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Results on direct radiative forcing of aerosols obtained over the tropical Indian Ocean

CURRENT SCIENCE 1999年第7期76卷 924-930页

作者： Jayaraman, A Phys Res Lab Ahmedabad 380009 Gujarat India

aerosols reduce the surface reaching solar flux (negative radiative forcing) by scattering the incoming solar radiation out to space. Various model studies on climate change suggest that surface cooling induced by aerosol scattering is the largest source of uncertainty in predicting the future climate. Measurements made by ORV Sagar Kanya over the tropical Indian Ocean, as part of the pre-INDOEX campaign, in January to March of 1996, 1997 and 1998 consistently present aerosol characteristics with large spatial and temporal variations. The columnar aerosol optical depths measured at different spectral bands using a sun-photometer reveal a systematic latitude gradient in aerosol amount decreasing from north to south, until the Inter-Tropical Convergence Zone (ITCZ), Independent surface level aerosol size distribution measurement complement the optical depth data. The submicron size particles of radius less than 0.5 mu m are responsible for the high aerosol optical depths obtained north of the ITCZ. Surface reaching direct solar and global (solar plus sky) radiation intensities are measured using standard pyrheliometers, pyranometers and photodiode radiometers. Data on aerosol optical depth and radiation intensities available simultaneously on cloud-free days are correlated to estimate the direct radiative forcing by aerosols, Combining the 1996 and 1997 cruise data, the diurnal averaged radiative forcing for the tropical Indian Ocean is obtained as - 5.2 W m(-2), which is the reduction in the global flux for every 0.1 increase in aerosol optical depth. This is the first ever direct experimental evidence on the aerosol radiative forcing which applies to the aerosols found over the tropical Indian Ocean during January to March. This value is higher than the computed global average value, which is about -2 W m(-2). The excess forcing could only be explained by an excess absorption by aerosols or by other atmospheric constituents which are hitherto unaccounted for in the

关键词： aerosols Optical thickness Radiative forcing Cruises Oceans Particle mass Wavelengths Zenith Coasts Research and development laboratories

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ON THE FILTRATION OF FIBROUS aerosols

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SCIENCE OF THE TOTAL ENVIRONMENT 1986年第3期52卷 189-199页

作者： SPURNY, KR Fraunhofer-Institute for Environmental Chemistry and Ecotoxicology 5948 Schmallenberg-Grafschaft Federal Republic of Germany

Basic processes occurring during the filtration of fibrous aerosols are discussed. Using aerosols containing very fine asbestos fibers, the filtration efficiencies of some analytical ***, Millipore and fiber *** investigated. The collection efficiences were determined by electron microscopy and radiolabeled asbestos fibers and were found to depend upon the pore size of the filter and on the form of the fiber of the respective aerosols. The collection efficiencies were found to lie in the range 40-99.9%. A special problem discussed concerns the orientation of fibrous particles in the vicinity of the entrances to pores in the filter.

关键词： aerosols

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Influence of source distribution and geochemical composition of aerosols on children exposure in the large polymetallic mining region of the Bolivian Altiplano

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SCIENCE OF THE TOTAL ENVIRONMENT 2011年 412卷 170-184页

作者： Goix, Sylvaine Point, David Oliva, Priscia Polve, Mireille Duprey, Jean Louis Mazurek, Hubert Guislain, Ludivine Huayta, Carlos Barbieri, Flavia L. Gardon, Jacques Univ Toulouse IRD CNRS GET F-31400 Toulouse France IRD LCA UMSA La Paz Bolivia Univ Aix Marseille 1 IRD UMR151 Lab Populat Environm Dev F-13331 Marseille 3 France IRD La Paz Bolivia IRD Hydrosci Montpellier France

The Bolivian Altiplano (Highlands) region is subject to intense mining, tailing and smelting activities since centuries because of the presence of large and unique polymetallic ore deposits (Ag, Au, Cu, Pb, Sn, Sb, Zn). A large scale PM10, Pm-2.5 aerosol monitoring survey was conducted during the dry season in one of the largest mining cities of this region (Oruro, 200,000 inhabitants). Aerosol fractions, source distribution and transport were investigated for 23 elements at approximately 1 km(2) scale resolution, and compared to children exposure data obtained within the same geographical space. As, Cd, Pb, Sb, W and Zn in aerosols are present at relatively high concentrations when compared to studies from other mining regions. Arsenic exceeds the European council PM10 guide value (6 ng/m(3)) for 90% of the samples, topping 200 ng/m(3). Ag, As, Cd, Cu, Pb and Sb are present at significantly higher levels in the district located in the vicinity of the smelter zone. At the city level, principal component analysis combined with the mapping of factor scores allowed the identification and deconvolution of four individual sources: i) a natural magmatic source (Co, Cs, Fe, K. Mn, Na, Rb and U) originating from soil dust, resuspended by the traffic activity;ii) a natural sedimentary source (Mg, Ca, Sr, Ba and Th) resulting from the suspension of evaporative salt deposits located South;iii) an anthropogenic source specifically enriched in mined elements (As, Cd, Cu, Pb, Sb and Zn) mainly in the smelting district of the city;and iv) a Ni-Cr source homogenously distributed between the different city districts. Enrichment factors for As, Cd and Sb clearly show the impact of smelting activities, particularly in the finest PM2.5 fraction. Comparison to children's hair metal contents collected in five schools from different districts shows a direct exposure to smelting activity fingerprinted by a unique trace elements pattern (Ag, As, Cu, Pb, Sb). (C) 2011 Elsevier B.V. All right

关键词： aerosols Smelting activities Mining activities Heavy metals Human health Enrichment factors

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Modelling the size-dependent collection efficiency of hedgerows for ambient aerosols

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JOURNAL OF AEROSOL SCIENCE 2006年第8期37卷 990-1015页

作者： Tiwary, Abhishek Morvan, Herve P. Colls, Jeremy J. Univ Nottingham Sch Biosci Nottingham NG7 2RD England Univ Nottingham Sch Civil Engn Nottingham NG7 2RD England

A model for estimating the size-segregated particle collection efficiencies of three hedgerow species of different aerodynamic porosities has been developed and tested in the particle size range 0.5-20 mu m. Collection efficiency (CE) has been described in terms of the coupled effects of the deviation of the approach flow (CEflow) and the filtration through the foliage elements (CEfiltration). Variations in barrier porosities with wind speed, which govern both the flow and the particle collection mechanism, have been modelled using an empirical parameter called the "rigidity factor" (r) for representative leaf-sizes of the three hedge types. Computational fluid dynamics (CFD) allows simulation of velocity fields and turbulence around the barriers, leading to identification of prominent flow separation zones in the wake of denser hedges. Application of different turbulence closure schemes in the CFD model influences the predicted CE only for particles above (5 mu m). Field validations obtained for a porous (hawthorn) and a denser (yew) hedge indicate that CEfiltration ranges between 10 and 35% for "coarse" particles (10-20 mu m) and 1-5% for "fine" particles (0.5-3.5 mu m), the porous hedge showing higher values in the former case and vice versa in the latter. Model predictions of CE over the particle size range studied for the porous hedge lie within 1-30% and for the denser hedge within 0.4-3%. (C) 2005 Elsevier Ltd. All rights reserved.

关键词： hedgerows resistance coefficient collection efficiency aerosols CFD

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Accurate Representations of the Microphysical Processes Occurring during the Transport of Exhaled aerosols and Droplets

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ACS CENTRAL SCIENCE 2021年第1期7卷 200-209页

作者： Walker, Jim S. Archer, Justice Gregson, Florence K. A. Michel, Sarah E. S. Bzdek, Bryan R. Reid, Jonathan P. Univ Bristol Sch Chem Bristol BS8 1TS Avon England

aerosols and droplets from expiratory events play an integral role in transmitting pathogens such as SARS-CoV-2 from an infected individual to a susceptible host. However, there remain significant uncertainties in our understanding of the aerosol droplet microphysics occurring during drying and sedimentation and the effect on the sedimentation outcomes. Here, we apply a new treatment for the microphysical behavior of respiratory fluid droplets to a droplet evaporation/sedimentation model and assess the impact on sedimentation distance, time scale, and particle phase. Above a 100 mu m initial diameter, the sedimentation outcome for a respiratory droplet is insensitive to composition and ambient conditions. Below 100 mu m, and particularly below 80 mu m, the increased settling time allows the exact nature of the evaporation process to play a significant role in influencing the sedimentation outcome. For this size range, an incorrect treatment of the droplet composition, or imprecise use of RH or temperature, can lead to large discrepancies in sedimentation distance (with representative values >1 m, >2 m, and >2 m, respectively). Additionally, a respiratory droplet is likely to undergo a phase change prior to sedimenting if initially <100 mu m in diameter, provided that the RH is below the measured phase change RH. Calculations of the potential exposure versus distance from the infected source show that the volume fraction of the initial respiratory droplet distribution, in this size range, which remains elevated above 1 m decreases from 1 at 1 m to 0.125 at 2 m.

关键词： Anatomy Liquids Sedimentation aerosols Fluids

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Effect of aerosols on Freezing Drops, Hail, and Precipitation in a Midlatitude Storm

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JOURNAL OF THE ATMOSPHERIC SCIENCES 2016年第1期73卷 109-144页

作者： Ilotoviz, Eyal Khain, Alexander P. Benmoshe, Nir Phillips, Vaughan T. J. Ryzhkov, Alexander V. Hebrew Univ Jerusalem Dept Atmospher Sci IL-91904 Jerusalem Israel NOAA Geophys Fluid Dynam Lab Princeton NJ USA Lund Univ Dept Phys Geog & Ecosyst Sci Lund Sweden Univ Oklahoma Cooperat Inst Mesoscale Meteorol Studies Norman OK 73019 USA

A midlatitude hail storm was simulated using a new version of the spectral bin microphysics Hebrew University Cloud Model (HUCM) with a detailed description of time-dependent melting and freezing. In addition to size distributions of drops, plate-, columnar-, and branch-type ice crystals, snow, graupel, and hail, new distributions for freezing drops as well as for liquid water mass within precipitating ice particles were implemented to describe time-dependent freezing and wet growth of hail, graupel, and freezing *** carried out using different aerosol loadings show that an increase in aerosol loading leads to a decrease in the total mass of hail but also to a substantial increase in the maximum size of hailstones. Cumulative rain strongly increases with an increase in aerosol concentration from 100 to about 1000 cm(-3). At higher cloud condensation nuclei (CCN) concentrations, the sensitivity of hailstones' size and surface precipitation to aerosols decreases. The physical mechanism of these effects was analyzed. It was shown that the change in aerosol concentration leads to a change in the major mechanisms of hail formation and growth. The main effect of the increase in the aerosol concentration is the increase in the supercooled cloud water content. Accordingly, at high aerosol concentration, the hail grows largely by accretion of cloud droplets in the course of recycling in the cloud updraft zone. The main mechanism of hail formation in the case of low aerosol concentration is freezing of raindrops.

关键词： Studies Meteorology aerosols Clouds Hail Storms

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Evaluating inter-continental transport of fine aerosols: (1) Methodology, global aerosol distribution and optical depth

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ATMOSPHERIC ENVIRONMENT 2009年第28期43卷 4327-4338页

作者： Liu, Junfeng Mauzerall, Denise L. Horowitz, Larry W. Ginoux, Paul Fiore, Arlene M. Princeton Univ GFDL NOAA Princeton NJ 08540 USA Princeton Univ Woodrow Wilson Sch Princeton NJ 08544 USA

Our objectives are to evaluate inter-continental source-receptor relationships for fine aerosols and to identify the regions whose emissions have dominant influence on receptor continents. We simulate sulfate, black carbon (BC), organic carbon (OC), and mineral dust aerosols using a global coupled chemistry-aerosol model (MOZART-2) driven with NCEP/NCAR reanalysis meteorology for 1997-2003 and emissions approximately representing year 2000. The concentrations of simulated aerosol species in general agree within a factor of 2 with observations, except that the model tends to overestimate sulfate over Europe in summer, underestimate BC and OC over the western and southeastern (SE) U.S. and Europe, and underestimate dust over the SE U.S. By tagging emissions from ten continental regions, we quantify the contribution of each region's emissions on surface aerosol concentrations (relevant for air quality) and aerosol optical depth (AOD, relevant for visibility and climate) globally. We find that domestic emissions contribute substantially to surface aerosol concentrations (57-95%) over all regions, but are responsible for a smaller fraction of AOD (26-76%). We define "background" aerosols as those aerosols over a region that result from inter-continental transport, DMS oxidation, and emissions from ships or volcanoes. Transport from other continental source regions accounts for a substantial portion of background aerosol concentrations: 36-97% for surface concentrations and 38-89% for ACID. We identify the Region of Primary Influence (RPI) as the source region with the largest contribution to the receptor's background aerosol concentrations (or AOD). We find that for dust Africa is the RPI for both aerosol concentrations and AOD over all other receptor regions. For non-dust aerosols (particularly for sulfate and BC), the RPIs for aerosol concentrations and AOD are identical for most receptor regions. These findings indicate that the reduction of the emission of non-dust a

关键词： Inter-continental transport Source-receptor relationships aerosols Air quality Optical depth

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Geochemical Behaviour of the Tunisian Background aerosols in Sirocco Wind Circulations

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Advances in Atmospheric Sciences 2009年第3期26卷 390-402页

作者： Chafai AZRI Habib ABIDA Khaled MEDHIOUB Department of Geology Faculty of Sciences of Sfax (FSS)BP 11713000 SfaxTunisia Institute of Preparatory Engineering Studies of Sfax (IPEIS) BP 8053018 SfaxTunisia

This study examines spatial and time evolutions of the principal constituents of the Tunisian background aerosols under Sirocco wind circulations. aerosols coming from the Sahara Desert were found to be loaded with particulate matter, especially silicon. The aerosols were shown to have varying geochemical behaviour along the ＂South-North＂ displacement of the Saharan plumes, depending on the wind flow characteristics, geomorphologic features and the nature of soils swept by the wind. In the south and the center part of the country, the transfer of aerosol constituents to the soil （by gravity and/or impaction） was probably predom- inated by localized enrichment phenomena. The latter are reinforced by the effect of turbulent winds over bare soils, wind wakes and probably selective disintegration, especially in the vicinity of the geomorphologic features of central Tunisia. These relatively high features, extending over important distances, appear to be of paramount importance for the phenomena of redistribution of aerosol constituents even during periods without Sirocco wind circulations. In the northern section of the country, aerosol constituent concentrations dropped to almost 50%, in spite of the abundance of localized turbulent winds. This may be explained by the effect of forests and the relatively dense vegetation cover, which clearly reinforces the transfer phenomena to the soil and the attenuate of dust entrainment.

关键词： aerosols Sahara Sirocco Tunisia turbulent winds

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Bacterial Communities in Marine aerosols Revealed by 454 Pyrosequencing of the 16S rRNA Gene

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JOURNAL OF THE ATMOSPHERIC SCIENCES 2015年第8期72卷 2997-3008页

作者： Xia, Xiaomin Wang, Jianjun Ji, Jiabin Zhang, Jiexia Chen, Liqi Zhang, Rui Hong Kong Univ Sci & Technol Div Environm Sci Kowloon Hong Kong Peoples R China State Ocean Adm Inst Oceanog 3 Key Lab Global Change & Marine Atmospher Chem Xiamen 361005 Fujian Peoples R China Xiamen Univ Inst Marine Microbes & Ecospheres State Key Lab Marine Environm Sci Xiamen Fujian Peoples R China

Although bacteria are an important biological component of aerosol particles, studies of bacterial communities in remote marine aerosol are largely lacking. In this study, aerosol samples were collected over the western Pacific Ocean, the northern Pacific Ocean, the Arctic Ocean, and the Norwegian Sea during the Fifth Chinese National Arctic Research Expedition (CHINARE 5). The diversity and structure of aerosol bacterial communities, based on 454 pyrosequencing, were explored in these samples. The bacterial community in the aerosols collected over the Pacific Ocean was more diverse than over the Norwegian Sea. Both temporal and spatial variations in aerosol bacterial communities were observed based on phylogenetic analysis. These results suggest that the source of air masses shape bacterial communities in aerosol particles over remote marine regions. aerosols are clearly important for long-range transport of bacteria. Since potential human pathogens (e.g., Streptococcus sp.) were retrieved in this study, further investigation is needed to evaluate the potential for their long-distance migration via aerosol.

关键词： Spatial variations Community composition aerosols Genes Atmospheric sciences Pathogens Phylogenetics Expeditions Phylogeny spatial variations Oceans rRNA 16S Migration Air masses Long-range transport Aerosol particles Marine aerosols Arctic Ocean Arctic research Streptococcus Shape Bacteria Air Masses Arctic

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Laboratory polarization nephelometer for measurements of optical properties of aerosols

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MEASUREMENT SCIENCE AND TECHNOLOGY 2007年第3期18卷 632-638页

作者： Daugeron, D. Renard, J-B Personne, P. Brun, G. Andre, J-M Univ Blaise Pascal Lab Meteorol Phys Clermont Ferrand France Lab Phys & Chim Environm Orleans France Univ St Etienne Lab Traitement Signal & Instrumentat St Etienne France

Polarization measurements are a powerful tool for better documentation of a variety of liquid and solid particles found in the Earth's atmosphere. Because the solid particles have a non-symmetrical shape, which thereby prevents modelling calculations, it is necessary to build a database of the scattering properties of irregular solid particles in order to interpret the results of remote sensing measurements from aircraft, balloon and satellite. A new laboratory polarization nephelometer was built for this purpose. The particles are levitated by continuous airflow, and are illuminated by a laser at a wavelength of 802 nm. Two avalanche photodiode sensors are used for recording the components of the scattered light perpendicular and parallel to the scattering plane. Detector amplifiers allow light-power detection from a few microwatts down to a few picowatts. Measurements with liquid droplets, made for scattering angles in the 20 degrees-160 degrees range, are in agreement with theoretical calculations, showing that the instrument works well. The first results obtained for irregular solid particles are also presented.

关键词： polarization aerosols dust atmosphere

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