Search results for "Mixture"

Electron microscopy of particles collected at Praia, Cape Verde, during the Saharan Mineral Dust Experiment: particle chemistry, shape, mixing state …

2011

A large field experiment of the Saharan Mineral Dust Experiment (SAMUM) was performed in Praia, Cape Verde, in January and February 2008. The aerosol at Praia is a superposition of mineral dust, sea-salt, sulphates and soot. Particles smaller than 500 nm are mainly mineral dust, mineral dust–sulphate mixtures, sulphates and soot–sulphate mixtures. Particles larger then 2.5 μm consist of mineral dust, sea-salt and few mineral dust–sulphate mixtures. A transition range exists in between. The major internal mixtures are mineral dust–sulphate and soot–sulphate. Mineral dust–sea-salt mixtures occur occasionally, mineral dust–soot mixtures were not observed. The aspect ratio was 1.3–1.4 for dry p…

Aerosol influences on low-level clouds in the West African monsoon

2019

Abstract. Low-level clouds (LLC) cover a wide area of southern West Africa (SWA) during the summer monsoon months, and have an important cooling effect on the regional climate. Previous studies of these clouds have focused on modelling and remote sensing via satellite. We present the first comprehensive set of regional, in situ measurements of cloud microphysics, taken during June – July 2016, as part of the DACCIWA (Dynamics-Aerosol-Chemistry-Clouds Interactions in West Africa) campaign, assessing spatial and temporal variation in the properties of these clouds. LLC developed overnight and mean cloud cover peaked a few hundred kilometres inland around 10:00 local solar time (LST), before c…

Assessments for the impact of mineral dust on the meningitis incidence in West Africa.

2013

9 pages; International audience; Recently, mineral dust has been suspected to be one of the important environmental risk factor for meningitis epidemics in West Africa. The current study is one of the first which relies on long-term robust aerosol measurements in the Sahel region to investigate the possible impact of mineral dust on meningitis cases (incidence). Sunphotometer measurements, which allow to derive aerosol and humidity parameters, i.e., aerosol optical thickness, Angström coefficient, and precipitable water, are combined with quantitative epidemiological data in Niger and Mali over the 2004-2009 AMMA (African Monsoon Multidisciplinary Analysis) program period. We analyse how th…

A Laboratory Dust Generator Applying Vibration to Soil Sample: Mineralogical Study and Compositional Analyses

2020

International audience; A laboratory study was carried out using a vibrating system (SyGAVib) to produce aerosols from four soils collected in the central Tunisian region around Sfax. The aim of this device is to mimic dust emission by natural wind erosion. Using compositional analysis, the dust produced was compared to (i) dust generated in a wind tunnel by the same soils, (ii) fine sieved and (iii) original bulk soils, and (iv) naturally occurring aerosol samples collected in the same area. The relative quartz content strongly decreases from bulk to fine soils, and again from fine soils to both wind tunnel and vibration‐generated aerosols. Compositional data analysis (CoDA) clearly shows …

Clouds and aerosols in Puerto Rico - a new evaluation

2007

The influence of aerosols, both natural and anthropogenic, remains a major area of uncertainty when predicting the properties and behaviour of clouds and their influence on climate. In an attempt to better understand warm cloud formation in a tropical marine environment, a period of intensive measurements took place in December 2004 in Puerto Rico, using some of the latest developments in online instrumentation such as aerosol mass spectrometers, cloud condensation nuclei counters and a hygroscopicity tandem differential mobility analyser. Simultaneous online measurements of aerosol size distributions, composition, hygroscopicity and optical properties were made near the lighthouse of Cape …

Outdoor, indoor and personal distribution of BTEX in pregnant women from two areas in Spain - Preliminary results from the INMA project

2010

Volatile organic compounds (VOCs), which are habitually found in both outdoor and indoor environments, may represent a significant health risk. In this context, pregnancy is a critical period since foetuses are more vulnerable than adults to exposure to toxic compounds. The objective of this study is to present the preliminary results of a series of measurements of outdoor (O), indoor (I) and personal exposure (P) to benzene, toluene, ethylbenzene, o-xylene and m,p-xylene (BTEX) in 107 pregnant women from two areas in Spain, namely Valencia and Sabadell. BTEX samplers were installed for 48 hours both inside and outside of the women’s homes, along with personal samplers. In addition, the tes…

State of mixing, shape factor, number size distribution, and hygroscopic growth of the Saharan anthropogenic and mineral dust aerosol at Tinfou, Moro…

2009

The Saharan Mineral Dust Experiment (SAMUM) was conducted in May and June 2006 in Tinfou, Morocco. A H-TDMA system and a H-DMA-APS system were used to obtain hygroscopic properties of mineral dust particles at 85% RH. Dynamic shape factors of 1.11, 1.19 and 1.25 were determined for the volume equivalent diameters 720, 840 and 960 nm, respectively. During a dust event, the hydrophobic number fraction of 250 and 350 nm particles increased significantly from 30 and 65% to 53 and 75%, respectively, indicating that mineral dust particles can be as small as 200 nm in diameter. Log-normal functions for mineral dust number size distributions were obtained from total particle number size distributio…

2011

Abstract. The ability of coated mineral dust particles to act as ice nuclei (IN) was investigated at LACIS (Leipzig Aerosol Cloud Interaction Simulator) during the FROST1- and FROST2-campaigns (Freezing of dust). Sulphuric acid was condensed on the particles which afterwards were optionally humidified, treated with ammonia vapour and/or heat. By means of aerosol mass spectrometry we found evidence that processing of mineral dust particles with sulphuric acid leads to surface modifications of the particles. These surface modifications are most likely responsible for the observed reduction of the IN activation of the particles. The observed particle mass spectra suggest that different treatme…

A numerical model of the cloud-topped planetary boundary-layer: chemistry in marine stratus and the effects on aerosol particles

1999

Abstract In a numerical study the effect of stratiform clouds on aerosol particles is investigated. This is done with the one-dimensional chemical microphysical stratus model CHEMISTRA. In the microphysical part of the model special emphasis is layed on a detailed description of cloud microphysical processes by means of a joint two-dimensional particle distribution for aerosols and cloud droplets. In the chemical part of the model the particle spectrum is subdivided into three categories referring to unactivated aerosols, small and large cloud droplets. Aqueous-phase chemical reactions are separately treated in the two droplet size classes. Numerical results show that within the boundary-la…

The transatlantic dust transport from North Africa to the Americas-Its characteristics and source regions

2015

Transport of Saharan dust over the Atlantic to the Americas is a relevant process since dust is a nutrient for marine and terrestrial ecosystems. It is therefore important to better quantify the frequency and amount of transatlantic dust transport, its preferred altitude and duration, and the regions of dust origin. This study uses a novel combination of Eulerian and Lagrangian diagnostics, applied to a previously validated 5 year simulation of the fifth generation European Centre for Medium Range Weather Forecast-Hamburg-model (ECHAM5)/Modular Earth Submodel System (MEESy) Atmospheric Chemistry model, to quantify these dust transport characteristics and their seasonal variations. Results c…