Atmospheric Chemistry, Air Pollution, and Climate
Air pollution poses a growing problem in both developed and developing urban centers. Anthropogenic emissions and their products have strong impacts on human health, leading to an estimated 4 million premature deaths in 2015 alone, predicted to grow to 6.5 million annually by 2040. The Okumura group investigates the chemical kinetics and mechanisms of pollutant-forming oxidation of volatile organic compounds and related atmospheric reactions via spectroscopic, mass spectrometric, and quantum chemical methods.
Anthropogenic emissions impact climate both directly via radiative forcing and indirectly through subsequent oxidation and aerosol-forming aggregation processes. The Okumura group performs laboratory studies in support of remote and direct sensing projects providing spatially and temporally resolved information on sources and sinks of atmospherically relevant species. In addition, we study the formation of secondary organic aerosols, which have complex impacts on climate via scattering, absorption, and modulation of cloud nucleation rates and lifetimes.
Developing Spectroscopic Techniques
study of chemical systems of ever-increasing complexity has placed
tremendous demands on spectroscopic sensitivity and resolution. In order
to study these systems, the Okumura group has been developing and
extending techniques in cavity ringdown spectroscopy, photoacoustic
spectroscopy, and frequency combs. In collaboration with the NASA Jet Propulsion Laboratory, the group has also developed compact, chip-scale spectrometers. Future interests include the application of spectroscopic techniques for the search for life in our solar system.
Planetary and Astrochemistry
The evolution of the chemical composition of planetary atmospheres is an active area of research. There is abundant evidence that Mars used to have flowing water; however, present-day Mars has no liquid water. One key to understanding the mechanism of water loss is the atmospheric D/H ratio, which is 6x enriched in deuterium relative to Earth's standard mean ocean water. This enrichment is consistent with preferential escape of lighter H atoms over D atoms from the top of the Martian atmosphere.
The process of Martian water loss is outlined above. Water is photolyzed, chemically transformed to long-lived H2, then transported to the top of the atmosphere, after which it can escape. While the chemistry underpinning the transformation of water to H2 is thought to be well understood, the effect of isotopic substitution on reaction rates is poorly characterized, or in many cases, entirely unstudied!
In the Okumura group, we are working on characterizing the kinetic isotope effect (KIE) of various HOx reactions in the Martian atmosphere, using both quantum chemical/in silico methods and direct experimental measurement.
Future interests include study of reactions relevant to other planetary atmospheres and the application of spectroscopic techniques for the search for life in our solar system.
- Kinetic Isotope Effect
- HOx chemistry of the Martian atmosphere