A method of predicting the particle removal efficiency of gravitational wet scrubbers and the particle size distribution properties, that considers diffusion, interception, and impaction, is presented to study the particle removal mechanisms of gravitational wet scrubbers. This method assumes a lognormal size distribution of aerosol particles as well as three additive collection efficiencies. Thus, the overall collection efficiency is described as the sum of all three. It is represented as a U-shaped curve with a minimum in the region of around 1.0 mm in particle diameter. This allows aerosols in the diffusion-and in the impactiondominant regions to be removed at a higher rate compared with aerosol in the intermediate region. As aerosols pass through the gravitational wet scrubber, the geometric standard deviations of the size distribution of polydispersed aerosols decrease. The geometric mean diameter of aerosol in the diffusion-dominant region increases, whereas it decreases in the impaction-dominant region. The present study also shows that in optimum operation conditions such as low droplet falling velocity, small droplet size, and high liquid-to-gas flow ratio, the gravitational wet scrubber has sufficient ability to remove particles whose diameters are much smaller than 1.0 mm.

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Cloud Condensation Nuclei (CCN) concentration and aerosol size distributions in the Arctic were collected during the period 2007-2013 at the Zeppelin observatory (78.91 N, 11.89 E, 474 masl). Annual median CCN concentration at a supersaturation (SS) of 0.4% show the ranges of 45 $ 81 cm À3 . The monthly median CCN number density varied between 17 cm À3 in October 2007 and 198 cm À3 in March, 2008. The CCN spectra parameters C (83 cm À3 ) and k (0.23) were derived. In addition, calculated annual median value of hygroscopicity parameter is 0.46 at SS of 0.4%. Particle number concentration of accumulation mode from aerosol size distribution measurements are well correlated with CCN concentration. The CCN to CN>10 nm (particle number concentration larger than 10nm in diameter) ratio shows a maximum during March and minimum during July. The springtime high CCN concentration is attributed to high load of accumulation mode aerosol transported from the mid-latitudes, known as Arctic Haze. CCN concentration remains high also during Arctic summer due to the source of new CCN through particle formation followed by consecutive aerosol growth. Lowest aerosol as well as CCN number densities were observed during Arctic autumn and early winter when aerosol formation in the Arctic and long-range transport into the Arctic are not effective.

ABSTRACT. The collection of small particles by a system consisting of multiple fluid spheres such as water droplets or gas bubbles was studied analytically. Kuwabara's free vorticity model based on the solid particle system was extended to include the effects of induced internal circulation inside a liquid droplet or gas bubble system on the flow and the mass transfer rate. Using the resolved flow field, analytic solutions were obtained for the particle collection efficiencies due to diffusion and interception. The results were applied to the problem of particle capture by gas bubbles in liquid or by droplets suspended in gas. The results indicated that the particle collection efficiency by the multiple fluid sphere system is higher than that by a solid sphere system. This is due to the internal circulation which develops inside the fluid spheres. AEROSOL SCIENCE AND TECHNOLOGY 29:389-401 (1998) O 1998 American Association for Aerosol Research NOMENCLATURE a = radius of sphere b = radius of boundary c, c' = dimensional and dimensionless transferred coordinate particle concentration c, = transferred coordinate particle concentrations at the outside boundary layer d, = diameter of the particle d, = diameter of the sphere D = particle diffusion coefficient E = overall particle collection efficiency L = length of collector system m = positive number M = dimensionless diffusion rate of particle to sphere M, = maximum value of M n, n' = dimensional and dimensionless particle concentration n,, n, = particle concentrations at outside boundary layer and at r = a Pe = Peclet number (= 2ualD)r, r' = d~mensional and dimensionless radial position coordinates u = flow velocity u,, u, = radial and circumferential components of flow velocity a = volume fraction, packing density, or solidity of packed bed 13, 6' = dimensional and dimensionless radii of boundary layer K W Lee and C. H. JungAerosol Science and Technology 29:5 November 1998 q = single sphere efficiency qD, qR = single particle collection efficiencies due to diffusion, interception pO, p1 = viscosity of fluids outer and inner boundary cr = viscosity ratio of inner to outer spheres (= p7p0) w = vorticity 5 = distance between center line and particle position in region far from collection sphere 8 = circumferential position coordinate

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