TEAMPACCC
Trends in Earth's Atmospheric Makeup: Pollution of the Air - Chemistry - Climate Connections
Trends & Variability In
Atmospheric Constituents
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.
Tropospheric Ozone Trends
Upper tropospheric ozone has increased rapidly in recent decades, in contrast to changes in lower tropospheric ozone which is more directly influenced by near-surface anthropogenic precursor emissions. This decoupling of ozone trends in the upper and lower troposphere suggests a growing prominence for tropospheric ozone as a greenhouse gas despite regional efforts to abate warm season ground-level ozone (Fiore et al., 2022). The extent to which upper tropospheric ozone trends are due to natural climate “noise” or externally forced “signal” is unknown. By applying a pattern-based fingerprint method developed for climate applications we show that the anthropogenic fingerprint of increasing upper tropospheric ozone trends is identifiable with high statistical confidence in an available 17-year satellite dataset (Yu et al., 2024). Our analysis also reveals regions and seasons with strong anthropogenic change signals relative to internal variability, which can guide future observing systems targeting rapid detection of anthropogenic impacts on tropospheric ozone. We are actively investigating the role of specific ozone precursors in driving these trends. [Xinyuan]
Aviation NOx is a rapidly growing anthropogenic source of tropospheric ozone. The best estimate of global aviation NOx emissions prior to the pandemic (2016) is approximately 1.2 Tg-N yr-1 (Oh et al., 2026), with projections indicating a potential increase by 2050 due to growing air travel demand and limited alternatives to combustion based propulsion. Because NOx emitted at cruise altitude is highly efficient at producing ozone, present day aviation emissions disproportionately influence the tropospheric ozone budget. Using a “plug-and-play” modularity developed in the CESM framework, including an option to use GEOS-Chem chemistry (“CESM-GC configuration”), we are identifying key sources of uncertainty in model estimates of aviation-induced tropospheric ozone. [Lucas]
Spatiotemporal variability in OH
There are large uncertainties in OH trends over 2005–2014, with disagreements between and within bottom-up (i.e. forward modeling) and top-down (i.e. inverse modeling) approaches. Trends in OH can be influenced by changes in emissions related to OH chemistry and climate conditions, as well as internally arising climate variability. Using a 13-member ensemble of CESM2 simulations, we find that 10-year trends in global OH are sensitive to internal climate variability. Then, we emulate airmass-weighted mean tropospheric OH using a fully connected neural network and satellite observations to interpret the role of chemical proxies. See Zhu et al. (2024) for details.
​
With NASA ATom measurements, we developed a ‘steady-state’ OH proxy that can be deconstructed to identify the underlying processes controlling spatial variations in OH and evaluate those relationships in chemistry-climate models (Baublitz et al., 2023). Murray et al. (2021) explored decadal trends and variations in OH by 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 to show that the fate of both reactive nitrogen and reactive carbon as represented in these models are key factors contributing to the inter-model differences.
Global annual-mean ozone burden in the CESM2-WACCM6 historical simulations. Thin lines show the 16 individual CESM2-WACCM6 ensemble members and thick lines show the ensemble-mean value in each year (Yu et al., 2024).