Temperature-Dependent Diffusion of H2SO4 in Air at Atmospherically Relevant Conditions: Laboratory Measurements Using Laminar Flow Technique.

0477106 - ÚCHP 2018 RIV CH eng J - Journal Article
Brus, David - Škrabalová, Lenka - Herrmann, E. - Olenius, T. - Trávníčková, Tereza - Makkonen, U. - Merikanto, J.
Temperature-Dependent Diffusion of H2SO4 in Air at Atmospherically Relevant Conditions: Laboratory Measurements Using Laminar Flow Technique.
Atmosphere. Roč. 8, č. 7 (2017), č. článku 132. E-ISSN 2073-4433
R&D Projects: GA ČR GAP209/11/1342
Grant - others:ERC(FI) 257360; AFCE(FI) 272041; GA AF(FI) 288440
Institutional support: RVO:67985858
Keywords : diffusion coefficient * sulfuric acid * laminar flow tube
OECD category: Physical chemistry
Impact factor: 1.704, year: 2017

We report flow tube measurements of the effective sulfuric acid diffusion coefficient at ranges of different relative humidities (from similar to 4 to 70%), temperatures (278, 288 and 298 K) and initial H2SO4 concentrations (from 1 x 10(6) to 1 x 10(8) molecules.cm(-3)). The measurements were carried out under laminar flow of humidified air containing trace amounts of impurities such as amines (few ppt), thus representing typical conditions met in Earth's continental boundary layer. The diffusion coefficients were calculated from the sulfuric acid wall loss rate coefficients that were obtained by measuring H2SO4 concentration continuously at seven different positions along the flow tube with a chemical ionization mass spectrometer (CIMS). The wall loss rate coefficients and laminar flow conditions were verified with additional computational fluid dynamics (CFD) model FLUENT simulations. The determined effective sulfuric acid diffusion coefficients decreased with increasing relative humidity, as also seen in previous experiments, and had a rather strong power dependence with respect to temperature, around proportional to T-5.6, which is in disagreement with the expected temperature dependence of similar to T-1.75 for pure vapours. Further clustering kinetics simulations using quantum chemical data showed that the effective diffusion coefficient is lowered by the increased diffusion volume of H2SO4 molecules via a temperature-dependent attachment of base impurities like amines. Thus, the measurements and simulations suggest that in the atmosphere the attachment of sulfuric acid molecules with base molecules can lead to a lower than expected effective sulfuric acid diffusion coefficient with a higher than expected temperature dependence.
Permanent Link: http://hdl.handle.net/11104/0273492