Laser desorption/ionization characteristics of single ultrafine multicomponent aerosols have been investigated. The results confirm earlier findings that (a) the negative ion spectra are dominated by free electrons an...
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Laser desorption/ionization characteristics of single ultrafine multicomponent aerosols have been investigated. The results confirm earlier findings that (a) the negative ion spectra are dominated by free electrons and (b)the ion yield-to-mass ratio is higher for ultrafine particles than th at of larger ones. The smallest relative mass of KCI detected in NaCl is about 0.06%, which corresponds to 10(-20) g of KCI in a 50-nm particle. Experimental results from mixtures of KCl/NaCl and NaCl/NH4NO3 show that, by measuring the peak area ratio of certain ions in the spectrum, the total composition can be inferred. The experimental results also show that ion yields vary with composition even for ultrafine particles, making multicomponent analysis of complex particles difficult. A simple model is developed to quantify the relationship between ion yield and particle composition. Using this model, a relative ion yield of 4.9 is found for K+ from KCl over Na+ from NaCl, while 4.4 is found for Na+ from NaCl over NO+ from NH4NO3. It has been shown that analyzing particles composed of chemicals with common cations but different anions, such as NaCl/NaNO3 from positive ion spectra, is also possible. The ability of laser desorption/ionization to detect trace metals is studied. With relative mass of each element on the order of 1%, which corresponds to the absolute mass of the order of 10(-17) g in a 60-nm particle, strong peaks of Na+, Mg+, K+, Cr+, Fe+, Cu+, Zn+, Cd+, Cs+, La+, and Pb+ are observed in the spectrum. The smallest amount detectable for some easily ionizable elements, such as K and Cs, should be much lower than 1%. Although no ion yield is observed for pure (NH4)(2)SO4 particles, peaks of S+ and SO+ associated with (NH4)(2)SO4 are shown in spectrum from mixtures of (NH4)(2)SO4, NH4NO3, and several trace metals. The application of laser desorption/ionization to measuring atmospheric ultrafine aerosols is also discussed.
Deposition loss of aerosol particles in a stirred tank has been studied experimentally by observing the time-dependent changes in particle number concentration for various intensities of stirring. The stirred tank use...
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Deposition loss of aerosol particles in a stirred tank has been studied experimentally by observing the time-dependent changes in particle number concentration for various intensities of stirring. The stirred tank used in this study is a standard baffled tank with six-bladed turbin impeller or three-bladed propeller, and the aerosol particles used are monodisperse uncharged NaCl, DEHS (diethylhexyl sebacate), and polystyrene latex particles. The experimental results have shown the clear dependence of the deposition rate on particle size and turbulent intensity of stirring, and also shown that for a given intensity there exists the particle size at which the deposition rate constant becomes minimum. From the comparison of the experimental results with the representative theory of Crump and Seinfeld (J. Aerosol Sci. 12, 405, 1981), it has been found that the experimental deposition rates can be explained well by their theory where the eddy diffusivity near wall is assumed to be proportional to 2.7th power of the distance from the wall. And the equation for predicting the minimum deposition velocity under a given stirring speed has been derived.
This paper presents a balloon-type experiment for directional observations of the radiance and of the polarization ratio of the light reflected toward the space by the earth-atmosphere system. A first flight was condu...
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This paper presents a balloon-type experiment for directional observations of the radiance and of the polarization ratio of the light reflected toward the space by the earth-atmosphere system. A first flight was conducted on 5 July, 1985 over the Bay of Biscay (SW of France). The goal was to monitor the tropospheric aerosols by taking advantage of the black surface offered by the ocean at near infrared wavelengths. During the first part of the flight, remote sensing of the aerosols was disturbed by fair weather cumulus, but cloudless observations could be selected, which exhibit typical features of the sunglint and of scattering by aerosols. The inversion of these measurements allows a characterization of the optical properties of the aerosols. During the second part of the flight, the balloon drifted over a huge cloud deck. There, the observed radiance provides a determination of the optical thickness of the cloud, and the polarization ratio is illustrative of scattering by large cloud droplets.
Liquid aerosols produced in many manufacturing and refining processes need to be filtered from the exhaust streams. Where wettable fibers are used in the filters, the aerosol liquid collects on the fibers. Observation...
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Liquid aerosols produced in many manufacturing and refining processes need to be filtered from the exhaust streams. Where wettable fibers are used in the filters, the aerosol liquid collects on the fibers. Observation shows that thin films develop on the fibers, and the liquid drains down the fibers under the action of gravity. A model is developed for the flow of liquid in these films, and careful experimentation confirms the nature and importance of the flow pattern. The resultant overall efficiencies of the filter are also calculated from a theoretical analysis and compared with the results of experimentation using counting techniques. The theoretical and experimental results agree excellently for the range of aerosol sizes that are detectable by laser diffraction and cascade impactor techniques.
Four Nuclepore filters with a pore size of 3.0, 5.0, 8.0 and 10.0-mu-m were tested at flow velocity in the range 4.2-25.0 cm/s. Ultrafine chain aggregates were used as a model fibrous aerosol. Experiments were carried...
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Four Nuclepore filters with a pore size of 3.0, 5.0, 8.0 and 10.0-mu-m were tested at flow velocity in the range 4.2-25.0 cm/s. Ultrafine chain aggregates were used as a model fibrous aerosol. Experiments were carried out under the condition that the collection mechanisms by diffusion and inertia were not significant. Results indicated that the collection efficiency decreased with flow velocity. The effects of dynamic shape, slip correction, and orientation distribution of the fibrous particles on collection mechanisms - diffusion, inertia impaction, and interception - are discussed.
The climate response to an abrupt increase of black carbon (BC) aerosols is compared to the standard CMIP5 experiment of quadrupling CO2 concentrations in air. The global climate model NorESM with interactive aerosols...
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The climate response to an abrupt increase of black carbon (BC) aerosols is compared to the standard CMIP5 experiment of quadrupling CO2 concentrations in air. The global climate model NorESM with interactive aerosols is used. One experiment employs prescribed BC emissions with calculated concentrations coupled to atmospheric processes (emission-driven) while a second prescribes BC concentrations in air (concentration-driven) from a precalculation with the same model and emissions, but where the calculated BC does not force the climate dynamics. The difference quantifies effects of feedbacks between airborne BC and other climate processes. BC emissions are multiplied with 25, yielding an instantaneous top-of-atmosphere (TOA) radiative forcing (RF) comparable to the quadrupling of atmospheric CO2. A radiative kernel method is applied to estimate the different feedbacks. In both BC runs, BC leads to amuch smaller surface warming than CO2. Rapid atmospheric feedbacks reduce the BC-induced TOA forcing by approximately 75% over the first year (10% for CO2). For BC, equilibrium is quickly re-established, whereas for CO2 equilibration requires a much longer time than 150 years. Emission-driven BC responses in the atmosphere are much larger than the concentration-driven. The northward displacement of the intertropical convergence zone (ITCZ) in the BC emission-driven experiment enhances both the vertical transport and deposition of BC from Southeast Asia. The study shows that prescribing BC concentrations may lead to seriously inaccurate conclusions, but other models with less efficient transport may produce results with smaller differences.
The coagulation rate of uncharged NaCl aerosols with mean particle radii of 25 and 45 A. was measured by means of a flow method: the aerosol was passed through a pipe and the ratio of particle concentrations at the in...
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The coagulation rate of uncharged NaCl aerosols with mean particle radii of 25 and 45 A. was measured by means of a flow method: the aerosol was passed through a pipe and the ratio of particle concentrations at the inlet and the outlet of the pipe was measured nephelometrically after “developing” the particles by condensing DBP vapor on them. Corrections for particle losses due to diffusion to the walls of the pipe were estimated in separate experiments with diluted aerosols. The absolute value of the particle concentration was determined by ultramicroscopic counting of developed aerosols. The average residence time of the aerosols in the pipe, i.e. , the coagulation time, was measured by means of a coarse oil mist. Experimental values 13.4 × 10 −10 and 15.0 × 10 −10 cm. 3 /sec. were obtained for the coagulation constant of the aerosols with r = 25 and 45 A., respectively. The values calculated by means of the formula for the number of collisions between gas molecules, taking into account the molecular attraction forces between the particles, are 10.5 × 10 −10 and 14.1 × 10 −10 cm. 3 /sec., respectively.
Fresh advances in the interpretation of spray monitoring data obtained from rotary slide samplers are outlined A predictive computer programme permits volumetric spray measurements to be converted to the most probable...
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Fresh advances in the interpretation of spray monitoring data obtained from rotary slide samplers are outlined A predictive computer programme permits volumetric spray measurements to be converted to the most probable insecticide dose received by tsetse flies resting adjacent to the samplers. Some applications to data collected during recent spray operations in Zimbabwe and Somalia are discussed.
Sahel precipitation has undergone substantial multidecadal time scale changes during the twentieth century that have had severe impacts on the region's population. Using initial-condition large ensembles (LE) of c...
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Sahel precipitation has undergone substantial multidecadal time scale changes during the twentieth century that have had severe impacts on the region's population. Using initial-condition large ensembles (LE) of coupled general circulation model (GCM) simulations from two institutions, forced multidecadal variability is found in which Sahel precipitation declines from the 1950s to 1970s and then recovers from the 1970s to 2000s. This forced variability has similar timing to, but considerably smaller magnitude than, observed Sahel precipitation variability. Isolating the response using single forcing simulations within the LEs reveals that anthropogenic aerosols (AA) are the primary driver of this forced variability. The roles of the direct-atmospheric and the ocean-mediated atmospheric responses to AA forcing are determined with the atmosphere-land GCM (AGCM) components of the LE coupled GCMs. The direct-atmospheric response arises from changes to aerosol and precursor emissions with unchanged oceanic boundary conditions while the ocean-mediated response arises from changes to AA-forced sea surface temperatures and sea ice concentrations diagnosed from the AA forced LE. In the AGCMs studied here, the direct-atmospheric response dominates the AA-forced 1970s 2 1950s Sahel drying. On the other hand, the 2000s 2 1970s wetting is mainly driven by the ocean-mediated effect, with some direct atmospheric contribution. Although the responses show differences, there is qualitative agreement between the AGCMs regarding the roles of the direct-atmospheric and ocean-mediated responses. Since these effects often compete and show nonlinearity, the model dependence of these effects and their role in the net aerosol-forced response of Sahel precipitation need to be carefully accounted for in future model analysis.
Lead concentrations in atmospheric particulate matter, along the southern coast of the Strait of Dover have been measured during two sampling campaigns, over a 10 year period. The results point out that lead concentra...
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Lead concentrations in atmospheric particulate matter, along the southern coast of the Strait of Dover have been measured during two sampling campaigns, over a 10 year period. The results point out that lead concentrations have been decreased by a factor of two, from 1982/83 to 1994. This evolution is in good agreement with a general trend to the diminution of lead in atmospheric aerosols above the Eastern Channel and the Southern Eight of the North Sea. It appears that, from 1972 to 1994, lead concentrations have decreased by an order of magnitude, despite the uncertainty of the oldest values. As established in a similar coastal environment, this decrease in the lead concentrations can be explained by the reduction in the emissions of automotive lead. The evolution of the mass-size distribution is consistent with this last factor;assuming that automotive lead is essentially present in particles smaller than 0.33 mu m, the observed decrease of this granulometric class between 1983 and 1994 (7 ng/m(3)) is close to the measured decrease in the lead concentrations (9 ng/m(3)). A slight decrease (14%) of the related dry deposition flux has been calculated for the same period. But, if part of the fall-out due to particles larger than 1 mu m is approximately constant over the same period (about 430 g/km(2) per year), the submicronic flux exhibits a decrease of 70%.
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