48. A Retrospective Analysis of Ozone Formation in the Lower Fraser Valley, Canada

We conducted a study of ozone formation in the Lower Fraser Valley (LFV), using WRF-SMOKE-CMAQ models, observations and emission inventories in order to understand relationships between the reduction in both amount and location of precursor emissions and spatio-temporal changes in episodic ambient ozone concentrations over the last 20 years. A dynamical model evaluation shows that the modeling framework is able to capture the changes in both magnitude and spatio-temporal structure of ozone concentrations over the 20-year period. We model ozone formation for four episodes, which both capture the observed changes in ozone reduction and the different meteorological regimes that occur during LFV ozone episodes. The SMOKE emission inventories are adjusted to account for temporal changes in amount, and location of emissions, based on population shifts. Model runs allow us to isolate the effects of emission changes from meteorological changes. Results show that the western LFV has been, and remains VOC-sensitive; the central LFV has changed from VOC-limited to NOx-limited; and the eastern LFV has been, and remains NOx-limited. Analysis shows that the ozone production efficiency as a function of NO has increased noticeably in the eastern LFV. This has likely offset some of the benefits resulting from local NOx emission reductions.