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 brief description of these bulleted topics are provided below.

Heterogeneous atmospheric chemistry of mineral dust and its components - carbonates, clays and oxides. It has become increasingly clear that all kinds of particles - including ice, sea salt and mineral dust - are present in the Earth's atmosphere and that the surfaces of these particles play a role in the chemistry of the atmosphere. The ozone hole is one example of how heterogeneous chemistry involving chlorine-reservoir species on ice particles can decrease ozone levels in the stratosphere. In the troposphere, the region closest to the Earth's surface, there are many more particles and the heterogeneous chemistry of these particles with trace gases such as NO₂, HNO₃, SO₂, O₃ and organics is not well understood. Heterogeneous reactions that take place on mineral dust in the troposphere may provide the "missing link" for some reaction schemes that cannot be explained solely by gas-phase reactions. In the Grassian research group, we are using a combination of surface spectroscopy, microscopy and particle analysis to gain an understanding of kinetics and mechanisms involved in these important reactions. Reaction rate data measured in our laboratory for heterogeneous reactions of trace gases with mineral dust and its components (CaCO3, α-Fe₂O₃, aluminum silicates.) are currently being incorporated into global chemistry models.

Surface science of environmental interfaces. The research described here falls into the broad area of environmental molecular surface science. The chemistry of single crystal surfaces of CaCO₃, MgO and BaO with several pollutant molecules including NO₂, HNO₃ and SO₂ at the gas-solid interface as a function of relative humidity is being investigated. Nitrogen and sulfur oxides represent major components of air pollution and there is a great deal of interest in these gases from several perspectives including the heterogeneous chemistry of these gases with aerosol particles in the atmosphere (e.g. mineral dust aerosol) and the environmental remediation of these gases from automotive exhaust and power plants. Our goal is to determine fundamental molecular-level aspects of the chemistry of nitrogen and sulfur oxides on the surface of oxides and carbonates under ambient conditions. It is well documented from a number of studies using a wide range of surface sensitive techniques that single crystal oxide and carbonate surfaces cleaved in air undergo facile reaction with atmospheric H₂O to yield hydroxyl and bicarbonate, in the case of carbonates, groups on the surface. Water readily adsorb to these surfaces, most likely through hydrogen bonding to the surface OH and CO₃H groups. It is our goal to understand the molecular level details of these reactions by using a combination of spectroscopy and Atomic Force Microscopy (AFM) to study these "wet" complex interfaces. This combined approach will give us important information about the molecular-level mechanistic aspects of these reactions including surface speciation, surface segregation and phase transitions.

A combined approach of spectroscopy and microscopy to study surface reactions under ambient conditions and pressure will provide a detail understanding of these reactions.	Schematic cartoon of the complexities of an environmental interface. Oxide and carbonate surfaces under ambient conditions of temperature and relative humidity. Surfaces of oxides and carbonates are usually terminated with hydroxyl groups and bicarbonate that can readily adsorb water.

Mineral dust and its impact on global process including climate and ocean biogeochemical cycles- the role of chemistry. Mineral dust aerosol is largely composed of soil particles lifted into the atmosphere by wind action. The flux of mineral dust into the troposphere varies greatly with location and season, but it is estimated that average annual emissions of mineral dust into the atmosphere total ~1000-3000 Tg/yr with the Saharan Desert being the largest global contributor. The frequency and intensity of dust events, and ultimately the mineral aerosol loading in the atmosphere, are expected to continue to increase as long as improper land-use practices are driven by economic, social and political circumstances. By the year 2100, mineral aerosol production is anticipated to increase by 10% from its current level [IPCC Climate Change, 2001]. Mineral dust aerosol plays an important role in the coupled global processes of chemistry, climate, biogeochemical cycles, and health. In our laboratory, we are trying to better understand how mineral dust can impact climate and biogeochemical cycles as described below.

Environmental remediation and CWA decontamination with nanocrystalline zeolites. Nanoscience and nanotechnology have potential use in environmental applications. In collaboration with Professor Sarah Larsen (chemistry), we are investigating nanocrystalline zeolite materials as new adsorbents and catalysts for use in environmental remediation, environmentally benign synthesis and the decontamination of chemical warfare agents. Zeolites are crystalline, aluminosilicate molecular sieves with pores of molecular dimensions. Zeolites can be synthesized with a wide range of pore sizes and topologies and are used in applications such as catalysis and chemical separations. The zeolite chemical composition, framework topology and pore size can be varied to control selectivity and reactivity. Nanocrystalline zeolites are zeolites with particle sizes less than 100 nm. These materials may be particularly useful in environmental applications due to the small crystal sizes and large internal and external surface areas. We are currently focused on using nanocrystalline zeolites in the decontamination of chemical warfare agents (CWAs). Finding new methods for CWA decontamination is a high national priority. Current research shows that nanocrystalline zeolites may be promising for this application. In the case of the environmental remediation of NOx, nanocrystalline zeolites have been shown to be more effective in the selective catalytic reduction (SCR) of NOx with urea.

Nanoparticle Fe as a reactive constituent in air water and soil. The goal of the proposed work is to understand the reactivity of iron (Fe) oxide nanoparticles in air, water, and soil environments. Fe oxide particles in the nanometer size range (< 100 nm) are ubiquitous in nature and their occurrence ranges from ultra-fine mineral dust in the atmosphere to nanocrystalline precipitates in the hydrosphere. The remarkable reactivity of Fe oxides has led to intense interest in the origin and reactivity of nanoparticle Fe oxides in natural environments as it is also hypothesize that unique reaction mechanisms occur at the surface of Fe oxide nanoparticles that do not extrapolate outside of the nanoscale domain. This is a new project that is being done in collaboration with Professor Michelle Scherer (Environmental Engineering).

Impacts of manufactured nanomaterials on human health and the environment. Another aspect of our work involves the implications of nanoscience and nanotechnology and the environmental consequences of nanomaterials. In particular, we are collaborating with colleagues in Public Health (Professors O'Shaughnessy and Thorne) to better understand the potential health effects of manufactured nanomaterials should they become suspended in air. The potential effects of manufactured nanomaterial aerosol on human health are being investigated and will be compared to ultrafine carbonaceous particles typically found in the environment from combustion processes. It is expected that these studies will help answer questions as to the potential impact of manufactured nanomaterial aerosol on human health as there is clearly a lack of information in this regard. Two important factors of the proposed activities are the comparison of the potential health effects of manufactured nanomaterials to other anthropogenic sources of ultrafine particles from combustion processes and the effect of surface coatings, on the toxicity of these particles.

Along with our colleagues in Public Health (Professors O'Shaughnessy, Peters and Heitbrink) we are also trying to identify and evaluate methods to measure airborne nanoparticle concentrations, characterize nanoparticles and determine the collection efficiency of commonly used respirator filters when challenged with nanoparticles. These studies will assist with assessment methods for nanoparticles in the workplace.