Trends and Variability in Atmospheric Constituents

We are studying the processes that influence daily-to-decadal variability and long-term trends in key atmospheric species.  Our work to date has largely focused on ozone and methane (see publications).  Current projects seek to identify proxies for variability in atmospheric oxidizing capacity (OH) on several scales (hourly-to-daily at local scales and inter-annual-to-decadal at the global scale), and the underlying factors governing the observed variability.

Formaldehyde variability as a proxy for methane oxidation

Using a suite of models ranging from short regional-scale simulations to centuries-long simulations with chemistry-climate models, we are probing the potential for formaldehyde to serve as a proxy for methane oxidation in the remote troposphere, and for the next generation of satellite instruments to provide observational constraints.  [Luke Valin, supported by a NOAA postdoctoral fellowship]

Further, we aim to constrain this proxy in the remote atmosphere, where we expect it to be most effective. We are pursuing this as a member of the ATom team of modelers, led by Michael Prather (UC Irvine). The relationship between formaldehyde and the methane loss rate is considered in clean air and in biomass burning plumes. [Colleen Baublitz]

Processes contributing to inter-model OH differences

Current models disagree on the magnitude of OH levels, as well as on the sign of the change in response to imposed anthropogenic emission changes, implying large uncertainties in the OH response to changing climate and natural emissions. We are examining 1860-2100 simulations available from the Atmospheric Chemistry Climate Model Intercomparison Project (ACCMIP) and two fully coupled transient chemistry-climate models (GFDL CM3 and GISS Model-E2), as well as the GEOS-Chem chemistry-transport model (click here to see Lee Murray’s interactive page displaying their time-varying OH estimates) to determine the key factors contributing to the differences across models.  [Lee Murray]

Funding: NASA, NOAA