The Urmia Playa as source of airborne dust and ice nucleating particles – Part 1: Correlation between soils and airborne samples

Abstract

Abstract. The emergence of desiccated lakebed sediments and their exposure to wind erosion as a consequence of climate change and drought in arid and semiarid regions of the world poses a growing hazard. Airborne dust originating from such soils can create health and environmental issues due to their high salt content and the presence of toxic elements. The aim of the present study is twofold, namely to investigate the newly emerged playa surfaces of the western Lake Urmia (LU) in Iran and their contribution to aerosol in the region by means of physicochemical, mineralogical and elemental analyses, and to study the ice nucleation (IN) activity of both surface-collected soil and airborne dust samples. The playa surfaces created by desiccation of LU on the west shores were mapped and sampled at 130 locations. Soil samples were subjected to physicochemical analyses and their erodible fraction was determined. Based on these analyses, four highly erodible playa surfaces from northwest to the south of LU were selected as sites for collection of dust by impaction and soil samples from the uppermost surface. Their particle physicochemical properties (size distribution, elemental and mineralogical composition) were compared with their IN activity determined by emulsion freezing experiments in a differential scanning calorimeter (DSC) in two suspension concentrations of 2 wt % and 5 wt %. The physicochemical soil properties differed significantly between the different playa surfaces, which affects their susceptibility to wind erosion. Sand sheets and sandy salt crusts were the most erodible playa surfaces due to their high sand fraction, low organic matter and clay content, favoring the presence of small aggregates. Mineralogical analyses document the prevalence of quartz, carbonates and clay minerals such as kaolinite, palygorskite and chlorite in all of the samples. The predominant elements in the samples are Ca, Fe, Al, Si and Na and in some cases Ba, Sr and Zn. The correlation between soil and dust samples based on mineralogical composition, elemental enrichment factors, and physicochemical properties confirm that the playa surfaces are the major contributors to dust in the region. IN activity with onset temperatures ranging from 245 to 250 K demonstrates the high potential of dust blown from Urmia playa surfaces to affect cloud properties and precipitation. Freezing onset temperatures and the fraction of heterogeneously frozen droplets in the emulsions reveal variations in IN activity depending on the mineralogical composition of the samples, but also influenced by organic matter, salinity and pH. Specifically, IN activity correlates positively with organic matter and clay minerals, and negatively with pH and salinity, and, surprisingly, also negatively with K-feldspar and quartz content. The high wind erodibility and dust production of the LU playa surfaces together with their high IN activity can play an important role in the climate of the region and thus needs careful monitoring and specific attention.

The Urmia Playa as source of airborne dust and ice nucleating particles – Part 2: Unraveling the relationship between soil dust composition and ice-nucleation activity

“…A detailed characterization of the samples has been given and discussed in Part 1 of this work (Hamzehpour et al, 2022). Here, we summarize the applied methods and replicate the findings with relevance for this study.…”

“…The mineralogical composition of the bulk dust samples and surface collected soil samples was investigated with X-ray diffraction (XRD) analysis (Bish and Plötze 2010) followed by quantitative Rietveld analysis. More details are given in Part 1 (Hamzehpour et al, 2022). We replicate the results in Table 3.…”

“…The sampling procedure has been described in detail in Part 1 of this work (Hamzehpour et al, 2022). Here, we recapitulate the relevant information for the present study.…”

“…In order to investigate the role of salt type and concentration, and pH on the IN activity of microcline and quartz, we performed experiments with a microcline sample from North Macedonia (the same as has been used in Klumpp et al, 2022), and a quartz sample from Sigma Aldrich (the same as has been used in Kumar et al, 2019a) with 2 wt % and 1 wt % concentrations, respectively.…”

“…In the companion paper of this work (Hamzehpour et al, 2022), we identified highly erodible playa surfaces along the western Lake Urmia Playa (LUP), and characterized four surface-collected soil samples together with airborne dust samples from nearby meteorological stations with respect to physicochemical properties, mineralogical composition, and IN activity. Emulsion freezing experiments in a differential scanning calorimeter (DSC) revealed that some of the lower concentrated suspensions of the dust samples (2 wt %) exhibited a higher heterogeneously frozen fraction (Fhet) of droplets than the higher concentrated samples (5 wt %).…”