ABSORPTION OF GASES IN GROWING DROPLETS

The situation where a stationary droplet in a supersaturated medium is growing by condensation of a vapor and simultaneously absorbing a gas is theoretically analyzed to study the effect of growth on absorption rate. The absorption rate is assumed to be liquid phase diffusion controlled, and the unsteady state liquid phase diffusion equation with moving boundary has been solved by a similarity technique. The results indicate that for fast droplet growth rates, induced by relatively high degrees of supersaturation, the absorption rate is significantly enhanced, leading to higher solute concentration near the surface than that observed for a similar droplet of finite size. For slow growth rates, the results are not significantly different from the quasi-stationary results.     

Performance evaluation of a cyclone with granular packed beds

This paper presents the performance evaluation results of a cyclone packed with granules in the gas outlet and cone. The results showed that a cyclone packed with granules in the gas outlet enhances significantly the particle collection of all sizes at 10 lpm. However, at 30 and 50 lpm, the granules increase only the collection efficiency of small particles, but decrease the collection of large particles to a small extent. In addition, the collection efficiency is higher with 2 mm granules than with 4 mm granules. The enhancement of collection efficiency, with granules in the gas outlet, was much more significant than with granules in the cone. Subsequently, this study showed that the granular cyclone could be used as a particle collector especially for small particles with low flow rate.     

H2 production by steam-quenching of Zn vapor in a hot-wall aerosol flow reactor

Hydrogen production by steam-hydrolysis of zinc is investigated as part of a two-step water-splitting thermochemical cycle based on ZnO/Zn redox reactions. The hydrolysis reactor consists of a hot-wall tube containing a flow of Zn(g) that is steam-quenched to co-produce H₂ and Zn/ZnO nanoparticles. The effects of the quenching gas flow rate and reactor wall temperature on the Zn-to-ZnO chemical conversion and particle yield are examined. Solid products are characterized by X-ray diffraction, N₂ adsorption, and SEM microscopy. Quench rates of 2-6×10⁴ K/s yielded conversions of up to 95% at the expense of low particle yield due to significant wall deposition with subsequent hydrolysis. Aerosol particles with hexagonal structure were formed by Zn evaporation-condensation containing low ZnO mass fraction. In contrast, operation at quench rates up to 10⁶ K/s led to increased particle yield but lower conversion. Filamentary and rod-like particles were formed with high ZnO content by surface reaction and coagulation.     

强效水基杀虫气雾剂的研究进展

目的通过调整料液的配比,制作出雾化良好、药效强劲的水基杀虫气雾剂。方法通过选用新型乳化剂等组分,达到以上目的。结果经过试验,其雾化良好,喷雾表面无泡沫,同时其药效与普通油基杀虫气雾剂相当。     

Ozonolysis of α-PINENE, β-PINENE,d- and l-Turpentine Oil Studied by Chirooptical Methods; Some Implications on the Atmospheric Chemistry of Biogenic Volatile Organic Compounds

The main constituents of biogenic volatile organic compounds (BVOC) released in the atmosphere from vegetation are terpenes. The most common terpenes are α-pinene and β-pinene. These molecules react with ozone, forming oxidized derivatives which have low vapor pressure and which nucleate into secondary organic aerosol (SOA). Such aerosol-forming reactions have been simulated in the gas phase on laboratory scale with the visualization of the formation of SOA. Electronic absorption spectroscopy shows that the UV peak of pinenes at 205 nm is shifted to 225 nm during and after ozonolysis and is accompanied by a series of spectral features in the near infrared region (between 850 nm and 1100 nm). Optical rotatory dispersion (ORD) spectra were recorded on pure β(+)pinene and β(?)pinene. After ozonolysis β-pinene enantiomers are converted into nopinone enantiomers. The ORD spectra of both (?)nopinone and (+)nopinone respectively were recorded. The former showed a peak at 453 nm, an inflection point at 430 nm and a trough at 405 nm. The ORD spectrum of (?)-nopinone appears completely symmetrical to that of (+)nopinone. Thus, ORD spectroscopy can distinguish between BVOC and oxidized BVOC quite easily at least in the case of β-pinene. The ORD spectra of α-pinene enantiomers are different from those of β-pinene enantiomers and although the ORD spectra of ozonized α-pinene are not easily distinguishable from those of the primary compounds, they are completely different from those of ozonized β-pinene enantiomers. A reasonable natural model of BVOC is offered by l- and d-turpentine oil whose composition reflects that of the BVOC from conifer forests. The ORD spectra of ozonized l- and d-turpentine has permitted to distinguish between the levorotatory and dextrorotatory oxidation products and showing the ketone peak at about 367–380 nm, thus permitting in a real model to distinguish between primary BVOC (turpentine) and oxidized BVOC (or SOA) corresponding to ozonized turpentine. It has been proposed that ORD spectra in the gas phase could be used to detect chiral BVOC and oxidized chiral BVOC.     

Simulation of aerosol dynamics and transport in chemically reacting particulate matter laden flows. Part I: Algorithm development and validation

To accurately predict aerosol dynamics in various systems, it is imperative to combine the governing equations for transport of momentum, mass and energy as well as reaction kinetics with an accurate procedure for solving the general dynamic equation (GDE). A generalized approach for solution of the GDE based on the discrete-sectional approach in presence of convective and molecular transport is presented. As computational efficiency is an important factor in realistic implementation of such a model, in Part-I of this two-part paper series an adaptive semi-implicit algorithm based on the concept of operating splitting is presented. It is shown that this algorithm is the method of choice for solving the GDE in presence or absence of convective transport based on a discrete-sectional approach.     

Remote sensing of aerosols optical thickness over various sites using SeaWiFS or VEGETATION and ground measurements

A key problem in aerosol retrieval is to distinguish between surface and atmospheric contributions to the variability in the satellite signal. A major contribution in the surface-related variability is caused by the non-Lambertian nature of the Earth surface reflectance and the fact that the illumination/observation geometry varies considerably between successive observations of the same area (with a polar orbiting sensor). In principle, if the surface boundary condition can be specified with sufficient accuracy by means of a bidirectional reflectance distribution function (BRDF), the two contributions can be unfolded and aerosol information retrieved. This approach has been tested using combined datasets made of satellite measured “top of atmosphere” (TOA) radiance and corresponding ground estimation of the aerosol optical thickness. Studying a time series of data, taking into account geometrical conditions and assuming the ground BRDF to be constant during the time period, a coupled surface/atmosphere model was used to investigate the retrieval of aerosol optical thickness (AOT) over several sites. By fitting a subset of satellite observations associated with ground photometer data, a best fit of BRDF model parameters could be determined. This surface characterization is then used to reduce the model unknowns to AOT only and thereby to permit its retrieval from the satellite data alone, by means of a simple inversion process. The study was conducted on three European AERONET sites and using satellite data from both the VEGETATION and Sea viewing Wide Field of view (SeaWiFS) sensors. In all cases, the AOT retrieved from satellite was in good agreement with the measurements.     

Ball Lightning–Aerosol Electrochemical Power Source or A Cloud of Batteries

Despite numerous attempts, an adequate theoretical and experimental simulation of ball lightning still remains incomplete. According to the model proposed here, the processes of electrochemical oxidation within separate aerosol particles are the basis for this phenomenon, and ball lightning is a cloud of composite nano or submicron particles, where each particle is a spontaneously formed nanobattery which is short-circuited by the surface discharge because it is of such a small size. As free discharge-shorted current loops, aerosol nanobatteries are exposed to a powerful mutual magnetic dipole–dipole attraction. The gaseous products and thermal energy produced by each nanobattery as a result of the intra-particle self-sustaining electrochemical reactions, cause a mutual repulsion of these particles over short distances and prevent their aggregation, while a collectivization of the current loops of separate particles, due to the electric arc overlapping between adjacent particles, weakens their mutual magnetic attraction over short distances. Discharge currents in the range of several amperes to several thousand amperes as well as the pre-explosive mega ampere currents, generated in the reduction–oxidation reactions and distributed between all the aerosol particles, explain both the magnetic attraction between the elements of the ball lightning substance and the impressive electromagnetic effects of ball lightning.     

Ultra-low gas sensing utilizing metal oxide thin films

The structure, functionality and sensing response of metal oxide films is discussed with emphasis on ZnO and InO_x prepared by Aerosol Spray Pyrolysis in ambient atmosphere and DC Magnetron Sputtering techniques under vacuum. Optical, structural and electrical characterization techniques applied for the in-depth analysis of the film properties are described. Sensing response towards ozone is presented utilizing a conventional conductivity technique as well as surface acoustic wave (SAW) structures and devices. It is shown that sensing responses of extremely low ozone concentrations in the range of a few parts per billion (ppb), at room temperature (RT), may be obtained by appropriate control of the film nanostructure. It is also shown that InO_x employed as sensitive layer on top of surface acoustic wave structures can lead to strong frequency shifts for low concentrations of NO₂, H₂ and O₃ gases.