AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
An Experimental Assessment of the Dissociation of Ammonium Nitrate Aerosol
NICHOLAS TALBOT, Vladimir Zdimal, Jakub Ondrecek, Jaroslav Schwarz, PhD candidate
Abstract Number: 574 Working Group: Indoor Aerosols
Abstract The dissociation kinetics of ammonium nitrate was investigated experimentally utilizing a tandem differential mobility analyzer/scanning mobility particle sizer system (Dassios and Pandis, 1998). Monodisperse aerosol of ammonium nitrate has been produced by nebulizing ammonium nitrate solution, drying the polydisperse particles, bringing them to Boltzmann charge equilibrium using a Kr85 aerosol neutralizer, and selecting one mobility fraction in the Vienna type DMA. The aerosol generation system was located in a thermally insulated box kept at controlled temperature below 10 degrees C. The monodisperse aerosol was then diluted by mixing it with a dry, particle-free air and fed into a laminar flow reactor in which temperature, relative humidity and flow rate were controlled.
Particle size distributions both upstream and downstream of the reactor were determined by an SMPS, consisting of a TSI EC 3080 provided with a long DMA, and a TSI CPC 3775. The stability of the aerosol generating system was further checked by the UCPC 3025A monitoring continuously the total particle concentrations.
In the series of dissociation experiments, we studied the size changes of the ammonium nitrate aerosol for three selected particle sizes (50, 100 and 200 nanometres), at four reactor temperatures (15, 20, 25, and 30 degrees C), and several flow rates (between 0.6 to 1.6 litres per minute).
The observed changes of particle size were compared to the predictions of a mathematical model taking into account the ammonium nitrate dissociation kinetics, Kelvin effect and diffusion of ammonia and nitric acid from the particle to the bulk phase taking into account the measured concentration of ammonia gas in the bulk phase. The model assumed evaporation in the continuum regime using the Fuchs-Sutugin correction term (Wexler and Seinfeld, 1990). Two cases are considered in relation to the evaporation process, evaporation from an ammonium nitrate solution and evaporation from a dry ammonium nitrate particle.
The authors acknowledge support of this work by European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 315760 HEXACOMM.
References.
Dassios, K.G and Pandis, S.N, 1998, The mass accommodation coefficient of ammonium nitrate aerosol, Atmospheric Environment, 33, 2993-3003.
Wexler, A.S., Seinfeld, J.H., 1990. The distribution of ammonium salts among a size and composition dispersed aerosol, Atmospheric Environment 24, 12331- 12 346.