Abstract. Ternary homogeneous nucleation (THN) of [NH 3 ] are 3-5, 1-4, and 1, respectively. These slopes and the threshold of [H 2 SO 4 ] required for the unity nucleation vary only fractionally in the presence and absence of NH 3 . These observations can be used to improve aerosol nucleation models to assess how man-made SO 2 and NH 3 affect aerosol formation and CCN production at the global scale.

Abstract. This study presents a chemical ionization mass spectrometer (CIMS) for fast response, in-situ measurements of gas phase ammonia (NH 3 ). The NH 3 background level detected with the CIMS ranged between 0.3-1 ppbv, with an uncertainty of 30 pptv under optimized conditions. The instrument sensitivity varied from 4-25 Hz/pptv for >1 MHz of reagent ion signals (protonated ethanol ions), with a 30% uncertainty estimated based on variability in calibration signals. The CIMS detection limit for NH 3 was ∼60 pptv at a 1 min integration time (3 sigma). The CIMS time response was <30 s. This new NH 3 -CIMS has been used for ambient measurements in Kent, Ohio, for several weeks throughout three seasons. The measured NH 3 mixing ratios were usually at the sub-ppbv level and higher in spring (200 ± 120 pptv) than in winter (60 ± 75 pptv) and fall (150 ± 80 pptv). High emissions of SO 2 from power plants in this region, and thus possible high acidity of aerosol particles, may explain these low NH 3 mixing ratios in general.

Abstract. We studied experimentally a new phenomenon of turbulent thermal diffusion of particles which can cause formation of the large-scale aerosol layers in the vicinity of the atmospheric temperature inversions. This phenomenon was detected experimentally in oscillating grids turbulence in air flow. Three measurement techniques were used to study turbulent thermal diffusion in strongly inhomogeneous temperature fields, namely Particle Image Velocimetry to determine the turbulent velocity field, an image processing technique to determine the spatial distribution of aerosols, and an array of thermocouples for the temperature field. Experiments are presented for both, stably and unstably stratified fluid flows, by using both directions of the imposed mean vertical temperature gradient. We demonstrated that even in strongly inhomogeneous temperature fields particles in turbulent fluid flow accumulate at the regions with minimum of mean temperature of surrounding fluids due to the phenomenon of turbulent thermal diffusion.

Coherent large-scale circulations of turbulent thermal convection in air have been studied experimentally in a rectangular box heated from below and cooled from above using Particle Image Velocimetry. The hysteresis phenomenon in turbulent convection was found by varying the temperature difference between the bottom and the top walls of the chamber (the Rayleigh number was changed within the range of $10^7 - 10^8$). The hysteresis loop comprises the one-cell and two-cells flow patterns while the aspect ratio is kept constant ($A=2 - 2.23$). We found that the change of the sign of the degree of the anisotropy of turbulence was accompanied by the change of the flow pattern. The developed theory of coherent structures in turbulent convection (Elperin et al. 2002; 2005) is in agreement with the experimental observations. The observed coherent structures are superimposed on a small-scale turbulent convection. The redistribution of the turbulent heat flux plays a crucial role in the formation of coherent large-scale circulations in turbulent convection.Comment: 10 pages, 9 figures, REVTEX4, Experiments in Fluids, 2006, in pres

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