Water Interaction with Mineral Dust Aerosol: Particle Size and Hygroscopic Properties of Dust

Transcription

1 Water Interaction with Mineral Dust Aerosol: Particle Size and Hygroscopic Properties of Dust Sara Ibrahim, 1 Manolis N. Romanias*, 1 Laurent Y. Alleman, 1 Mohamad N. Zeineddine, 1 Giasemi K. Angeli, 2 Pantelis N. Trikalitis, 2 Frederic Thevenet, 1 1 : IMT Lille Douai, Univ. Lille, SAGE - Département Sciences de l Atmosphère et Génie de l Environnement, Lille, France 2 : Department of Chemistry, University of Crete, Voutes, Heraklion, Greece * Corresponding author: Manolis N. Romanias, Tel.: +33 (0) ; Fax: +33 (0) ; emmanouil.romanias@imt-lille-douai.fr Number of pages (including this one): 10 Number of tables: 2 Number of figures: 6 S1

2 Specific surface area measurements. The specific surface area of the ATD samples is determined using gas sorption analysis. The instruments are equipped with pressure transducers for accurate pressure determination and vacuum pumps. Initially, a known mass of the sample is introduced into a quartz cell which is then adjusted to the sorption analyzer. Thereafter the sample is heated under vacuum for several hours. Subsequently, the sample is cooled down (always under vacuum) and then immersed into liquid nitrogen bath. The (SSA) of the collected dust samples is determined using pure nitrogen gas within the range of 0.05 to 0.3 relative pressure range. At the end of the experiment the mass of the sample is weighted again to determine any mass loss during the degassing procedure (variations less than 3 % are observed); S2

3 ATD samples (μm) Table S1. Statistics of the mean, median and modal size distribution, and specific surface area (m 2 g -1 ) of the various grades of ATD. Four nitrogen adsorption experiments were conducted for each sample using the laboratory sorption analyzer and values are in excellent agreement with those determined using the commercial Autosorb-1MP Quantachrome sorption analyzer. The average SSA and of the measurements using both techniques are provided. Specific surface area Size distribution Custom build Autosorb-1MP Mean Median Mode Number of measurement Mean a (μm) (μm) (μm) (m 2 g -1 (m 2 g -1 ) a ) ± ±1.7 Average b (m 2 g -1 ) ± ± ± ± ± ± ± ± a : errors correspond to the standard deviation of the measurements b : errors to the average values correspond to the extreme error limits of the measurements determined using the two complementary techniques. Table S2. The abundance (in %) of the principal elements (excluding O, C, H, N) determined with ICP- MS for each grade of ATD. For comparison purposes, the chemical composition of ATD 0-3 µm determined by Joshi et al. is provided. 1 Element (mass number) This study Joshi et al. This study 0-3 μm a 0-3 μm b 5-10 μm μm μm μm Si Al Fe Ca K Mg Na Ti Ba Mn Sr Sum (%) a : Collected in 2013 b : collected in 2010 S3

4 Figure S1. Size distribution of the various grades of ATD determined by the supplier using multisizer 3 Coulter particle size and count analyzer. S4

5 Figure S2. Evolution of Φ(n,x)/I ads as a function of θ(n,x) upon linearization of the 3-parameter BET equation (Equation 4). Solely the data using the water stretching mode band are presented. Constants I mono and c are respectively determined from the slope and intercept of the linear regression. Errors quoted correspond to the 2σ precision of the fit of experimental points. S5

6 Figure S3. Correlation of a) water monolayer formation threshold with the specific surface area of the ATD samples. The solid line corresponds to the linear fit of data points; b) water monolayer formation threshold with parameter n. Solid line is the linear fit of results; c) water adsorption enthalpy with the specific surface area of the different ATD grades. Solid line is the linear fit of results. Note that solely parameters determined using the water stretching mode band are presented. S6

7 Figure S4. Water monolayer formation threshold for the different ATD grades as a function of the ratio of the most abundant elements: a) Al/Si, b) Ca/Si and c) Fe/Si; other natural dust samples previously reported by Joshi et al., are integrated to the plot. S7

8 Figure S5. Temporal evolution of the integrated area (left axis) and the normalized integrated area corresponding to water monolayer (right axis) along a typical adsorption-desorption experiment for ATD 5-10 µm. The dust surface is exposed to RH level for monolayer formation (i.e. 17 % RH). Each data point corresponds to the integrated area of the water absorption band corresponding to the stretching vibration mode between cm -1, it proceeds from 16 co-added DRIFT spectra. S8

9 Figure S6. a) Desorption profiles of water as a function of time from the five different ATD grades. For clarity, the integrated areas of the water absorption bands are normalized. I r is the integrated area of the water adsorption band at a given time t, and I 0 is the integrated area under equilibrium conditions. The ratio I r /I 0 = 1 corresponds to monolayer. b) Plot of 1/n as a function of time (t) for each dust grade. Solely, the data points that corresponds to surface coverage three times higher than the non-recovered water surface concentration were considered. The second order desorption rate coefficient, k des, is determined from the slope of the linear square fit of the experimental results. ads(t) S9

10 References 1. Joshi, N.; Romanias, M. N.; Riffault, V.; Thevenet, F., Investigating water adsorption onto natural mineral dust particles: Linking DRIFTS experiments and BET theory. Aeolian Res. 2017, 27, S10