Last Updated: August 26, 2021
Our research focuses on better understanding the chemical composition of the atmosphere, its perturbation by human activity, and the implications for life on Earth. We use advanced models of atmospheric composition to interpret observations from satellites, aircraft, ground networks, and other platforms. We view our models as part of an integrated observing system to increase fundamental knowledge and address pressing environmental issues.
We have a large number of ongoing projects at any given time, addressing broad research themes and organized in subgroups as described further below. In addition to these research-focused subgroups, we have three other organized subgroups:
- Machine Learning & Data Science (MLDS) subgroup - for discussing MLDS applications to atmospheric chemistry research. Leaders: Daniel Varon, Makoto Kelp, and Drew Pendergrass
- Diversity, Inclusion, and Belonging (DIB) subgroup - for continually improving our practices. Leaders: Eimy Bonilla and Hannah Nesser
- GEOS-Chem Support Team - responsible for development and support of the GEOS-Chem model.
Air quality in China is among the worst in the world and the Chinese government has declared a "war on air pollution" involving massive controls on emissions. Newly installed surface air quality networks together with satellite observations allow us to track the evolution of Chinese air quality and the responses to emission controls, to better understand the factors controlling particulate matter and ozone pollution, and to make recommendations for future emission control strategies.
Air quality standards in developed regions of the world are becoming tighter and tighter, yet the observations often show no improvement despite increasing emission controls. This may be because of background sources of air pollution, including natural sources and pollution transported on intercontinental scales. This pollution background is poorly understood but it may prevent air quality standards from being achievable. It also complicates the interpretation of satellite observations for air quality.
Tropospheric oxidants (ozone and OH) are of central importance for global atmospheric chemistry. The hydroxyl radical (OH) is the main atmospheric oxidant responsible for removal of atmospheric gases yet we have little understanding of the factors controlling it and the associated long-term trends. Ozone is a major greenhouse gas in the middle/upper troposphere, a toxic gas at the surface, and the primary source of OH, but the factors controlling its global distribution and long-term trends are poorly understood. Chemical production and loss of ozone and OH involve complex nonlinear mechanisms coupled to transport on all scales. Key questions relate to the sources and chemistry of nitrogen oxides (NOx), oxygenated volalile organic compounds (VOCs), and halogens.
The atmospheric chemistry of volatile organic compounds (VOCs) has major implications for oxidant concentrations and for formation of organic aerosol. VOCs are emitted from a range of biogenic and anthropogenic sources. They undergo various oxidation cascades in the atmosphere, producing increasingly substituted and cleaved compounds, terminating eventually in the formation of CO2, the formation of secondary organic aerosol (SOA) or the removal by deposition. Most of the species and reactions involved have never been measured and must be inferred indirectly. Multigenerational products of VOC oxidation may be responsible for an "organic soup" in the remote troposphere that is suggested by observations but not understood at all. Representing organic chemistry in models is a major challenge.
Mercury deposition to ecosystems results in accumulation of toxic forms of mercury up the food chain. Mercury is emitted to the atmosphere mostly as Hg(0), and is oxidized in the atmosphere to Hg(II) which can be rapidly deposited but also reduced back to Hg(0). Understanding atmospheric Hg(0)/Hg(II) redox chemistry is crucial to predicting the patterns of mercury deposition and the subsequent biogeochemical cycling.
Anthropogenic emissions of methane come from a very large number of relatively small point sources including coal mine vents, oil/gas production and processing facilities, stockyards, landfills, etc. These sources have highly variable emissions, and can spike under abnormal conditions. Satellites provide a unique vantage point for global continuous monitoring of point sources. Several new instruments with high pixel resolution hold particular promise.
Methane is the second most important anthropogenic greenhouse gas after CO2. It is particularly important for near-term (~20 years) climate change. Methane is emitted by a wide range of processes including oil/gas systems, livestock, landfills, wastewater, rice cultivation, and wetlands. The magnitudes of these sources, their spatial distributions, and their temporal trends are poorly understood. Improving the "bottom-up" inventories that relate emissions to activity levels is imperative for climate policy. This can be done by using state-of-science activity and emission factor data, evaluating the resulting inventories with atmospheric observations through "top-down"inverse analyses, and using the results of these inverse analyses to further improve the emission inventories. This partnership between bottom-up and top-down approaches is key to improving understanding of methane emissions in a way that can enable policy action.
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