Abstract. Sunlit snow is highly photochemically active and plays a key role in the
exchange of gas phase species between the cryosphere and the atmosphere.
Here, we investigate the behaviour of two selected species in surface snow:
mercury (Hg) and iodine (I). Hg can deposit year-round and accumulate in the
snowpack. However, photo-induced re-emission of gas phase Hg from the
surface has been widely reported. Iodine is active in atmospheric new
particle formation, especially in the marine boundary layer, and in the
destruction of atmospheric ozone. It can also undergo photochemical
re-emission. Although previous studies indicate possible post-depositional
processes, little is known about the diurnal behaviour of these two species
and their interaction in surface snow. The mechanisms are still poorly
constrained, and no field experiments have been performed in different
seasons to investigate the magnitude of re-emission processes Three sampling
campaigns conducted at an hourly resolution for 3 d each were carried out
near Ny-Ålesund (Svalbard) to study the behaviour of mercury and iodine
in surface snow under different sunlight and environmental conditions
(24 h darkness, 24 h sunlight and day–night cycles). Our results indicate a
different behaviour of mercury and iodine in surface snow during the
different campaigns. The day–night experiments demonstrate the existence of a
diurnal cycle in surface snow for Hg and iodine, indicating that these
species are indeed influenced by the daily solar radiation cycle.
Differently, bromine did not show any diurnal cycle. The diurnal cycle also
disappeared for Hg and iodine during the 24 h sunlight period and during
24 h darkness experiments supporting the idea of the occurrence (absence) of
a continuous recycling or exchange at the snow–air interface. These results
demonstrate that this surface snow recycling is seasonally dependent,
through sunlight. They also highlight the non-negligible role that snowpack
emissions have on ambient air concentrations and potentially on
iodine-induced atmospheric nucleation processes.
Bismuth-based (nano)materials have
been attracting increasing interest
due to appealing properties such as high refractive indexes, intrinsic
opacity, and structural distortions due to the stereochemistry of
6s2 lone pair electrons of Bi3+. However, the
control over specific phases and strategies able to stabilize uniform
bismuth-based (nano)materials is still a challenge. In this study,
we employed the ability of bismuth to lower the melting point of silica
to introduce a new synthetic approach able to confine the growth of
bismuth-oxide-based materials into nanostructures. Combining in situ
temperature-dependent synchrotron radiation X-ray powder diffraction
(XRPD) with high-resolution transmission electron microscopy (HR-TEM)
analyses, we demonstrate the evolution of a confined Bi2O3–SiO2 nanosystem from Bi2SiO5 to Bi4Si3O12 through
a melting process. The silica shell acts as both a nanoreactor and
a silicon source for the stabilization of bismuth silicate glass-ceramic
nanocrystals keeping the original spherical shape. The exciton peak
of Bi2SiO5 is measured for the first time allowing
the estimation of its real energy gap. Moreover, based on a detailed
spectroscopic investigation, we discuss the potential and the limitations
of Nd3+-activated bismuth silicate systems as ratiometric
thermometers. The synthetic strategy introduced here could be further
explored to stabilize other bismuth-oxide-based materials, opening
the way toward the growth of well-defined glass-ceramic nanoparticles.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.