The uptake of SO<sub>2</sub> on Saharan dust: a flow tube study

Abstract

Abstract. The uptake of SO 2 onto Saharan mineral dust from the Cape Verde Islands was investigated using a coated wall flow tube coupled to a mass spectrometer. The rate of loss of SO 2 to the dust coating was measured and uptake coefficients were determined using the measured BET surface area of the sample. The uptake of SO 2 , with an initial concentration between (2-40)×10 10 molecule cm −3 (0.62-12 µTorr), was found to be strongly time dependent over the first few hundred seconds of an experiment, with an initial uptake γ 0,BET of (6.6±0.8)×10 −5 (298 K), declining at longer times. The amount of SO 2 adsorbed on the dust samples was measured over a range of SO 2 concentrations and mineral dust loadings. The uptake of SO 2 was found to be up to 98% irreversible over the timescale of these investigations. Experiments were also performed at 258 K, at a relative humidity of 27% and at 298 K in the presence of ozone. The initial uptake and the amount of SO 2 taken up per unit area of BET dust surface was the same within error, irrespective of the conditions used; however the presence of ozone reduced the amount of SO 2 released back into the gas-phase per unit area once exposure of the surface ended. Multiple uptakes to the same surface revealed a loss of surface reactivity, which did not return if the samples were exposed to gas-phase water, or left under vacuum overnight. A mechanism which accounts for the observed uptake behaviour is proposed and numerically modelled, allowing quantitative estimates of the rate and amount of SO 2 removal in the atmosphere to be estimated. Removal of SO 2 by mineral dust is predicted to be significant at high dust loadings.

Impact of mineral dust on nitrate, sulfate, and ozone in transpacific Asian pollution plumes

“…Estimates for uptake on dry calcite range from 10 −4 to 0.1 for γ (HNO 3 ) (Goodman et al, 2000; Hanisch and Crowley, 2001), and 10 −4 to 4×10 −2 for γ (SO 2 ) (Usher et al, 2002;Ullerstam et al, 2003;Adams et al, 2005). Studies also show a marked increase in uptake rate with relative humidity for calcite, as uptake of water leads to enhanced ion mobility at the dust surface (Al-Hosney and Grassian, 2005;Vlasenko et al, 2006;Baltrusaitis et al, 2007a;Preszler-Prince et al, 2007;Liu et al, 2008).…”

Variability of aerosol optical properties in the Western Mediterranean Basin

“…A good correlation was observed also for fine sulfate particles with R 2 higher than 0.82 after excluding specific days highlighted by the orange boxed areas. In these specific days the high measured scattering coefficients were likely due to high concentrations of coarse crustal particles (<C> PM 10 = 8.5±12.7 µg m −3 ) which favoured the 4 > PM 10 = 2.0±0.9 µg m −3 ), thus increasing the scattering (Vrekoussis et al, 2005;Adams et al, 2005). In fact, the mean <C> PM 10 and <SO 2− 4 > PM 10 calculated over the points included in the fitting process were 1.7±1.2 µg m −3 and 0.7±0.5 µg m −3 , respectively.…”

The impact of dust on sulfate aerosol, CN and CCN during an East Asian dust storm

“…Heterogeneous reactions between acidic gases (e.g., SO 2 , H 2 SO 4 , HNO 3 ) and dust have been examined extensively in the laboratory (Adams et al, 2005;Goodman et al, 2001;Li et al, 2006;Ullerstam et al, 2002Ullerstam et al, , 2003Usher et al, 2002;Prince et al, 2007), but the mechanism and rate at which inorganic ions form on dust remain uncertain. In this study…”