Participating Faculty

I am currently investigating the mechanisms underlying heterogeneous nucleation of ice in the atmosphere. Ice forms through two paths in the atmosphere. In the upper troposphere and stratosphere, where temperatures can be colder than 40 degrees below zero, ice can form through homgeneous nucleation of supercooled water droplets. However, in the lower troposphere, ice forms with the aid of small bits of insoluble dust - hence the name heterogeneous nucleation.
One approach is to probe the arrangement of water molecules on suitable substrates (e.g. muscovite mica or long chain alcohols) with Fourier Transform Infrared Spectroscopy. Since the hydrogen bonding network between water molecules is particularly sensitive to perturbations from the influence of the substrate, I can relate the spectroscopic signature to the water-substrate bond strength and to the degree of order in the film of water molecules coating the substrate.

My current research focus is the application of remote sensing data to studies of volcanic degassing, volcanic eruption clouds, and anthropogenic pollution. Space-borne sensors such as the Ozone Monitoring Instrument (OMI) on NASA’s Aura satellite now allow us to probe the chemistry of the lower troposphere and measure the abundance of sulfur dioxide (SO2), ozone, bromine monoxide (BrO), nitrogen dioxide (NO2) and other important trace gases with unprecedented sensitivity. The cross-platform sensor synergy provided by NASA’s A-Train satellite constellation is advancing our knowledge of volcanic cloud composition and transport. My main focus is SO2, a precursor of sulfate aerosol, which plays an important role in the atmosphere through negative climate forcing and impacts on cloud microphysics. The spatiotemporal variability of natural and anthropogenic SO2 emissions, and hence of global sulfate aerosol abundance, is poorly constrained, impacting the accuracy of climate models.

Atmosphere-surface exchange of climate-forcing gases (e.g., CO2, CH4, N2O) and aerosol precursors (e.g., terpenes, NH3) is affected by changes in land use and biodiversity, climatic perturbations, and atmospheric deposition of macronutrients (e.g., C, N, S, P) and plant stressors like ozone. The goal of our research is (1) to advance mechanistic understanding of the biogeochemical processing of synthetic organic chemicals, climate-forcing gases, and aerosol precursors and (2) to improve the ability of multimedia environmental and Earth system models to predict the fate of chemicals in various compartments of the environment and responses of the Earth system to nutrient supply, biospheric stressors, changes in land use and biodiversity, and climatic perturbations. Research activities include sampling and analytic technique development, landscape- and regional-scale measurements of ambient levels and atmosphere-surface exchange rates from surface- and aircraft-based platforms, and development of parameterizations for environmental and biogeochemical processes.

We are interested in elucidating the effects that aerosols of both anthropogenic and natural origin, have on earth's climate and air quality. The goal of our research is to contribute to a better fundamental understanding of aerosols and to provide tools and knowledge to advance future climate models' performance and improve air quality. The effects of aerosols on the climate system -- through the direct, semidirect and indirect effects and through deposition on snow and ice -- are still poorly quantified and constitute one of the largest and most challenging uncertainties in climate science. This dramatically reduces our ability to correctly describe the radiative balance of our planet and to produce accurate and credible predictions for future global changes. The difficulty in correctly representing aerosols in climate models is related to the extreme complexity of the aerosol properties and their interactions with the environment. We focus our research efforts on studying aerosol optical properties and their interaction with solar radiation, clouds and snow by analyzing data collected by means of in-situ measurements performed in different locations of the globe (from polluted urban areas to remote regions) on board aircraft or on the ground. We also study aerosol morphology and the relation of morphology to optical properties.

My current research interests in atmospheric science are in organic pollution and impacts on ecosystems. My research group has developed technologies to speciate and measure concentrations of organic chemicals in indoor air and urban, rural, and remote outdoor air. This technology is used in micrometeorological approaches to measure air-surface exchange rates. We have applied the technology to carry out over-water measurement of air-water gas transfer of semivolatile organic pollutants and carbon dioxide in the Laurentian Great Lakes. We have also developed a mechanistic two-dimensional Lagrangian model to quantify the effects of boundary layer meteorology on transport and transfer of scalars in coastal regions, which we employ to improve estimates of pollutant loading, to determine optimal sampling schemes, and to compare with measurements.

My atmospheric science research focuses on the vertical exchange of matter and energy between forests and the atmosphere. I am interested in how management (e.g. timber harvesting, peatland draining), invasive species and climate change will alter ecosystem processes. I employ techniques that monitor the exchange of water and carbon from individual plants (e.g. sapflow, leaf-gas exchange) to whole ecosystems (e.g. Bowen ratio and eddy covariance techniques).

I have been studying volcanic gases and particles for 40 years. I use direct sampling methods and a wide variety of remote sensing, including ground-based and satellite methods. A recent focus has been the fate and transport of volcanic ash, which is interdisciplinary science involving meteorology, volcanology and atmospheric physics and chemistry. Environmental effects of explosive eruptions, including effects on human health and aircraft safety are also addressed in my work.

My research group is working on problems related to the physics of clouds in the earth's atmosphere. For example, have you ever noticed while flying that the ride gets bumpy when the airplane enters a cloud? It's because clouds are turbulent and we are interested to learn whether the turbulence in clouds can accelerate the formation of raindrops. We study this and related problems in many ways, ranging from computer simulations to laboratory experiments, to field studies. In the lab we have built a turbulent "cloud in a box" and we use digital holography to see first hand how cloud droplets get jostled around during their own turbulent flights. Together with our close colleagues at the Institute for Tropospheric Research in Leipzig, Germany, we take our own bumpy flights through clouds, making measurements that help link our idealized laboratory work to the real world. When we're not busy with turbulent clouds, we think about how ice forms in clouds --- laboratory experiments here at Michigan Tech and with colleagues in Leipzig using the Leipzig Aerosol-Cloud Interaction System are teaching us about the mysteries of how dust, volcanic ash, and other materials act to catalyze the formation of ice crystals.

Human activities (such as the intensive use of fossil fuel, urbanization, deforestation, agricultural expansion or intensification) have been imposing significant perturbations to the atmosphere. I am interested in a wide range of research topics in global environmental change, especially the interactions among climate, atmospheric chemistry, ozone and aerosol air quality, land use/land cover and biosphere-atmosphere exchange.

Interests: atmosphere-biosphere interactions, impacts of atmospheric deposition and climate variability on ecosystems.

Forestry