Development and Characterization of a Fast-Stepping/Scanning Thermodenuder for Chemically-Resolved Aerosol Volatility Measurements

Abstract

A thermodenuder (TD) system, based on the design of Wehner et al. (2002), was designed, constructed, and characterized in the laboratory. The TD consists of a heated tube (2.5 cm ID, 55 cm long) held at a constant temperature by a 3-zone controller, followed by a cooling zone with a diffusion tube lined with activated charcoal for adsorption of evaporated gases. An important improvement over previous designs is the ability to step through TD temperatures in ∼10 min. per step by the reduction of thermal inertia, and the addition of two cooling fans. The TD was characterized in the laboratory, showing that temperature profiles inside are relatively uniform and for response to standard generated particle species. Losses at ambient temperature are close to diffusion losses estimated with literature techniques and to those experimentally measured by Wehner et al. Particle number losses are observed to increase for volatile species upon heating due to particles shrinking to sizes where diffusion and thermophoresis are more efficient. The thermodenuder was placed upstream of an Aerodyne Aerosol Mass Spectrometer (AMS) during several field experiments. An automated valve system was designed and built to allow rapidly alternating data points between thermodenuder-processed aerosol and un-processed aerosol. This system has enabled the rapid (1-3 h) collection of chemically-resolved volatility over the range of

Toward the Determination of Joint Volatility-Hygroscopicity Distributions: Development and Response Characterization for Single-Component Aerosol

“…A thermodenuder was constructed based on the original design of Wehner et al (2002) and modifications of Huffman et al (2008) (Figure 1). The instrument consists of a heating section, which allows semi-volatile components in the aerosol to volatilize, followed by a cooling section where the volatilized gas components are adsorbed onto activated carbon before exiting the instrument.…”

“…Several thermodenuder designs have been presented and analyzed in the literature (Burtscher et al 2001;Wehner et al 2002;297 An et al 2007;Fierz et al 2007;Huffman et al 2008;Faulhaber et al 2009). Design parameters involve the residence time in the heating section Fierz et al 2007;Saleh et al 2011), the temperature profile in the heating section (Huffman et al 2008;Faulhaber et al 2009), the effectiveness of the cooling section (Fierz et al 2007;Saleh et al 2011;Fuentes and McFiggans 2012), and the modeling approach used to interpret the data (Saleh and Shihadeh 2007;Cappa 2010;Riipenen et al 2010;Saleh et al 2011).…”

“…Generally, the thermodenuder geometry and instrument flow rate are selected to give a desired residence time in the heating section of the thermodenuder. Attention has also been given to characterizing temperature profiles that develop in the heating section through, for example, the use of sand as insulating material (Wehner et al 2002) and multiple heating zones (Huffman et al 2008;Faulhaber et al 2009). Studies by Saleh et al (2011) and Fuentes and McFiggans (2012) have investigated the level of importance of the cooling section and the influence of mass loading on the re-condensation fraction of volatilized material.…”

“…Design parameters involve the residence time in the heating section Fierz et al 2007;Saleh et al 2011), the temperature profile in the heating section (Huffman et al 2008;Faulhaber et al 2009), the effectiveness of the cooling section (Fierz et al 2007;Saleh et al 2011;Fuentes and McFiggans 2012), and the modeling approach used to interpret the data (Saleh and Shihadeh 2007;Cappa 2010;Riipenen et al 2010;Saleh et al 2011). Generally, the thermodenuder geometry and instrument flow rate are selected to give a desired residence time in the heating section of the thermodenuder.…”

“…Together with the aerosol concentration flowing through the instrument and the degree to which gas-particle equilibrium is satisfied in the thermodenuder influences how approximations affect the inferred volatility distributions. Cappa (2010) and Lee et al (2010) approximate the thermodenuder temperature with a piecewise profile with constant radial temperature based on the experimental temperature profile of Huffman et al (2008). Riipinen et al (2010) assume a constant temperature throughout the thermodenuder.…”