Binary Homogenous Nucleation of Sulfuric Acid and Water Mixture: Experimental Device and Setup

Abstract

New particle formation in the atmosphere has received considerable attention lately both from atmospheric scientists and aerosol researchers. Atmospheric new particles have been observed to form by self-condensing or nucleating homogeneously in events lasting a couple of hours nearly all around the world (Kulmala et al., 2004). The first step of new particle formation or any first order phase transition is nucleation. It has been calculated that in the atmosphere the equilibrium vapor pressure of sulfuric acid is low enough for it to be a likely candidate to nucleate homogeneously, (e.g. Seinfeld and Pandis, 1998). All recent experiments on homogeneous sulfuric acid and water nucleation have relied on a flow-based measurement technique (e.g. Wyslouzil et al.1991, Viisanen et al., 1997, Ball et al., 1999, Zhang et al., 2004 and Berndt et al., 2006). In general the results are in fair agreement with each other, although somehow dependent on the method of generating the sulfuric acid vapor. A New laminar flow chamber built recently in Finnish Meteorological Institute is presented here. It is designed for homogeneous nucleation experiments of binary and ternary compounds such as sulfuric acid and water. The laminar flow chamber is positioned vertically and experimental setup consists of an atomizer, a furnace, a mixing unit, a nucleation chamber and measurement unit. A known amount of studied solution is introduced to furnace with HPLC Pump through a ruby micro-orifice (20 μm). The dispersion is then vaporized in a Pyrex glass tube wrapped with resistant heating wires. The furnace temperature is kept at 380 °C, and the temperature of vapor inside furnace is 235 °C. After furnace, the vapor is filtered with Teflon filter, introduced to mixing unite and cooled by turbulent mixing with particle free air to 60 °C. The vapor gas mixture is then cooled to wanted nucleation temperature in nucleating chamber which is kept at constant temperature with two liquid circulating baths. The nucleation chamber is made of stainless steel and its whole length is 200 cm. Temperature of the stream is registered along the nucleation chamber using six PT100 probes. For nucleation at room temperature, 25 °C is achieved at a distance approximately 115 cm from the mixing unit. The measured temperature profile is shown in Fig 1.