Environmental micro-reactor for atmospheric chemistry and physics

https://www.psi.ch/en/media/our-research/light-amplification-accelerates-chemical-reactions-in-aerosols

Organic particles can be highly viscous in air that is dry and cold. Therefore, it is important to quantify limitations of gases through organic materials as a function of temperature and relative humidity to better understand chemical and physical process involving atmospheric aerosol particles. Using state of the art spectro-microscopic techniques at the Swiss Light Source with the development of a new environmental micro-reactor, I investigate molecular diffusion of water vapor, ozone and other reactive gasses through organic particles less than 1 micrometer in diameter. At cold temperatures and low humidity, I expect that chemical reactions are limited to particle surfaces and microphysical processes such as ice nucleation and water condensation are altered.

Chemically mapping ice forming particles

https://www.psi.ch/en/luc/scientific-highlights/chemically-mapping-ice-…

https://cordis.europa.eu/project/id/701647

Precipitation is mostly formed via the ice phase in mixed phase clouds and ice clouds are very relevant for Earths’ climate. Ice nucleation is the first step in freezing. Freezing or prevention of freezing is common to everyday life, e.g. for food and drug storage, icing and de-icing, etc. However, the ice nucleation process is not well understood, since it occurs on the size scale of clusters of molecules and time scales of molecular fluctuations.

We built new instrumentation to observe when ice forms and use X-ray microscopy and spectroscopy to track the physical and chemical properties of ice nucleating particles with 35 nm spatial resolution. This is the first time ice nucleation has been measured in-situ in an X-ray microscope. The main technical challenge was temperature, and thus relative humidity control, while maintaining X-ray transparency. A sketch of our setup is shown. In a standard configuration, X-rays are focused through an aperture onto our sample. We have modified the aperture to also host a jet of nitrogen and control its temperature down to 170 K. The cold jet is directed to the back of an environmental cell mounted on a circuit board. Inside the cell with front and back windows (~100 nm thin), our sample is exposed to water vapour. The temperature of the sample is measured using a custom microfabricated sensor patterned using electron-beam lithography. Finally, the cold jet cools the sample only on the window exactly where we want ice nucleation to occur. An example of ice nucleation on iron containing nano-particles, ferrihydrite, in shown in the figure. This iron mineral is contained in mineral dust, which itself is assumed to be ice active. We can distinguish first, when water drops appear (blurred area), when ice first appears and grows, and measure the corresponding temperature and humidity.

This spot-cooling technique can be used for a wide range of applications and include, in part, determining ice nucleating properties of natural aerosol samples or observing chemical changes due to reaction in aerosol particles at low temperature. As a user instrument at the PolLux endstation of the SLS, this will be available to a variety of scientists in many disciplines.

This is what makes synthetic fuel go bad.

https://www.psi.ch/en/ene/synfuel

Reducing the amount of undesired products during synthetic fuel production is very important. To that end, I characterized the composition of particulate and soluble byproducts after the synthetic production of biocrude from hydrothermal processing. Hydrothermal gasification (HTG) and liquefaction (HTL) are technologies used to convert various biogenic feedstocks, such as microbial cultures, sewer sludge, black liquor and waste wood sawdust into sustainable gaseous and liquid fuels, respectively. These processes, which operate in or near supercritical water, rely on catalysts for selective fuel or gas production and heavily rely on the selective removal of unwanted carbonaceous particles or non-carbonaceous salts and compounds. The efficient recovery of brine (water and salts) is very important to protect any scavenger or catalyst that is used downstream, and relevant for recuperating costs by producing fertilizer. On the other end, understanding the formation and the fate of carbonaceous particles during such processes is of great importance to understand the impact of conditions, e.g. temperature, pressure, and time on the biocrude or the biogas production yield and composition. Indeed, the formation of carbonaceous deposits on the catalyst grains (macroscopic scale) and active sites (nanoscopic scale) is an important cause of deactivation, preventing long term operation and reducing biofuels/biogas yields and selectivity. I investigate particles and soluble compounds generated from HTL of spruce wood using scanning transmission X-ray microscopy coupled to near-edge X-ray absorption fine structure spectroscopy (STXM/NEXAFS). The desired product of HTL was the biocrude, which has great potential to be refined into liquid fuel and especially important for the aviation industry. The undesired solid particles and aqueous phase compounds contain organic carboxylic acids and unsaturated phenolic compounds. Catalysts are required for faster reactions forming targeted compounds in biocrude. I have investigated 2 mm grains that support nanometer size catalyst particles. There are carbonaceous deposits on the grain pores that can deactivate the catalysts over time, which can be quantified and avoided for better HTL performance. This would also benefit the production of aircraft fuels in next steps of fuel production since this fuel type requires nearly zero oxygen content.

Soot and oil nanoparticle emissions from aircraft engines

https://www.psi.ch/en/lac/projects/appropriate

Harmful gasses and aerosol particles are a health risk when inhaled. I quantify the concentration and composition of commercial aircraft engine emissions and identify their contribution to ambient air nearby Zurich airport and to ice cloud formation. Combustion in aircraft engines generate particulate matter (PM), which can induce oxidative stress in bronchial cells, as well as pulmonary and respiratory inflammation. This is especially the case for emission during idling and taxiing engine operation. At the engine exit plane, soot is the main particulate pollutant, like at any other combustion engine. However, lubrication oil is hypothesized here to be a significant fraction of emissions, and contains additives, such as tricresyl phosphates, and metals linked to neurotoxicity. My aim is to characterize particulate emissions directly from aircraft engines by chemically distinguishing between single or mixed soot and oil particles. Single particle analysis was performed using scanning transmission X-ray microscopy coupled with near-edge X-ray absorption fine structure spectroscopy (STXM/NEXAFS). Here, X-rays were used to resolve chemical detail on a scale of tens of nanometers. In collaboration with the Zurich University of Applied Sciences (ZHAW) Centre for Aviation, I sampled particles from in-service turbofans in the silencer of the engine Test Cell at SR Technics. Engines after previous repair and overhaul are tested for their performance in the Test Cell. The silencer part of the Test Cell is a large building designed to muffle sound and safely direct emissions away from the staff and surrounding work area. Particles sampled from the silencer were directed to either a multi-orifice uniform deposition impactor (MOUDI) or an electrostatic precipitator onto suitable substrates for further analysis. X-ray optical density, OD, images of particles emitted from an aircraft engine and their characteristic NEXAFS. Soot and oxygenated carbon functions that are more organic-like are present, highly characteristic of aircraft soot. This composition indicates quinone functionalities and non-soot like aliphatic carbon. Preliminary atomic resolution transmission electron microscopy results yield an amorphous coating on the soot similar to that found in our previous research. However, this composition is not typical of soot from other combustion and urban sources that typically have a spectral signature of carboxyl functionalities (COOH). I hypothesize that atmospheric processing and oxidation will generate carboxyl functions, and that fresh aircraft soot will be identified in the vicinity of the airport using this unique chemical marker at 287.5 eV during our upcoming field campaign.