Research Interests

Atmospheric chemistry, in general, might be boiled down to two main areas:

1) Processes: What are the sources and sinks (production and loss rates) for gases and particles in the atmosphere?

2) Impacts: How does atmospheric composition affect air quality, climate, crops, etc.?

Humans alter the atmosphere (think ozone hole, acid rain, smog, climate change), and these questions are directly relevant to the health of the Earth and every living thing on it. Much of my research focuses on the interactions between natural and human emissions.

Surface-Atmosphere Exchange (Fluxes)

Think of the atmosphere as a leaky bathtub with the faucet on. We care about how much water is in the tub right now, but we also want to predict how it will change (because we are nerds). To do this, we can't just measure the volume of water in the tub; we have to know the rates of input and output. Measuring the amount of trace gases in the atmosphere is not easy, but we have ample experience doing it. Quantifying the inputs and outputs, or sources and sinks, is much tougher.

Using a special technique called eddy covariance, it is possible to directly measure the exchange, or flux, of trace gases between the atmosphere and Earth's surface. The cartoon to the left summarizes a case study of fluxes measured over a forest using the NASA DC-8 (Wolfe et al., GRL 2015). Red text denotes process parameters that we were able to directly quantify using flux observations combined with a fairly extensive payload. Such measurements allow us to test emission inventories and model algorithms in a way that is far more powerful and direct than the traditional method of just measuring gas concentrations.

My current research includes applying this technique to measure fluxes of both reactive (VOC, NOx, ozone) and greenhouse (CO2, CH4) fluxes.

Processes affecting composition in the lower atmosphere. Red text indicated processes that can be quantified with airborne eddy covariance.

Hydrocarbon Oxidation

The atmosphere is very efficient at cleaning itself. When a hydrocarbon (e.g. gasoline vapors, forest emissions, wildfire smoke) enters the atmosphere, it is rapidly removed by a handful of reactive molecules. As the poor hydrocarbon gets chewed up, smaller molecules are formed, like formaldehyde (HCHO). As part of my research at NASA, I collect and use airborne observations of HCHO to help us understand these oxidation processes, which are also strongly influenced by human emissions. My research also enables better utilization of satellite-based measurements to study global processes.

Formaldehyde as measured from NASA's satellite-based Ozone Monitoring Instrument (OMI) in August 2006. Yellows and reds indicate high HCHO in regions with lots of trees. Globally, vegetation is the strongest source of hydrocarbons.

Instrument Development

Many important chemical species in the atmosphere are challenging to measure, partly because their concentrations are low (1 molecule of interesting stuff per million/billion/trillion molecules of air). This problem is compounded by harsh environmental conditions in the field - research airplanes are prone to vibrations, rapid temperature swings and pressure changes. At the NASA Goddard In Situ Observations Laboratory, I work with other scientists and engineers to develop airworthy instrumentation to measure a range of greenhouse and reactive gases. We deploy these instruments on airborne platforms while participating in multi-institutional collaborative research efforts.

Payload deployed on the NASA C-23 Sherpa aircraft to measure CH4, CO2, N2O, CO, H2O, and HCHO.

Numerical Modeling Tools

Computer simulations allow us to both evaluate our current understanding of atmospheric processes and identify new avenues of research. In the course of analyzing field and laboratory data, I have developed both 0-D (single box) and 1-D (column) models that can be applied to a range of problems. In particular, the 0-D model is designed to be user friendly and highly flexible, as this type of modeling is integral to nearly all atmospheric chemistry studies. A major goal of this work is to develop community tools, thereby providing a common platform for synthesizing scientific findings. The 0-D model is so cool that it has its own page.