Participating Students - Robert Hansen

Robert Hansen
Indiana, University
Department of Chemistry
Enrollment Year 2009
Email: rfhansen at
Atmospheric Mentor: Phil Stevens
Biospheric Mentor: Rich Philips

Robert Hansen graduated from Baldwin-Wallace College in 2006 with a B.S. in chemistry. Currently, he is a Ph. D. student in chemistry at Indiana University, conducting atmospheric chemistry research in the laboratory of Dr. Philip Stevens.  Rob was awarded a BART summer-only fellowship in the summer of 2008; it was this fellowship that introduced him to the BART program.

Rob’s research focuses on measurement of total hydroxyl radical (OH) reactivity in various regimes within forested environments. As part of this research, he has developed and tested an instrument for measuring total OH reactivity, which has been deployed in the 2008 Nucleation in ForesT environments (NIFTy) campaign in southern Indiana and the 2008 PROPHET campaign at UMBS.

Volatile organic compounds from biological sources (BVOCs) have been shown to influence tropospheric chemistry on both local and regional scales. Although there has been significant progress in recent years, our understanding of the impact of BVOCs on tropospheric chemistry within forested environments is still not complete and there may be many BVOCs that have not been identified. Furthermore, emissions of BVOCs from soil and plant litter and their impact on tropospheric chemistry within forested environments has not been investigated extensively; these emissions could contribute more to subcanopy tropospheric chemistry than previously thought. Furthermore, the composition of BVOC emissions from soils and plant litter from a specific area can depend on soil temperature, nutrient availability, and soil moisture, as microbes in the soil and litter layer produce BVOCs through metabolism of compounds in plant litter and BVOC emissions from below ground plant tissues. The composition of BVOC emissions from soils and plant litter in a specific area also depends on tree speciation, as storage of volatile organic compounds (VOCs) within plant appendages and production of BVOCs varies among tree species. It is important to understand how BVOC emissions affect tropospheric chemistry with the possibility of changes in forest speciation from global climate change. One method that has been used to investigate the chemistry of BVOCs is total hydroxyl radical reactivity, which focuses on the reaction of the hydroxyl radical (OH) with trace species in ambient air. The difference between the measured total OH reactivity and that calculated from collocated measurements can give some information about the reactivity and quantity of unknown BVOCs. The difference in reactivity values can also be plotted as a function of temperature to examine the temperature dependence of emission of the unknown BVOCs. Measurements of total OH reactivity will be made with a turbulent-flow system above the forest canopy, within the forest canopy, and near ground level; these measurements will be combined with collocated measurements of VOC concentrations and analysis of the litter and soil composition to investigate the impact of BVOC emissions on tropospheric chemistry both above and below the forest canopy.