Research
Poster presented at the International Aerosol Conference 2022
How do airports change air quality nearby?
{Presented at the International Aerosol Conference 2022}
Particles are a major component of air pollution, but not all particles are alike. Our body naturally filters large particles. Small particles, however, can easily circumvent the natural filters in our body and reach the deepest crevices of our lungs where they are absorbed. Ultrafine particles, or particles less than 100 nanometers in diameter, are one class of particles that can seriously degrade health, but their impact depends on their chemical composition. These particles are frequently detected around airports and evidence suggests these particles are made of aircraft oil and maybe jet fuel molecules. Here, we presented preliminary findings from laboratory studies of aircraft oil and jet fuel chemical composition. We artificially created particles out of new and used aircraft oil to measure their molecular fingerprints. We have since used this information to confirm the presence of aircraft oils on nanoparticles in engine exhaust. We are continuing this analysis with many more conference presentations and papers to come soon.
How can we simplify the chemical soup of smoke plumes?
{Published in Environmental Science and Technologoy}
This is a question many atmospheric scientists ask whether they study a smoke plume, a power plant plume, or an urban plume. Chemistry can differ between the plume center, which is typically darker and denser, and the edge, which is typically lighter and influenced by cleaner air around the plume. In the case of a smoke plume, these differences can be extreme! In some cases, the plume center can completely block out sunlight mimicking nighttime conditions and thus different chemical regimes. When we study plumes by aircraft we typically fly the aircraft through the plume perpendicular to the direction the plume is traveling (a.k.a. the prevailing wind direction). With each pass through the plume, we gather a slice of observations from the plume edge, to the center, and to the other edge. These simple crosswind transects can show complex chemical differences that are very difficult to interpret. To make the job easier, we developed a new method called The Gaussian Observational Model for Edge to Center Heterogeneity (GOMECH). This general method transforms complicated observations into smooth curves that we can more easily interpret. With this new method, we are able to quantifiably differentiate chemical oxidation processes at the plume center and edge, which change over time and from sunrise to sunset.
To learn more about GOMECH and what is taught us about oxidation chemistry in smoke plumes check out the paper now in Environmental Science and Technology.
Summary figure of a novel model technique termed GOMECH
The inside of the NOAA Chemistry Twin Otter viewed from the aft mid-flight.
What does the chemistry of a real smoke plume look like?
{Published in Atmospheric Chemistry and Physics and presented at the American Geophysical Union 2020 conference}
With some knowledge of what smoke plume chemistry to expect, we brought a scientific laboratory into the air to sample wildfire smoke directly. As part of the FIREX-AQ (Fire Influence on Regional to Global Environments Experiment - Air Quality) research campaign. FIREX-AQ was a major field research campaign with over 100 scientists from NOAA, NASA, and several universities. My focus during FIREX-AQ was on nighttime smoke plume chemistry. I want to understand what chemistry takes place at night, and how that can affect air quality in nearby populations. I was aboard the NOAA Chemistry Twin Otter operating the University of Washington (UW) Iodide Chemical Ionization Mass Spectrometer alongside scientists from the University of Washington. Several other instruments were aboard the NOAA Chemistry Twin Otter and together we measured hundreds of smokes molecules as wells as information on the size and properties of the smoke’s particulate matter.
Check out the paper with the button below or watch a synopsis I presented at the American Geophysical Union 2020 conference.
How do smoke molecules change at night compared to the day?
Sunlight plays a role in smoke chemistry. Just as sunlight provides energy for plants to grow, sunlight gives energy to molecules. Sunlight can speed up a reaction, or it can tear apart a molecule. Some of the most important atmospheric chemistry happens because of sunlight, and other important reaction don’t happen because of sunlight. Researchers from NOAA (that’s me!), Colorado State University, University of Wyoming, University of California Berkeley, and University of Washington gathered at the NCAR Environmental Chamber for this study called MOONLIGHT (Monoterpene and Oxygenated aromatics Oxidation at Night and under LIGHT). We mixed the most important smoke molecules, one at a time, with other gases in a large Teflon (special plastic) bag. We used UV lights to simulate sunlight, or we let reactions happen in the dark to simulate night. We then sampled some of the gases from the bag with different instruments to monitor what molecular products form, and how much particulate matter is made.
The NCAR Environmental Chamber during MOONLIGHT
How do the most important smoke molecules react at night?
{Presented at the American Geophysical Union 2019 conference}
We have some understanding of which smoke molecules are most reactive as well as what chemical products they create after a night of smoke aging. What we don’t understand well is how to get from reactant to product. What we want is a chemical mechanism to explain how molecule A reacts with molecule B to make molecule C. In reality, these mechanisms involve multiple intermediate molecules (molecules D through Z maybe). These intermediates are very important because it gives us an idea of how long it takes to make the final product and what other important molecules might be formed. To study these mechanisms we designed and built a temperature-controlled Dark Oxidation Flow Reactor (DOFR) to react a nighttime oxidizer (NO3 from N2O5) with various smoke molecules (mainly oxygenated aromatics). We can control how long the molecular reaction is allowed to proceed and we sample all of the gas-phase products at the outlet of our DOFR with a quadrupole chemical ionization mass spectrometer (qCIMS). The results we have seen so far are exciting and may have implications for both smoke plume models and in situ smoke measurements.
What smoke molecules are most important at night?
{Published in Environmental Science and Technology and presented at the American Geophysical Union 2018 conference}
The smoke from fires (biomass burning) contains thousands of different molecules. When the summer smoke haze reaches our town or the winter smell of a fire place reaches our nose we are breathing in these molecules. To understand how those molecules affect our health we must first know which molecules are actually in smoke! To make things more difficult, a lot of the molecules evolve - they react and change - as the smoke ages. Going further, nighttime smoke and daytime smoke change differently because of sun exposure. In this research article my coauthors and I detail which smoke molecules are likely the most important, and how they change overnight. We consider smoke from a typical western wildfire and smoke from a crop burning. It turns out that smoke undergoes some important changes at night that likely leads to degrading air quality the following day.
How fast do molecules react in the atmosphere?
{Published in Physical Chemistry Chemical Physics}
The atmosphere has a lot of different molecules and all of these interact with each other in some way. To know which interactions are important, we have to know how quickly they interact. If it’s slow, then maybe the interaction isn’t so important. But, if it’s fast, it could be. My coauthors and I considered two molecules: isoprene and formaldehydeoxide (Criegee intermediate). Isoprene is important because it is the most emitted molecule in the world. It comes from plants! Formaldehydeoxide is much more elusive because it only exists for mere milliseconds. We reacted these two molecules together and watched how long it took for all of the formaldehydeoxide to react away. We tested the reaction with many temperatures and found that they reacted more quickly at higher temperatures. We also figured out how these molecules interact on the nano-scale by running computer simulations. It turns out that they can interact in about 16 different ways, but all of these interactions are somewhat slow.