Hydrogen Production
Methane pyrolysis is potentially low-cost method of hydrogen and carbon black production which generates little to no greenhouse gas emissions. Our research focuses on methane pyrolysis and low-cost catalyst. A video describing some of our work is found below.




Aerosols

Aerosols cause ~4 million premature deaths per year (World Health Organization, 2013) and are one of the largest contributors to climate forcing (UN Intergovernmental Panel on Climate Change, 2014). A reduction in the negative effects of aerosols is not possible without instruments to quantify particle emissions and understand their properties. My most significant contributions have been inventing and developing aerosol instruments and using them to determine important particle properties:

Aerodynamic aerosol classifier
A current focus of my research is the development of an instrument, called the aerodynamic aerosol classifier (AAC), which classifies nanoparticles by their aerodynamic size. Particle classifiers are used to separate polydisperse aerosols into classes (or into a monodisperse aerosol) so that the particles can be counted, weighed, or measured by another instrument. The differential mobility analyzer (DMA) has been the ubiquitous choice for nanoparticle classification for decades. However, the interpretation of DMA data requires knowledge (or assumption) of the electrical charge state of the particles. This can often lead to ambiguity (or error) in the interpretation of the results or requires the use of charge-correction schemes.

The AAC is an instrument which classifies particles by their aerodynamic diameter. It avoids any dependence on electrical charge by using a centripetal force for particle classification. This instrument could be used to measure nanoparticle size distributions (when combined with a particle counter), or nanoparticle mass, density, and dynamic shape factor (when combined with a mobility or mass analyzer).

A paper describing the theory behind the instrument has been published (Tavakoli and Olfert, 2013). A prototype of the instrument has been built and tested and experimental results from the instrument were published. A paper was also published using the AAC and DMA to determine mass and morphological properties of soot and other particles (Tavakoli and Olfert, 2014). US, Japanese, and Canadian patents have been granted the patent is pending in Europe. The AAC has been licensed by Cambustion Ltd.

Climate forcing potential of soot
Soot is generally considered to be the second largest contributor to global warming (after carbon dioxide and before methane) and impacts of climate change “include alteration of ecosystems, disruption of food production and water supply, damage to infrastructure and settlements, morbidity and mortality” (Intergovernmental Panel on Climate Change, 2014). However, there is uncertainty on how condensed material on the soot particles alters their optical properties (and climate-warming potential) when they are in the atmosphere. Understanding how soot particles restructure to more compact shapes when this material condenses on them is key to reducing this uncertainty so that appropriate climate policy and regulations can be developed.

Research on the optical properties of these particles was conducted in collaboration with a large international research team (Cappa et al. 2012; Cappa et al. 2013). The paper describes field measurements of optical properties of soot particles and contrasts these results to laboratory measurements. The results of these papers are very significant because they show that the climate-forcing potential of the atmospheric soot was much lower than what was expected from climate models and some laboratory studies. I was involved in the laboratory experiments in this study. I developed an instrument called the centrifugal particle mass analyzer (CPMA) that measured the mass of the condensed material on the soot. This instrument was an important component of these experiments as the CPMA was used to determine the mass of the condensed material and this mass is critical in the interpretation of the data.

With the CPMA, we have been able to expand this work in my lab with focused studies on the restructuring of soot particles. We showed that the degree of restructuring of the soot particle is dependent on the mass of condensed material on the soot (Ghazi and Olfert, 2013). More recently, we have been conducting soot restructuring experiments using a smog-chamber to generate soot coated with atmospherically-relevant condensed material (i.e. “secondary organic aerosol”, SOA). Through this study we have shown that several different precursors (toluene, p-xylene, ethylbenzene, and benzene) produce SOA which all restructure soot to the same degree (Schnitzler et al, 2014). The knowledge gained from these studies will help climate modelers develop models which can better predict the climate forcing potential of soot.

Centrifugal Particle Mass Analyzer (CPMA) for mass calibration
Much of my work has been focused on developing the CPMA and the instrument became commercially available from Cambustion Ltd in January 2012. The CPMA uses opposing electric and centrifugal fields to classify aerosol particles according to their mass-to-charge ratio. Recently, we developed a new method using a CPMA and an aerosol electrometer to provide a stream of particles of known mass concentration for real-time instrument calibration. This technique is an exciting development in aerosol instrumentation as it provides a traceable calibration method for mass instruments (Symonds et al. 2013). In this publication I provided a theoretical analysis for the effects of CPMA resolution on the uncertainty in the method and I also developed a method to estimate the bias due to uncharged particles in the system. We have recently demonstrated this technique, and explored sources of error, by calibrating soot mass concentration instruments (Dickau et al., 2015) that are typically used in automotive and aircraft emission research.

Using the CPMA to develop soot instruments
Due to the importance of soot from a climate perspective, many real-time instruments have been developed to measure soot in the atmosphere. The CPMA is a very useful tool for measuring the properties of soot and for calibrating instruments that measure soot. In particular, we used the CPMA in a large international collaboration to measure the microphysical properties of soot and used this information to calibrate and characterize real-time soot instruments for atmospheric measurements (Cross et al. 2010). This led to the characterization of the detection limit of an instrument called the single particle soot photometer (SP2) (Schwarz et al. 2010). Later work was done to measure the properties of black carbon reference materials for SP2 calibration (Gysel et al. 2011). These papers are widely used by researchers to understand the limitations and uncertainties in these instruments.

Fast Integrated Mobility Spectrometer
Another instrument I have developed is the fast integrated mobility spectrometer (FIMS). The FIMS measures the size distribution of particles by detecting the mobility of charged particles in an electrostatic field. I developed an inversion algorithm for the instrument so that the size distribution of the particles can be determined from the electrical mobility measurements of the instrument (Olfert et al. 2008). Furthermore, I have analyzed the dynamic characteristics of the FIMS to understand the errors associated with very fast measurements with the instrument (Olfert and Wang, 2009). The unique capability of the FIMS (high sensitivity and fast response time) makes it an ideal instrument for aircraft-based aerosol atmospheric studies. The FIMS was deployed in the Cumulus Humilis Aerosol Processing Study (Berg et al. 2009)

Miniature Inverted Soot Generator
I have worked on the development of the Miniature Inverted Soot Generator sold by Argonaut Scientific. The Miniature Inverted Soot Generator produces a steady stream of soot particles for use in aerosol research and aerosol instrument calibration.