Search results for "Particle-size distribution"

2009

Abstract. We have investigated the formation of cloud droplets under pyro-convective conditions using a cloud parcel model with detailed spectral microphysics and with the κ-Kohler model approach for efficient and realistic description of the cloud condensation nucleus (CCN) activity of aerosol particles. Assuming a typical biomass burning aerosol size distribution (accumulation mode centred at 120 nm), we have calculated initial cloud droplet number concentrations (NCD) for a wide range of updraft velocities (w=0.25–20 m s−1) and aerosol particle number concentrations (NCN=200–105 cm−3) at the cloud base. Depending on the ratio between updraft velocity and particle number concentration (w/…

Application Of Microholography for Ground-based In Situ Measurements in Stratus Cloud Layers: A Case Study

1993

Abstract A holographic droplet and aerosol recording system (HODAR) has been designed and operated in situ in a low-level stratus cloud layer adopting the Fraunhofer in-line technique to measure sizes and velocity vectors of cloud droplets as well as to determine sizes and shapes of other hydrometeors (e.g., graupel). The particle-size radii covered by this ground-based instrument range from three to several hundred micrometers. A case study conducted on the Kleiner Feldberg Mountain Observatory near Frankfurt, Germany, during November 1990 documents the temporal evolution of the cloud-droplet size distribution over a period of 19 h during which the size distribution changed from monomodal …

Composition and mixing state of the urban background aerosol in the Rhein-Main area (Germany)

2007

Abstract Size-resolved aerosol particle samples in the size range 0.1–10 μm aerodynamic diameter were collected in the years 2003 and 2004 at an urban background station in Mainz, Germany. Size, morphology, chemical composition and mixing state of more than 5400 individual particles of 7 selected sampling days were analyzed in detail by scanning electron microscopy and energy-dispersive X-ray microanalysis. In addition, transmission electron microscopy, aerosol mass spectrometry and atomic force microscopy were applied to obtain detailed information about the mixing state of the particles. The fine particle fraction (diameter 1 μm diameter) is strongly dependant on air mass history with var…

Sources, size distribution, and downwind grounding of aerosols from Mount Etna

2006

The number concentrations and size distributions of aerosol particles >0.3 mm diameter were measured at the summit of Mount Etna and up to 10 km downwind from the degassing vents during July and August 2004. Aerosol number concentrations reached in excess of 9 106 L1 at summit vents, compared to 4–8 104 L1 in background air. Number concentrations of intermediate size particles were higher in emissions from the Northeast crater compared to other summit crater vents, and chemical composition measurements showed that Northeast crater aerosols contained a higher mineral cation content compared to those from Voragine or Bocca Nuova, attributed to Strombolian or gas puffing activity within the ve…

Competition of coagulation sink and source rate: New particle formation in the Pearl River Delta of China

2010

The coagulation sink and its role in new particle formation are investigated based on data obtained during the PRIDE-PRD2004 campaign at Xinken of Pearl River Delta, China. Analysis of size distributions and mode contributions of the coagulation sink show that the observed higher load of accumulation mode particles impose a significant effect on the coagulation sink and result in higher coagulation sinks at Xinken despite of the lower total particle number compared with other areas. Hence it is concluded that the higher coagulation sink may depress the occurrence frequency of new particle formation events. The strategies targeting at controlling accumulation mode particles may have influenc…

Size distribution, mass concentration, chemical and mineralogical composition and derived optical parameters of the boundary layer aerosol at Tinfou,…

2009

During the SAMUM 2006 field campaign in southern Morocco, physical and chemical properties of desert aerosols were measured. Mass concentrations ranging from 30 Ã�¼g m-3 for PM2.5 under desert background conditions up to 300,000 Ã�¼g m-3 for total suspended particles (TSP) during moderate dust storms were measured. TSP dust concentrations are correlated with the local wind speed, whereas PM10 and PM2.5 concentrations are determined by advection from distant sources. Size distributions were measured for particles between 20 nm and 500 Ã�¼m diameter (parameterizations are given). Two major regimes of the size spectrum can be distinguished. Smaller than 500 nm particle diameter, the distrib…

The ATAL within the 2017 Asian Monsoon Anticyclone: Microphysical aerosol properties derived from aircraft-borne in situ measurements

2021

The Asian summer monsoon is an effective pathway for aerosol particles and precursors from the planetary boundary layer over Central, South, and East Asia into the upper troposphere and lower stratosphere. An enhancement of aerosol particles within the Asian monsoon anticyclone (AMA), called the Asian tropopause aerosol layer (ATAL), has been observed by satellites. We discuss airborne in situ and remote sensing observations of aerosol microphysical properties conducted during the 2017 StratoClim field campaign within the AMA region. The aerosol particle measurements aboard the high-altitude research aircraft M55 Geophysica (maximum altitude reached of about 20.5 km) were conducted with a m…

Segmented Flow-Based Multistep Synthesis of Cadmium Selenide Quantum Dots with Narrow Particle Size Distribution

2015

A continuous-flow microreactor was used to synthetize II-VI semiconductor quantum dots (CdSe). In order to improve the size distribution of the nanoparticles, the synthesis was carried out in a two-step procedure. A seed solution was obtained in a separate nucleation step, followed by a controllable growth step. Quantum dots that are synthesized with the two-step method show a much narrower size distribution in comparison to those obtained in a conventional batch synthesis.

Electrokinetic Properties which Control the Coagulation of Silicate Cement Suspensions during Early Age Hydration

1998

The coagulation of cement particles during early age hydration has been previously identified as the first step of the setting and hardening of cement pastes. By hydrating Ca3SiO5and a silicate-rich clinker under controlled conditions, a correlation between the coagulation of the suspensions and the electrokinetic properties of particles is established. The zeta potential, and hence the surface charge, of particles in suspension depends on the calcium content of the medium. At low concentrations of Ca2+, the zeta potential of Ca3SiO5particles, calcium silicate hydrate (C–S–H), and clinker is negative (<−30 mV) and the suspensions are well dispersed. A strong coagulation occurs at intermedia…

Studies on mechanism and physico-chemical parameters at the origin of the cement setting II. Physico-chemical parameters determining the coagulation …

1996

The physico-chemical parameters determining the coagulation of cements grains previously identified as the first fundamental process of cement setting have been investigated in diluted suspensions using an adapted granulometric method. The analysis of the influence of the ionic concentration in solution on the coagulation reveals that calcium concentration is the parameter which determines the particle interactions. There exists a minimum critical concentration of calcium ions in solution which is required to occur the coagulation of cement particles and a dispersive effect appears for very high concentrations. The results are discussed in relation with DLVO theory and specific interactions.