Measurement report: The Urmia playa as a source of airborne dust and ice-nucleating particles – Part 1: Correlation between soils and airborne samples
Authors: Hamzehpour Nikou , Marcolli Claudia , Pashai Sara , Klumpp Kristian , Peter Thomas 
Published: November 2022

Abstract. The emergence of desiccated lake bed 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
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 western 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 the 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 and low organic matter and clay content, favouring 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 which are also
influenced by organic matter, salinity, and pH. Specifically, IN activity
correlates positively with organic matter and clay minerals and negatively
with pH, salinity, and (surprisingly) 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.