Sensitivity of Surface-Level Ozone to Temperature-Related Processes

The response of surface-level ozone (O₃) to changing temperatures can be easily elicited from observational data, but the underlying causes of the observed strong, positive relationship cannot be inferred from observations. For example, the emissions of anthropogenic O₃ precursors and the chemistry of O₃ production are both highly temperature-dependent, while the transport of O₃ and precursor gases varies with temperature, but the relative role of these processes in causing the O₃-temperature dependence is not known. In our present work we use the Global Modeling Initiative (GMI) chemical transport model (CTM) to isolate the drivers of daily O₃ variability in the Northeastern U.S.

A suite of sensitivity simulations is performed with differences in the daily variability of different temperature-related processes. This includes simulations with and without daily variability from NO_x emissions from power plants and industrial facilities and simulations with and without daily temperature variability of chemistry-related fields. Preliminary analysis indicates that variability in anthropogenic emissions play a very small role in the daily variability of ozone in the focus region. Temperature-related variations in chemistry play a larger role, but this is not the dominant cause of the O₃ variability. Rather, these results point to the importance that transport plays on O₃. In showing this we integrate in-situ observations from air quality monitoring networks such as CASTNet and AQS and the MERRA-2 reanalysis to discuss meteorological regimes which contribute to the strong influence of transport on O₃, especially as it pertains to extreme events.