The effect of low solubility organic acids on the hygroscopicity of sodium halide aerosols

Abstract

Abstract. In order to accurately assess the influence of fatty acids on the hygroscopic and other physicochemical properties of sea salt aerosols, hexanoic, octanoic or lauric acid together with sodium halide salts (NaCl, NaBr and NaI) have been chosen to be investigated in this study. The hygroscopic properties of sodium halide sub-micrometre particles covered with organic acids have been examined by Fourier-transform infrared spectroscopy in an aerosol flow cell. Covered particles were generated by flowing atomized sodium halide particles (either dry or aqueous) through a heated oven containing the gaseous acid. The obtained results indicate that gaseous organic acids easily nucleate onto dry and aqueous sodium halide particles. On the other hand, scanning electron microscopy (SEM) images indicate that lauric acid coating on NaCl particles makes them to aggregate in small clusters. The hygroscopic behaviour of covered sodium halide particles in deliquescence mode shows different features with the exchange of the halide ion, whereas the organic surfactant has little effect in NaBr particles, NaCl and NaI covered particles experience appreciable shifts in their deliquescence relative humidities, with different trends observed for each of the acids studied. In efflorescence mode, the overall effect of the organic covering is to retard the loss of water in the particles. It has been observed that the presence of gaseous water in heterogeneously nucleated particles tends to displace the cover of hexanoic acid to energetically stabilize the system.

Complete Bromide Surface Segregation in MixedNaCl/NaBrAerosols Grown from Droplets

“…As the salt concentration in the droplets increases because of the evaporation of water, it reaches saturation and crystallization will commence. The efflorescence points for NaCl and NaBr are 45% [13] and 23% [45], respectively. For NaCl nanoparticles with diameters larger than 40 nm, the efflorescence point is similar to that of the bulk [13].…”

“…This can be accomplished by either vertical or horizontal (inland) transport. Under the drying conditions used here, the relative humidity at the outlet of the dryers is 8% and thus significantly below the efflorescence points for both NaCl (45% [13]) and NaBr (23% [45]) and assures a thorough drying. The lack of signal in the O 1s x-ray absorption region provides additional proof for the dryness of solid aerosols.…”

Experimental observation of structural phase transition in CsBr clusters

“…The structure and chemical properties can play important roles for aerosol-water interactions. Varying water uptake on aerosol particles mixed with different marine halides [2] may be linked to different propensities of the halides for the immediate aqueous interface. Although sea salt aerosols are generally mixtures of different inorganic salts, pure component structural information is a crucial first step to assess the water interaction potential of different sea salt components and in particular investigate the possibly much enhanced role of the less abundant components.…”

The role of marine aerosol in the formation of (double) sulfate/nitrate salts in plasters

“…Sometimes NaCl, MgCl 2 , CaCl 2 solutions can dehydrate gypsum as a result of the lower water vapour pressure of these solutions, modifying its solubility [8]. The later compounds, together with nitrates and sulfates, are present in marine aerosol [9], besides of fatty acids [10]. Some authors point out that in marine aerosol a mixture of ions like Na + , Ca 2+ , Mg 2+ , K + , Cl − , Br − , I − , Li + , NO 3 − , NH 4 + , SO 4 2 − and CO 3 2 − are usually present along with which can occur in natural environment, promoting the formation of different type of sulfates.…”