Trends in Earth's Atmospheric Makeup: Pollution of the Air - Chemistry - Climate Connections
Trends & Variability In
We are studying the processes that influence daily-to-decadal variability and long-term trends in key atmospheric species, with a major focus on ozone, methane, and the hydroxyl radical.
Spatiotemporal variability in OH
Formaldehyde as a proxy for methane lifetime
Using measurements obtained during the Atmospheric Tomography (ATom) field campaign and
chemistry-climate model simulations, 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 new regional-scale observational constraints on OH. [NASA, Colleen Baublitz; NOAA postdoctoral fellowship to Luke Valin]
A ‘steady-state’ proxy for OH
We are also using ATom measurements and chemistry-climate models to develop a ‘steady-
state’ OH proxy that can be deconstructed to identify the underlying processes controlling OH
variability. [NASA, Colleen Baublitz, Lee Murray]
Processes contributing to inter-model OH differences
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 examined 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 to show that the fate of both reactive nitrogen and reactive carbon as represented in these models are key factors contributing to the differences across models. See Murray et al. (2021) for details. [NASA postdoctoral fellowship to Lee Murray]
Influence of climate variability on tropospheric composition
Deep stratospheric ozone intrusions over the Western U.S.A.
With a high-resolution (~50 km x 50 km) configuration of the GFDL AM3 model, we found that deep stratospheric ozone intrusions over the high-altitude western U.S.A., and found that these events can push ozone levels above the National Ambient Air Quality Standard for ozone (Lin et
al., 2012). Multi-decadal simulations with the GFDL AM3 chemistry-climate model further revealed a connection between southward meanders of the polar jet during late spring and early summer, such as occur following wintertime La Niña events, and the frequency of deep intrusions that affect the high tail of the ozone distribution over the western U.S.A. (Lin et al., 2015). Seasonal predictability (a few months lead time following La Niña events) could allow western U.S. air managers to prepare for a high-ozone season by deploying observational platforms to identify these events and issue timely public health warnings. [NASA AQAST, NOAA]
Tropospheric ozone trends
With historical CESM2-WACCM6 chemistry-climate initial condition ensemble simulations, we
are working to identify ‘forced’ trends (e.g., by anthropogenic emissions or climate change) in tropospheric ozone. Please see Deser et al. (2020) for some examples of how full chemistry initial condition ensemble simulations, including from multiple models, could be applied for tropospheric chemistry, air quality and public health applications.