My research interests focus on questions of the environment – the air that we breathe and the water we drink. In many parts of the world, including areas in the United States, air and water quality are serious issues with respect to public health and safety. Indeed, for example, the US Environmental Protection Agency has just recently changed its air quality standards to reflect the increased concern of very fine particulate material in the air that is transported over long distances via the prevailing winds. This fine particulate material (aerodynamic diameter < 2.5 micrometer or PM-2.5 for short) can easily be transported distances like ten thousand kilometers on the moving air masses. This makes control of these materials very difficult since the winds do not respect national boundaries and control can be a costly item.
In addition, these very fine particulates are not removed or exhaled during normal respiration in humans. Rather, these materials are trapped within the lungs and build up over time. This buildup can be deleterious to man. These scientific concerns very quickly become issues of public policy, economics, law and international agreements.
Working with others in the US and Europe, we have developed techniques to determine the elemental composition of these particulates in the atmosphere. We use commercial air sampling systems to collect samples of PM-2.5 and PM-10 material as well as TSP (Total Suspended Particulates) which is all particulate material with no size fractionation. The TSP material gives us information on the particulate material generated locally whereas the PM-2.5 and PM-10 material is indicative of material carried into the area via the prevailing wind patterns.
Our primary analytical method to determine the elemental make-up of these particulates is called Instrumental Neutron Activation Analysis (INAA). This is actually an old analytical technique dating back to Enrico Fermi and others. However, new and more sensitive detector technology coupled with computer-assisted data acquisition and analysis, has made this technique one of the most sensitive and quantitative elemental techniques available today. INAA techniques can readily determine elemental concentrations of approximately 55-60 of the naturally occurring elements to concentration levels of fractional parts per million and even parts per billion for some elements. INAA techniques are particularly valuable for investigating the heavier elements – aluminum and heavier.
In INAA, samples are subjected to neutron bombardment in a small research nuclear reactor. We use the facilities at the Massachusetts Institute of Technology for this neutron irradiation. This neutron bombardment makes the samples slightly radioactive. We then analyze the resultant radioactive decay patterns or spectrum of the emitted gamma radiation. These gamma emission patterns, which are different for each element, can be used to uniquely identify the elemental makeup of the sample. The gamma emission pattern identifies the element; the number of emitted gamma rays indicates the amount of the element in the sample.
Other analytical procedures available for this research include x-ray fluorescence (XRF) and energy dispersive x-ray analysis (EDX). Both of these techniques use emitted x-rays as the identifying signature of the elements and are most useful for investigations of the lighter elements – e.g. Si, O and Cl. Finally, we have available a scanning electron microscope (SEM) which can be used to view the size and surface morphology of the particulates. Smooth, rather rounded particles are most often ordinary soil particles like sand. Irregular, fractured particles are most often associated with combustion by-products. EDX of individual particles will give us additional information as to the elemental makeup of these specific particles.
With information on the elemental concentration of numerous air samples collected over a period of time, the analysis next involves the use of advanced statistical techniques to determine the individual sources and relative source contributions of these materials. Analysis of variance (ANOVA) techniques are used to help identify individual sources. Back wind trajectory analyses, developed by NOAA, allow us to determine where a particular air mass that we sampled today came from one, two, three days previously. Our overall goal is to identify sources of particulate materials and to quantify their relative contributions.
Our current research focuses on heavy metals in the atmosphere – materials such as mercury (Hg), cadmium (Cd) and arsenic (As). Mercury in the atmosphere is a particular concern in some parts of the world since it occurs naturally due to the weathering of exposed granite. In addition, Hg is thought to be emitted into the atmosphere during the combustion process of fossil fuels particularly coal. Our group at Fairfield is currently collaborating with others in Budapest, Hungary and Istanbul, Turkey and at MIT in an investigation of sources of Hg emissions in Central and Eastern Europe.
