Tropospheric ozone is at the nexus of atmospheric chemistry and climate through its role as an air pollutant, greenhouse gas, and a regulator of the global oxidative capacity. Advancements in satellites measurements, global chemistry and transport models, and assimilation techniques provide powerful new tools and datasets to understand and quantify the processes controlling tropospheric ozone. Using these tools, I will discuss recent research based on ozone and CO profile observations from the NASA Aura Tropospheric Emission Spectrometer (TES) to quantify trans-Pacific transport of pollution, impact of surface emissions on tropical tropospheric ozone, radiative forcing from tropospheric ozone, and observational constraints on chemistry-climate projections. These results provide a backdrop to understand the measurement requirements for the next generation of atmospheric composition instruments such as GEO-CAPE. We will discuss the role of observing system simulation experiments (OSSE) as a tool to explore and define those requirements.