Commission (JRC, EC) has started a long-term monitoring program along different years over the Mediterranean Sea based on observations from a cruise ship following a regular route in the Western Mediterranean, in collaboration with the Department of Physics of University of Genoa. In this framework, an intensive PM10 sampling campaign was organized in the summer of 2011, in order to fill in the gap of data recovered (in term of PM speciation) during the previous campaigns (Schembari et al., 2014) and to get a better and complete description of PM sources. During this campaign the route of the ship was Civitavecchia-Savona-Barcelona-Palma de Mallorca- Malta (Valletta)-Palermo-Civitavecchia (see Figure 1). The PM samples were collected on Quartz and Teflon filters (47mm diameter, flow rate 2.3 m3/h) using in parallel two Sven Leckel Ingenieurburo sequential samplers, placed on the top of the cabin where the monitoring and meteorological station was located. Samples were analyzed with different techniques: Energy Dispersive X-Ray Fluorescence at the Department of Physics of Genoa (Ariola et al, 2006); Ion Chromatography (Chow and Watson, 1999) at Department of Chemistry of University of Milan; Thermo-optical analysis (Birch and Cary, 1996) at the JRC laboratory. Ion Beam Analysis measurements of the Teflon filters sampled during the week of September 2011, using simultaneously PIXE, EBS and PESA techniques (Chiari, 2005), were performed at the 3 MV Tandetron accelerator of the LABEC laboratory of INFN in Florence. The data were used to identify and characterize the main PM10 sources along the ship route, with a focus on ship emissions, through apportionment Positive Matrix Factorization receptor modelling, PMF (Paatero et al, 1994). Particular attention was given to the evidence of emissions from heavy fuel oil combustion by ships, known to be an important source of secondary sulphate aerosol. Five sources of aerosol were resolved by the PMF analysis with a new database. The analysis allows distinguishing between secondary and primary particle mass resulting from ship emissions: V and Ni were found to be suitable tracers of heavy fuel oil combustion source during the campaign. The source having the largest impact on PM10 was identified as Sulphate source by PMF. The correlations between Sulphate and V and Ni showed the influence of ship emissions on sulphate in marine air masses

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)

ChAMBRe: studi su bio-aerosol in camera di simulazione atmosferica

Nella Sezione di Genova dell\u2019Istituto Nazionale di Fisica Nucleare \ue8 stata recentemente installata, in collaborazione con il Laboratorio di Fisica Ambientale del Dipartimento di Fisica dell\u2019Universit\ue0 di Genova, ChAMBRe (Chamber for Aerosol Modelling and Bio-aerosol Research), la prima Camera di simulazione atmosferica specificatamente concepita per studiare la componente biologica dell\u2019aerosol atmosferico. Presso la camera di simulazione atmosferica CESAM (Cr\ue9teil, Francia) sono sati effettuati alcuni esperimenti pilota recentemente pubblicati [1], che sono stati lo spunto per la costruzione di una struttura dedicata allo studio del comportamento dei pi\uf9 comuni agenti patogeni presenti in atmosfera sotto forma di bioaerosol e in particolare dei meccanismi che controllano le interazioni tra questi e le altre componenti dell\u2019aerosol e pi\uf9 in generale dell\u2019atmosfera. L\u2019attivit\ue0 di ricerca a ChAMBRe si concentrer\ue0 sull\u2019indagine del comportamento del bio-aerosol in differenti condizioni atmosferiche e in presenza di tipici inquinanti antropici (come il monossido di carbonio, gli ossidi di azoto, etc.) che possono influenzare la vitalit\ue0, la morfologia e la dispersione dei batteri in atmosfera. Come primo passo \ue8 necessario innanzitutto mettere a punto un protocollo che garantisca la riproducibilit\ue0 degli esperimenti in una struttura complessa come ChAMBRe. Ci si \ue8 quindi concentrati su aspetti cruciali quali: crescita in vitro e successiva iniezione in camera di una data concentrazione di batteri, seguita da una fase di estrazione, campionamento e misura della vita media all\u2019interno della camera. Gli esperimenti sono volti anche ad identificare eventuali condizioni di stress ambientali e meccaniche per i microrganismi e la loro risposta come singoli individui e come colonie. Sono stati eseguiti esperimenti su due tipologie di ceppi batterici frequentemente utilizzati come organismi modello: il Bacillus subtilis e l\u2019Escherichia coli, appartenenti rispettivamente al gruppo dei Gram-positivi e dei Gram-negativi. I risultati e il protocollo sperimentale messo a punto verranno presentati a PM2018

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

Un sistema ottico automatico per la determinazione del contenuto di Black Carbon in filtri standard per la raccolta del particolato atmosferico

A partire dai risultati di studi preliminari [1] abbiamo progettato e costruito un nuovo sistema motorizzato, gestito in piattaforma Labview 8.5, che consente la determinazione del contenuto di Black Carbon su filtri standard da 47 mm. Lo strumento \ue8 basato su un laser 635 nm e su alcuni fotodiodi che misurano la luce trasmessa ad angoli differenti. Il sistema, completamente automatizzato, \ue8 composto da una ruota, in grado di alloggiare fino a 16 filtri, e da tre motori passo-passo che consentono la scansione della superficie dei filtri. Presentiamo i risultati della messa a punto e caratterizzazione del sistema, inclusa la calibrazione effettuata per confronto con altri strumenti ottici e termo-ottici, e i primi risultati ottenuti su campioni di PM10, PM2.5 raccolti in aree urbane e marine. Discutiamo anche i possibili sviluppi futuri per l\u2019analisi di campioni disomogenei quali quelli prodotti da impattori inerziali a cascata

Tailored coefficients in the algorithm to assess reconstructed light extinction at urban sites: A comparison with the IMPROVE revised approach

Estimates of light extinction and visibility are routinely performed by the U.S. Interagency Monitoring of Protected Visual Environments (IMPROVE) network using a simple algorithm which assesses light extinction coefficient (bext) at remote and rural sites from concentrations of major particulate matter (PM) species, NO2,and Rayleigh scattering from clear-air gaseous components. Following the same approach, in this paper an equation with tailored (i.e. site-specific) coefficients was implemented with the aim of reducing uncertainties and assumptions of the IMPROVE algorithm for applications at polluted urban sites. Major differences compared to IMPROVE algorithm are: 1) dry mass extinction efficiencies calculated using a discrete dipole approximation code with aerosol size distributions measured at our monitoring site as input data; 2) site-specific water growth functions computed separately for ammonium sulfate, ammonium nitrate, and organic matter; 3) fine soil evaluated using an equation previously adopted at our urban site; 4) aerosol absorption component assessed directly through filter-based optical measurements. Details about the calculations performed are reported in the paper and the comparison with the IMPROVE revised algorithm is discussed. The tailored approach here proposed to estimate reconstructed light extinction was applied to PM2.5 test samples collected on purpose in Milan (Italy), where heavy pollution episodes occur during winter periods. In addition, visual range was calculated applying the Koschmieder equation and compared to visibility measured at the nearby Milano-Linate airport obtaining a fairly good correlation