Research Interests

Professor Grassian’s current research interests include:

Heterogeneous Chemistry of Particles in the Atmosphere with Trace Gases: From Fundamental Molecular Surface Processes to Global Impacts

• heterogeneous atmospheric chemistry of mineral dust and its components - carbonates, clays and oxides
• surface science of environmental interfaces
• mineral dust and its impact on global process including climate and ocean biogeochemical cycles - the role of chemistry

and Applications and Implications of Nanoscience and Nanotechnology in Environmental Processes

• environmental remediation and CWA decontamination with nanocrystalline zeolites
• nanoparticle Fe as a reactive constituent in air water and soil
• impacts of manufactured nanomaterials on human health and the environment

A variety of research tools and state-of-the-art instrumentation are used to in these studies. These instruments include

• Knudsen cell reactor
• ATR-FTIR flow reactor
• Aerosol flow reactor with FTIR analysis, SMPS, APS and CCN counter
• Environmental aerosol chamber
• Surface analysis - XPS, UPS and AES
• Microscopy – SEM, TEM and AFM
• Transmission FTIR

Some of these instruments are described in more detail below.

Knudsen cell reactor. Knudsen cell measurements can be used to determine reaction probabilities of gases on solid surfaces under dry conditions. These kinetic measurements are needed in order to quantify heterogeneous atmospheric processes for input in global atmospheric models. The flow of gas through a cell at low pressures is measured in the presence and absence of a reactive surface, in our experiments we are interested in the uptake of gases on components of mineral dust aerosol. The particles (e.g. CaCO₃, α-Fe₂O₃, kaolinite…) are placed inside of a sample holder. A plunger with a cover at end is used to isolate the metal oxide particles from the gas. The flow of gas through the cell is monitored with a UTI-Detector II quadrupole mass spectrometer (QMS). Initially, the cover is in place so that the reactive particles are not exposed. After a steady-state flow is established through the low pressure cell, the cover is lifted up to expose the metal oxide particles. The design of the Knudsen cell is such that the volume of the cell stays constant when the metal oxide particles are exposed. Therefore, no volume corrections need to be made and the reaction probability, gamma. A diagram of our multi-sample holder Knudsen cell reactor is shown below.

ATR-FTIR flow cell reactor. A recently designed Attenuated Total Reflection (ATR)-FTIR flow cell reactor is used to measure the infrared spectrum of molecules adsorbed on carbonate, oxide and clay powders. The reactor is particularly well-suited to measure reaction kinetics as a function of relative humidity. Experiments done to investigate the uptake of organic acids on carbonate surfaces recently demonstrated the utility of this flow reactor. A commercial ATR horizontal liquid cell apparatus (Pike Technology) was modified for these experiments (see schematic).

Data collected for formic acid uptake on CaCO₃ at 33% RH are shown below.

Aerosol flow reactor with FTIR analysis, SMPS, APS and CCN counter. A new multi-analysis aerosol flow reactor has been designed for laboratory studies of atmospheric aerosol and their impact on climate. The aerosol flow reactor can employ three different aerosol generators – a nebulizer, an electrospray atomizer, and a fluidized bed generator. The aerosol flow reactor is being implemented in several different ways. The instrument can be used to

1. measure the optical constants of the components of mineral dust aerosol by simultaneously measuring particle size distributions using both the SMPS (scanning mobility particle sizer) and APS (aerodynamic particle sizer) and the FTIR extinction spectrum of these particles. These sizing instruments allow us to measure the full range of particle sizes from 10 nm to 20 microns.
2. measure the ability of mineral dust particles to nucleate clouds. In these experiments the aerosol flow is directed to a CCN counter where the supersaturation ratio can be measured.
3. measure hygroscopic response of size-selected aerosol particles. For particles that undergo a phase transition from solid to liquid (deliquescence), the deliquescence relative humidity can be accurately determined. The particles are size selected by first being sent through the differential mobility analyze labeled DMA 1 in the schematic below.

Surface Analysis - XPS, UPS and AES. Through the NSF major research instrumentation program, we have recently purchased a state-of-the-art surface analysis chamber for X-ray Photoelectron Spectroscopy (XPS), Ultraviolet Photoelectron Spectroscopy (UPS) and Auger Electron Spectroscopy (AES). The instrument is capable of The instrument is capable of

• XPS small area analysis (˜10micrometers)
• two-dimensional elemental XPS and AES mapping
• two-dimensional chemical state mapping
• charge neutralization for the analysis of insulating samples
• depth profiling
• automated analysis of hundreds of samples or hundreds of different areas of the same samples
• wide spot size UPS

The instrument has just been recently installed and high quality data are being collected. The instrument is being used in several of our research projects. Jonas Baltrusaitis stands next to the newly delivered Krato’s Ultra Axis surface analysis chamber. This instrument is designed for XPS.

SEM/EDX images

Heterogeneous reactions of individual particles from an authentic dust sample – China Loess – followed by SEM/EDX. The three particles labeled a, b and c are a clay particle, calcium carbonate particle and quartz particle. These show different reactivity with nitric acid (e.g. CaCO3 particles shows unique morphology changes due to the formation of deliquescent calcium nitrate), demonstrating the difference in reactivity of the components of mineral dust aerosol. These studies are being done with Dr. Alexander Laskin at Pacific Northwest National Laboratory.

TEM images

TEM image of 5 nm particles used to investigate the health implications of commercial manufactured nanoparticles. The individual particles can be seen in this image. The scale bar on the bottom is 20 nm.

AFM images

AFM Height images of MgO(100) (a) before and (b) after reaction with nitric acid. The white spots in image (b)are magnesium nitrate crystallite, not a continuous thin film that was proposed from spectroscopic studies. These crystallites are on the order of 0.5 to 1 micron wide and ˜40 nm in height.

Transmission FTIR. A transmission FTIR cell is currently being used to study the adsorption of gases on oxide, clay and zeolite powders in the different research projects that are ongoing in the Grassian laboratory. There are several different designs of the cell that we use. One can be used to heat and samples. The temperature range is from 100 to 900 K. The transmission FTIR cell can also be used in photocatalysis studies.