Finnish Meteorological Institute, Erik Palménin aukio 1, P.O. Box 503, FIN-00100 Helsinki, Finland
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.
How to cite. Brus, D., Skrabalova, L., Herrmann, E., Olenius, T., Travnickova, T., and Merikanto, J.: Temperature-dependent diffusion coefficient of H2SO4 in air: laboratory measurements using laminar flow technique, Atmos. Chem. Phys. Discuss. [preprint], https://doi.org/10.5194/acp-2016-398, 2016.
Received: 11 May 2016 – Discussion started: 31 May 2016
We report laboratory measurements of the diffusion coefficient of sulfuric acid in humidified air. To our best knowledge, this is the first study, which investigates systematically the temperature dependency of the diffusion coefficient of H2SO4. We observed a rather strong power dependence with power of 5.4 when compared to 1.75 observed for other gases. We suggest that observed higher temperature dependence might be due to strong clustering of H2SO4 with base-impurities like amines.
We report laboratory measurements of the diffusion coefficient of sulfuric acid in humidified...