Abstract
It is increasingly recognized that light-absorbing impurities deposited
on a surface can reduce its albedo and lead to increased absorption of
solar radiation. Natural dust can travel substantial distances in the
Earth’s atmosphere from its original source. It affects all climatic
zones from the tropics to the poles and it may have a regional or global
impact on air quality and human health. In the Arctic, a rapid increase
in temperature compared to the global change, known as Arctic
Amplification, is closely linked to snow albedo feedback. Furthermore,
recent studies detail an extreme climate change scenario in the history
of our planet that lead to catastrophic cascading events and global mass
extinction triggered by atmospheric soot injections. Therefore,
knowledge of optical properties of dust particles is important for
improved climate models and dust effect studies. Here we report detailed
results of multi-angular polarized measurements of light scattered by
volcanic sand particles obtained with the FIGIFIGO goniospectrometer
(Peltoniemi et al. 2014). The design concept of this custom made
instrument has a well designed user friendly interface, a high level of
automation, and an excellent adaptability to a wide range of weather
conditions during field measurements. The foreoptics is connected to an
ASD FieldSpec Pro FR 350-2500 nm spectroradiometer by an optical fiber.
A calcite Glan-Thompson prism is used as a polarizer, covering the full
spectral range with better than 1% accuracy. The samples studied in
this work were collected from the Mýrdalssandur area in Iceland (in
March 2016) and from the Villarica area in Chile (in July 2019).
Following established FGI practices in laboratory conditions samples are
further divided into the following categories: (1) natural volcanic
sand, (2) sieved volcanic sand (dust) where the size of the particles is
less than 250 μm, including dry and wet sample condition, and (3) a
fine-grained powder of milled volcanic sand measurable also as aerosol.
The potential use of the results from our measurements are diverse,
including their use as a ground truth reference for Earth Observation
and remote sensing studies, estimating climate change over time, as well
as measuring other ecological effects caused by changes in atmospheric
composition or land cover.