Environmental and space science

Combining materials chemistry, physics, and biology in multidisciplinary combinations offers the most effective way of meeting the challenges presented by climate change, environmental protection and the emergent demands of the low carbon economy. The agenda for Energy and the Environment is demanding new and improved catalysts, more efficient harvesting of light energy, efficient energy storage in batteries and fuel cells, and a better understanding of the fundamental processes that take place in the Earth, in the atmosphere and in space.

Environmental samples typically have a high degree of elemental and chemical heterogeneity in their composition that is closely related to environmental chemical speciation and mobility as well as the potential for incorporating pollutants and contaminants from their physical environment. Characterization of these heterogeneities is of primary importance in the area of environmental science, particularly in the new interdisciplinary area of environmental science christened molecular environmental science (MES) which studies chemical, biological, and geological processes occurring at environmentally relevant interfaces. Thus, from the early stage of MES, synchrotron-based spectroscopy has been recognized as an important analytical tool with several beamlines being available in major synchrotron facilities in the United States (e.g., SSRL, ALS, APS, NSLS). The VERSOX beamline will provide an equivalent soft x-ray facility for environmental scientists in the UK requiring access to x-ray photoelectron spectroscopy (XPS), X-ray electron, fluorescent and luminescence absorption spectroscopy (NEXAFS, FY-XAS and LY-XAS).

Astronomy is the oldest of the sciences, and it has received a spectacular boost in the last sixty years from observations outside the original optical waveband. The Universe which has been revealed continues to inspire deep questions regarding our origins, to which we have only partial answers. Current questions include: Where do planets come from? How did life originate? These are not purely philosophical questions, but issues that can be addressed by modern science.

Particulate matter

Identification of source specific signatures is of utmost importance for subsequent source attribution and apportionment. Signatures are not easy to obtain for PM. Classification typically exists in terms of elemental and organic carbon only: EC and OC. This distinction is too primitive for source apportionment. Soft X-ray techniques such as C 1s NEXAFS spectroscopy may be developed for the characterization and molecular speciation of carbonaceous PM, For example distinction between diesel exhaust and wood smoke is possible since there is an absence of graphitic structures in woodsmoke while graphitisation of diesel soot can strongly depend on engine operation conditions and fuel doping ^[1]. Another important environmental issue related to carbonaceous materials is their ability to absorb (often toxic) hydrophobic organic compounds (HOCs), such as PCBs (polychlorinated biphenyls) and PAHs (polycyclic aromatic hydrocarbons) in soils and sediments and its relationship with its chemical characteristics ^[2]. XPS, NEXAFS, FY-XAS and LY-XAS may all be used to explore the uptake of such compounds which is an essential pre-requisite for study of toxicology of such PM for example Cl L3-edge NEXAFS spectra have shown that there is a positive correlation between local chemical properties of carbonaceous PMs and their PCB sorption properties ^[3]. In many cases environmental samples are extracted under hydrous or wet conditions and typically need in situ characterisation methods. VERSOX’s ambient pressure end station will make it possible to conduct such studies in situ upon directly collected field samples. For example the interactions of soils and natural colloids under wet and hydrous conditions may be explored using VERSOX.

Aerosols

The role of atmospheric aerosols is one of the largest uncertainties in assessing the anthropogenic contributions to radiative forcing and climate change. Studies of chemical properties of the atmospheric aerosol is therefore central to ongoing climate research. Much of the aerosol is of a biogenic and other natural origin (e.g. sea spray) and is hydroscopic such that chemical and physical properties are rapidly changed upon uptake of water. Such phase changes in atmospheric aerosols have recently been recognized to be of key importance ^[4] but they are still very poorly understood. The atmospheric pressure end station of VERSOX will provide a unique facility for study of aerosol systems of atmospheric importance, in particular since it will allow investigations at pressures one order of magnitude above those accessible elsewhere. Specifically oxidation-induced changes in the viscosity and phase of a range of liquid and solid aerosols may be explored to improve the understanding of chemical and physical ageing processes of atmospheric aerosols. VERSOX may also be used in investigations of the behaviour of monomolecular organic layers covering such aerosols. XPS, NEXAFS, FY-XAS and LY-XAS may all be used to explore such phenomena. Furthermore the construction of a controlled humidity chamber to allow for experiments on solid-liquid/humid interfaces over the terrestrial atmosphere temperature range between -50° C and 50°C and the dev elopement of liquid and droplet jets will provide an ideal set up for experiments related to atmospheric chemistry.

Earth an planets

Planetary exploration missions are driving a need to better understand the local geology and atmospheres in comparison to terrestrial counterparts. The associated materials challenges are working with rare, small volume and spatially heterogeneous systems that require non-invasive and efficient probes. The new facility will, for example, help identify electron-hole recombination at defects in minerals and artificial materials using micro-imaging luminescence and XAS. Such experiments will provide the correlation between local chemistry and electronic structure of defects, revealing their origin and fluorescence mechanisms. This information is essential for improved environmental and personal dosimetry; it will also aid the analysis of the elemental abundances of planetary surfaces using X-ray techniques. Similar techniques will also be used to better understand charge recombination pathways in minerals from the Earth’s surface to improve Geological dating techniques – essential for better understanding past climate change, as well as human evolution and dispersal.

Interstellar space

Galactic gas exists in several phases, from hot collisionally ionised plasma to the dense, cold molecular clouds from which stars form. Numerous physical and chemical processes control the matter cycle of the Galaxy from interstellar gas to stars and back again to gas. Spectroscopy is a key tool in modern astronomy, revealing the Universe at a multitude of wavelengths. To understand what we see, we must complement our observations with laboratory studies. The capabilities of the VERSOX beamline will permit us unrivalled access across the soft X-ray spectrum for such laboratory studies providing a focus for laboratory studies that will help to unravel the details of astrochemistry and astrobiology, including the origins of life.

Chemistry plays a key role in the cycle of matter through the Universe ^[1]. Understanding the formation of molecules in the interstellar medium is a key question facing the astronomy and astrophysics communities. In the gas phase, the pathways from atoms and atomic ions to molecules and molecular ions are reasonably well mapped out ^[2,3]. However, simulations highlight a limitation of gas phase only models in that they fail to accurately predict the observed concentrations of many simple gaseous chemical species, including molecular hydrogen (H₂). Astronomers are now convinced therefore that the contribution from gas phase chemistry must be complemented by chemistry occurring on the surfaces of the dust grains that make up around 1% of the mass of a typical dense cloud ^[4,5]. Surface science has the potential to contribute significantly to our understanding of the gas-grain interaction ^[6] with experiments aimed at probing the formation of molecules such as H2, the desorption of icy grain mantles by heating and other energy sources, and the processing of icy mantles into pre-biotic materials. Although there is already much activity in astronomical gas-grain interaction, with UK-based groups often leading the way, key areas remain to be visited. The capabilities of the VERSOX beamline will allow us to address one of those areas and to open potential international dimensions associated with 4th generation light sources elsewhere in world to address others in this field.

Soft X-rays represent a minor but very important part of the interstellar radiation field. X-rays are much more penetrating into cold dense environments than radiation with ultraviolet and optical wavelengths. Hot, young stars are intense sources of such X-rays and are embedded in the remains of the protostellar disk from which the newly born star emerged. These disks are the building blocks of planetary systems retaining the icy grain population of the pre-stellar core and retain significant potential for chemical processing driven by the penetrating soft X-ray emission from the nascent star.

To understand what happens to an icy grain surface as it is irradiated with soft X-rays the combination of reflection-absorption infrared spectroscopy (RAIRS) and temperature programmed desorption (TPD) used by McCoustra and others ^[7] will be deployed to probe both physical and chemical changes in the surface. Such measurements complement and extend the work already being undertaken to investigate photon-driven chemistry on icy grains at longer wavelengths ^[8]. They will allow us to identify potential mechanisms driven by core excitations with the goal of ultimately developing pump-probe experiments utilizing fourth generation light sources such as FLASH and XFEL to investigate the energy flow subsequent to soft X-ray absorption. In particular this may allow us to investigate excitation transport in icy solids that is often cited as responsible for desorption in such systems ^[9].

The second issue that might ultimately be addressed by VERSOX is the origin of the primary asymmetry in biological molecules. All biological relevant amino acids are left handed while the sugars that form the energy source and constructional material in many biological systems are right handed. Already numerous experiments are showing us the photon- and low energy electron-induced processes in simple ice mixtures can result in the formation of pre-biotic molecules. But this chemistry is achiral – it does not introduce a handedness into the reaction products. Such experiments require coupling the output of VERSOX with additional external light sources including lasers. Additional enantiospecificity brought to enantiospecific desorption by enantiospecific gas phase photolysis could enhance the effectiveness of this mechanism for producing the primary asymmetry. But careful quantification of each of these mechanisms is urgently needed.