Most environmental processes occur at the interface between different phases of matter present in natural systems. Hence, it is crucial to study the chemistry at the interface of materials in these systems at the molecular level and under environmentally-representative conditions. My research in environmental surface chemistry tackles important and unresolved scientific problems in geochemistry and atmospheric chemistry. We utilize state-of-the-art equipment and computational software to study processes at the gas/solid and liquid/solid interfaces. Below is detailed description of the ongoing research programs in my lab at Laurier:
1- Projects in Atmospheric Chemistry:
The lower atmosphere, known as the troposphere, comprises a large concentration of minute airborne particles known as aerosols. Aerosols in the troposphere have complex chemical composition and they impact our lives in a number of ways. Reduced visibility seen on hazy days and respiratory health problems are just two examples of aerosols impact on a regional scale. On a global scale, aerosols contribute to climate change as they influence the amount of sunlight reaching the Earth’s surface, alter properties of clouds, and provide media for chemical reactions in the atmosphere. Computer simulations of the climate give us the capability of quantifying the magnitude of aerosols contribution to climate change. Yet aerosols representation in these simulations is still inadequate mainly because aerosols are complicated in nature and their reactivity and properties change with time while suspended in air. Thus, it is imperative to address scientific questions related to aerosols through experimental studies to better our understanding of the aerosols impact on our climate system.
Organic matter on aerosols originates from pollution stemming from human activity, natural sources (emissions from trees and animals), and biomass burning. Since reactions occur mainly on aerosols surfaces, and in order to simplify the complex chemical nature of aerosols, we prepare and characterize model surfaces composed of the most abundant chemical compounds identified in real aerosol particles. We also study the processing and aging of aerosols caused mainly by reactions with pollutant gases found in the atmosphere. We use experimental techniques that allow monitoring reactions on surfaces under controlled environments such as Fourier transform infrared spectroscopy. Results obtained from these studies will increase our understanding of the aging process of aerosols and their overall impact on the global climate.
2- Projects in Interfacial Geochemistry:
Arsenic and its compounds are listed on the pollutant priority lists of the Canadian Environmental Protection Act (CEPA) and the U.S. EPA. These compounds are stable in geochemical environments and identified to pose adverse health effects to humans, including cancer. The current Canadian interim maximum acceptable limit of total arsenic in drinking water is 25 micrograms per liter (parts per billion), while that of the U.S. EPA is 10 ppb.
Arsenic in the environment exists in two forms: inorganic and organic. Contamination of water bodies (rivers, steams, groundwater) with inorganic arsenic originates from the weathering of arsenic-containing ores and minerals and results in releasing arsenic into water. Other sources also include tailings of abandoned and recent gold mining operations, and wood preservative facilities. Inorganic arsenic compounds are known for their high toxicity, and water contamination with this form of arsenic is widespread in different parts around the world and in north America including Canada’s east coast and northwestern territories.
In addition, the organic form of arsenic is found in the environment as a result of microbial activity and also introduced to the environment through their historical use as herbicides and through the disposal and land application of contaminated poultry litter as some organic arsenic compounds are used as feed additives in the poultry industry.
Our work in this area is motivated by the fact that potential transformation of organic arsenic to inorganic arsenic in water and soil pose an environmental risk. However, the fate of organic arsenic in soils and natural waters depends to a large extend on how these compounds interact with soil particles and organic matter derived from the decomposition of plants. These interactions also affect the rate at which organic arsenic gets transported from one location to another, and the rate at which these compounds become available to plants and other organisms. Our work aims at quantifying the strength of interactions between organic arsenic compounds with model soil components using infrared spectroscopy. I am currently collaborating with Professor Ian Hamilton in the Chemistry Department at Laurier in running computational chemistry projects on systems related to our ongoing research program in geochemistry. Specifically, surface complexes of organoarsenical compounds are modeled using theoretical methods to gain further insight into their geometries and to aid in the interpretation of the experimental infrared spectra of interfacial species. Relative Gibbs free energies for ligand exchange reactions at the water/solid interface will also be calculated.
The results we are looking to obtain from our studies will be used to feed pollutant-transport models used predict how far can a pollutant plume travel in the water supply and how long would it take to reach water distribution facilities. The outcome of these transport models would be used to help municipalities decide on the implementation of pollutants-removal technologies from contaminated waters.
We are grateful for the funding provided by: