Biosphere - Atmosphere Interactions
Welcome to Team Plant!
We aim to understand how plants affect atmospheric composition in both outdoor and indoor environments. Outdoors, forests act as a large source of VOCs that contribute to air pollution (in terms of ozone and aerosol formation) and affect climate. Therefore, we're trying to quantify its sources and sinks so that models can better predict atmospheric composition. Indoors, where we spend 90% of our time, the extent to which plants act as sources and sinks of VOCs is poorly understood. As a result, we're trying to constrain these processes to assess their impact on indoor air composition and human health.
Current Outdoor Plant Research
(1) Motivated by field studies using our formaldehyde (HCHO) FILIF instrument in forests located in Michigan, Colorado, and California, as well as the Amazon rainforest, we recently wrapped up experiments that studied the bidirectional exchange of HCHO with red oak (Quercus rubra) and Cypress saplings.
(2) Inspired by previous work that showed the conversion of 1,2-ISOPOOH (isoprene hydroxy hydroperoxide) to methyl vinyl ketone (MVK) and HCHO on heated metal surfaces inside instruments, we are currently exploring the extent to which 1,2-ISOPOOH decomposes on leaf surfaces to HCHO and MVK. This work utilizes our group's PTR3 mass spectrometric instrument in NH₄⁺ mode.
The schematic above summarizes the HCHO and ISOPOOH experiments in our lab. The main goal is to quantify these processes for incorporation into atmospheric chemistry models on the local, regional, and global scales to predict atmospheric composition.
Examination of the Surface Reactions of Organic Hydroperoxides and their Effect on Model-Observational Disagreement
Senior Thesis Project
Understanding the differences between chamber studies and laboratory studies is crucial for relating laboratory data to the real world. Laboratory and field studies of multifunctional hydroperoxides and their oxidation products in high NOx (urban) and low NOx (pristine) environments are relevant because urban oxidation products of ISOPOOH like Methyl Vinyl Ketone (MVK) and Methacrolein (MACR) are significantly more volatile than ISOPOOH or the pristine oxidation products such as Isoprene Epoxydiols (IEPOX) (Bernhammer et al., 2017). Additionally, these processes affect atmospheric OH reactivity and the formation of ozone (Kaiser et al., 2016). The differences between urban and pristine processes for the oxidation of multifunctional organic hydroperoxides demonstrate the importance of understanding exactly how ambient NOx concentrations affect these mechanisms. Chamber studies on the oxidation of ISOPOOH reveal that in humid conditions there is a catalytic conversion of two ISOPOOH isomers into MVK and MACR on the stainless-steel surfaces of chambers (Bernhammer et al., 2017). This conversion of ISOPOOH into two urban oxidation products could greatly influence models which attempt to predict the yields of urban and pristine products at observed NOx levels. Analyzing the conversion of ISOPOOH to urban oxidation products and adjusting models to account for this conversion in chamber and field studies will greatly improve their accuracy.
This project used the Framework for 0-D Atmospheric Modeling (F0AM) to estimate the effect of photochemical surface reactions, such as the conversion of pristine ISOPOOH oxidation products, and adjusted models to better predict concentrations of organic hydroperoxides and their oxidation products. Previously performed chamber and field studies provided the data being used to evaluate these atmospheric models. Models for the southeastern United States were adjusted first, and these adjustments were also applied to data sets from forests in the Amazon and western United States to evaluate the importance of these surface processes in different conditions.
Undergraduate Researcher: Greg Valtierra ('21)
Graduate Student Advisor: Jack Hensley
Faculty Advisor: Professor Frank Keutsch