Temperature-dependent diffusion coefficient of H2SO4 in air: laboratory measurements using laminar flow technique
- 1Finnish Meteorological Institute, Erik Palménin aukio 1, P.O. Box 503, FIN-00100 Helsinki, Finland
- 2Laboratory of Aerosols Chemistry and Physics, Institute of Chemical Process Fundamentals Academy of Sciences of the Czech Republic, Rozvojova 135, CZ-165 02 Prague 6, Czech Republic}
- 3Department of Physical Chemistry, Faculty of Science, Charles University in Prague, Hlavova 8, Prague, 128 43, Czech Republic
- 4Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland
- 5Department of Physics, University of Helsinki, Gustaf Hällströmin katu 2 A, P.O. Box 64, FIN-00014 Helsinki, Finland
- 6Department of Multiphase Reactors, Institute of Chemical Process Fundamentals Academy of Sciences of the Czech Republic, Rozvojova 135, CZ-165 02 Prague 6, Czech Republic
- acurrent address: Department of Environmental Science and Analytical Chemistry (ACES) and Bolin Centre for Climate Research, Stockholm University, SE-10691 Stockholm, Sweden
Abstract. We report measurements of the diffusion coefficient of sulfuric acid in humidified air at a range of relative humidities (from ~4 to 70 %), temperatures (278, 288 and 298 K) and initial H2SO4 concentration (from 1 × 10e6 to 1 × 10e8 molec. cm−3). The diffusion coefficients were estimated from the sulfuric acid wall loss rate coefficients under laminar flow conditions. The flow conditions were verified with additional fluid dynamics model CFD-FLUENT simulations which also reproduced the loss rate coefficients very well at all three temperatures with the maximum difference of 7 % between the measured and simulated values. The concentration of H2SO4 was measured continuously with chemical ionization mass spectrometer (CIMS) at seven different positions along the flow tube. The wall losses of H2SO4 were determined from the slopes of fits to measured H2SO4 concentrations as a function of the position along the flow tube. The observed wall loss rate coefficients, and hence the diffusion coefficients, were independent of different initial H2SO4 concentrations and different total flow rates. However, the determined diffusion coefficients decreased with increasing relative humidity, as also seen in previous experiments, and had a rather strong power dependence of the diffusion coefficient with respect to temperature, around ∝T5.4, which is in disagreement with the expected temperature dependency of ~T1.75 observed for other gases and not tested before for sulfuric acid. The effect of relative humidity on the diffusion coefficient is likely due to stronger hydration of H2SO4 molecules and likely also due to the presence of trace impurities such as amines, possibly brought to the system by humidification. Clustering kinetics simulations using quantum chemical data suggest that also the strong temperature dependence of the observed diffusion coefficient might be explained by increased diffusion volume of H2SO4 molecules due to stronger clustering with base-impurities like amines.
David Brus et al.
David Brus et al.
David Brus et al.
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